A SELF-GUIDED TOUR OF ROUND TOP VOLCANOES by gap18103

VIEWS: 9 PAGES: 1

									A SELF-GUIDED TOUR                                                                                  FIS
                                                                                                          H RA
                                                                                                               NCH
                                                                                                                                           Hwy. 24 on-ramps
                                                                                                                                           TO WALNUT CREEK
                                                                                                                                                                                                                                                                                                                                                                  reddened by baking; these bands are called “bake zones.”
OF ROUND TOP VOLCANOES
                                                                                                                     RO
                                                                                                                       AD                  AND OAKLAND                        IN ORDER TO REDUCE OR PREVENT THE RISK                                                                    MEMBERSHIPS                                                               A related process occurs when a brushfire reddens rocks
                                                                                                                                                                              OF SERIOUS HEAD INJURY OR DEATH, STATE                                                        The Regional Parks Foundation
                                                                                                         Fish Ranch R                                                         LAW REQUIRESTHAT ALL BICYCLISTS UNDER                                                         offers memberships to park users.                                                     and soil. To see Post 6, walk down the road about 100 feet
                                                                                                 1.08 to                                                                      AGE 18 WEAR AN APPROVED HELMET WHILE                                                          Benefits include free parking,                                                        past Post 5, then bear to the right.




                                                                                                                          oa
By Stephen W. Edwards                                                                                                                                                         RIDING ON TRAILS AND ROADWAYS. THE                                                            swimming, and off-season camping




                                                                                                                            d
                                                                                                       TT
                                                                                                                                                                                                                                                                                                                                                                       Before you is a wall with basalt on the left and Orinda
Director, Regional Parks Botanic Garden                                                                                                                                       DISTRICT ALSO STRONGLY RECOMMENDS                                                             discounts, depending on member-
                                                                                                                                                                                                                                                                                                                                                                  6




                                                                                                      O
                                                                                                                                                                              THAT ALL EQUESTRIANS AND ALL BICYCLISTS                                                       ship category. For more information,




                                                                                                                         SK
                                                                      T                                                                                                                                                                                                                                                                                                mudstones on the right. The bedding in the mudstones is




                                                                                                  EC
                                                                    an o F




                                                                                                                EL
                                                                                                                                                                              WEAR HELMETS AT ALL TIMES.                                                                     call (510) 544-2203.




                                                                                                                          YL
                                                                                               LD
Robert Sibley Volcanic Regional Preserve features a complex           d ish




                                                                                                                              INE
                                                                                                                                                                                                                                                                                                                                                                  disrupted, giving the appearance of drag-folding resulting




                                                                                                               N
                                                                        H R




                                                                                                            N
                                                                                                                                              LAND BANK AREA




                                                                                             A
                                                                          w a




                                                                                                                                                                                                                                       1500
volcanic center that was the source, 10 million years ago, of




                                                                                                          TU
                                                                           y. n                                                               CLOSED TO PUBLIC                                                                                                                                                                                                    from relative uplift of the lava occurring during the past 10




                                                                                           C




                                                                                                                                NA TI
                                                                     BA      24 ch                                                            (EXCEPT ALONG SKYLINE TRAIL)                                                                     9
most of the lavas that underlie the ridges from Inspiration             YF         Ro                                                                                                            CLOSED TO PUBLIC                                         8
                                                                                                                                                                                                                                                                   Quarry Pit
                                                                                                                                                                                                                                                                                                                                                                  million years. Alternatively, the disruption of the mudstones
                                                                                      ad                                                                                                                                                                               7




                                                                                                                                      O
                                                                      D




                                                                      ORE
Point in Tilden Regional Park to Moraga. Round Top, one of                                                                                                                                                                                                                                                                                                 1100   may have occurred earlier, at the time of volcanic activity.




                                                                                                                                    NA
                                                                                                                                                                                                                                  .12




                                                                        RIV
                                                                                                 GR




                                                                                                                                                                                                CLOSED TO PUBLIC
                                                                          ST




                                                                                                                                               10
                                                                                                                                       L
the highest peaks in the Berkeley Hills, consists of lavas,




                                                                                                                                                                                                                                              VO
                                                                           E
                                                                                                                                                                                                                           .15                 LC                                                                                                  1200           This site was close to, or was in, the wall of the caldera, and




                                                                                                                                                        11
                                                                                                                                                  00
                                                                                                                                                                                                                                                                                      View of Mt. Diablo




                                                                                                    IZ
                                                                                                                                                                                                                                                    AN




                                                                                                                                                         00
breccias (unsorted mixtures of fine and coarse volcanic deris)




                                                                                                      ZLY




                                                                                                                                                                                                                                                                       .11
                                                                          TUNNEL                                                                                                                                                                                                                                                                                  would have been subject to all kinds of slumping, sliding and
                                                                    O LD                                                                                                                                                                                                                                                                         1300




                                                                                                                                                                                                                                                          IC
                                                                                                                                                                                                                                                                 .28
and tuffs (lithified volcanic ash—ash that has become stone)           R OAD                                                                                                                                                                                                                                                      1400                            plowing. The “exotic” large sandstone blocks lying about
that once filled a volcano.




                                                                                                                                                                                                                                                    .2
                                                                                                                                                                                                                                                                                       .04             .27                                                        were torn from very ancient Cretaceous (Age of Dinosaurs)




                                                                                                                                                                                                                                                         9
                                                                                                                                                     RE




                                                                                                          PE
                                                                                 SK
                                                                                                                                                       CR                                                                                                                                                                    1500
     Though Round Top was once the infilling of a great caul-                                                                                                                                                                                                                                  .07




                                                                                                            AK
                                                                                                                                                                                                                                                                                                                                                                  rocks by the ascending lavas. The quarrymen took the lava,




                                                                                    YL
                                                                                                                                                         EA                                                                                                                          .03
                                                                                                                                                           TI                                                                                                                                               6




                                                                                        IN
                                                                                                                                              11 0
dron, it stands out today because it was originally surrounded                                                                                     0         ON                                                                                                                                                                                                   but left the sandstone here. To see Post 7, proceed northwest




                                                                                                                                                                                                                                                                                             TR
                                                                                           E
                                                                                                                                 1200




                                                                                                                                                                                                                                                                                              AI
                                                                                                                                                                                                                                                          1300
by “incompetent” (easily eroded) sedimentary rocks of the                                                                       1300                          TRAIL                                                                                                                                                 5                                             along the main road, then take the first right.




                                                                                                                                                                                                                                                                                                   L
Orinda Formation, which have eroded away. During the past                                                                                                                                                                                                                                                                          1600




                                                                                                                                                                                                                                                                                                       .1
                                                                               BL
                                                                                                                                          LAND BANK AREA                                                                                                                                                                                                               Massive basalt was removed from this major quarry




                                                                                                            BLV
                                                                                                                                                                                                                                                                                                                                                                  7




                                                                                                                                                                                                                                                                                                        3
                                                                                 VD
                                                                                                                            0
                                                                                                                         140              CLOSED TO PUBLIC                                                           .87




                                                                                                                                                                                            LAND BANK
                                                                                    .
10 million years the Berkeley Hills were uplifted on a gigantic                                                                                                                                                                                                                                                                                                        pit. The north wall shows a set of thick lava flows. They




                                                                                                               D.
                                                                                                                                          (EXCEPT ALONG SKYLINE TRAIL)                                                             0
                                                                                                                                                                                                                             11 0                                                                                                         Quarry Pit
scale because of strains on the Hayward and Moraga fault                                                                                                                                                                                                                             140
                                                                                                                                                                                                                                                                                        0                                                                         are tilted on edge, nearly vertical, with a bake zone at the




                                                                                                                                                                                                                                                                                                                            .11
systems. This uplift folded the rock formations, and the Round                                                                                                                                                                                                                                                                                                    base of the sequence (far left). The well-defined layers near




                                                                                                                                                                                                                                                                                                                                            .04
                                                                                                                                                                                                                                                                                               TOP                      3
Top vent complex was tilted on its side. Hence, folding and                      LEGEND                                                                                                                                                                                    .4
                                                                                                                                                                                                                                                                                1      ND      15
                                                                                                                                                                                                                                                                                                  00            2                    4
                                                                                                                                                                                                                                                                                                                                                                  the top of the face are jointing-units resulting from cooling.
                                                                                                                                                       GRIZ Z LY                                                                                                                    OU




                                                                                                                                                                                                                                                                                                                              LOOP
erosion have exposed a cross section of a great volcano, right                 Hikers, Horses & Bicycles                                                                        PE                                                                                                                                                                                Another interesting outcrop is situated on the remnant of an




                                                                                                                                                                                                                                                                           R
                                                                                                                                                                                     AK                                                                                                              00
down to its roots, providing an unsurpassed outdoor laboratory                 Hikers and Horses                                                                                                                                     00                                                            16                                                             old road along the southeast flank of this peak. There you can
                                                                                                                                                                              .63                                                 12                                            1                                                    .17
for the study of volcanism in the Central Coast ranges.                        Skyline National Trail/                                                                                                                                                                                             Round Top                                                      see a thick accumulation of cemented red-baked volcanic




                                                                                                                                                                                                                                                                                                                                         TRAIL
     The blocks of stone scattered everywhere around the                       Bay Area Ridge Trail                                                                                                                                                                                                1763                                                           cinders. These kinds of deposits always indicate proximity




                                                                                                                                                                                                                                    0
                                                                                                                                                                                                                                                                                                                                                    1500




                                                                                                                                                                                                                                    0
                                                                                                                                                                                                                                 13
                                                                               (Hikers and Horses)




                                                                                                                                                                                                                                                                                                                             17
flanks of Round Top are basalt lava (a hard, dense, dark                                                                                                                                                                                                                    Water Tank                                                                            of a vent. Loose deposits of comparable material are quarried




                                                                                                                                                                                                                                                                                                                              00
                                                                                                                                                                                                                           BAY
                                                                                                                                                                                                                                                                            .02
volcanic rock). Lava within the vent has been dated at UC                      Mileage Between Points




                                                                                                                                                                                                                   BLV
                                                                                                                                                                                                                                                                                                                                                                  at volcanic vents in Lake County, and the products end up as




                                                                                                                                                                                                                                                                                                                                     1600




                                                                                                                                                                                                                                                                                                                                                          1400
Berkeley, by the potassium-argon radioisotope dating method,                                                                                                                        KY                                                         .24




                                                                                                                                                                                S
                                                                               Stream or Creek                                                                                                                                                                                                                                                                    red-cinder mulch on gardens in the Bay Area.




                                                                                                                                                                                                                    D.
                                                                                                                                                                                                                                                                           .15                                               .35




                                                                                                                                                                                                                                                                                      .18
                                                                                                                                                                                         LI




                                                                                                                                                                                                                                 AR
at 9.5 million years before present.                                                                                                                                                        N                                                      .22
                                                                               Parking                                                                                                                                                                                                                                                                                 This is a red-baked sequence of air-fall tuffs. At the base
                                                                                                                                                                                                                                                                                                                                                                  8




                                                                                                                                                                                                                                   EA
                                                                                                                     N                                                                                                                                                                             .08




                                                                                                                                                                                            E
                                                                                                                                                                                                                                                         .15
     A great diversity of volcanic phenomena is preserved for                  Restroom                                                                                                                                                                                                                                                                                is a lava flow. Within the section are buff-colored thin




                                                                                                                                                                                                                                                                                                                                            .36
                                                                                                                                                                                                                                                                                             .03
                                                                                                                                                                                                                                                                                                                 .03




                                                                                                                                                                        DR.
study at Sibley. Basaltic dikes (feeders of the vents), tuff-              W   Water                                                                                                                                                                             2.94 miles from                         .08                                                      bands that look like lava. They are really air-fall tuffs that
                                                                                                                                                                                                                            B LV D .                             Round Top Loop
breccias (ash containing a scattered jumble of blocks and                      Visitor Center                                                                                                                                                        W           Trail southeast to                R                                                              were, for some reason, more strongly lithified than the other
chunks of lava), lava flows, red-baked cinder piles, air-fall                                                                                                                       EL                                                                           Skyline Gate in




                                                                                                                                                                                                                                                                                                   ID
                                                                                                                                                                                      VE                                                                         Redwood                                                                                          tuffs in the section. Volcanic ash, which is called tuff when




                                                                                                                                                                                                                                                                                               GE
                                                                               Gate




                                                                                                                                                                  ALE
                                                                                                                                                                                            RT
tuffs and the major vent itself can all be seen first-hand in the                                                                                                                                           ON                                                   Regional Park                              13
                                                                                                                                                                                                                                                                                                                 00                                               lithified, generally consists of rock fragments, crystals and
                                                                               Pond




                                                                                                                                                                  ND
course of an easy hike. Numbered posts, which correspond                                                                                                                                                                                                                                                              HUCKLEBERRY                                 bits of glass ejected from a volcano. Most of the tuffs at Sibley
                                                                                                                                                                                                                                                                                                                      BOTANIC




                                                                                                                                                              OR
to the numbered descriptions below, have been placed at some                            Scale




                                                                                                                                                                                                                                                                                                            00
                                                                       0                                       1/4 Mile                                                 OAKLAND                                                                                                                                       REGIONAL                                    have very little glass and would thus be called “lithic-crystal”




                                                                                                                                                                                                                                                                                                          12
                                                                                                                                                                                                                                 DR




                                                                                                                                                             TH
of the most interesting outcrops.                                                                                                                                                                                                      .                                                                              PRESERVE
                                                                              Contour interval 20 feet
                                                                                                                                                                                                                                                                                                                                                                  tuffs. The thin, hard, buff-colored bands in this section are
                                                                                                                                                                                                                                                                                                                        TR
     To visit this site, walk up the paved road to the EBMUD
1                                                                        Mileages courtesy Hal MacDonald,                                                                                                                                                                                  110
                                                                                                                                                                                                                                                                                              0
                                                                                                                                                                                                                                                                                                                                                                  “vitric-lithic-crystal” because they contain glass shards.




                                                                                                                                                                                                                                                                                                                         AI
                                                                                 EBRPD volunteer
     water tank. A dark basalt dike, an important feeder of                                                                                                                                                                                                                                                                                                            This is a beautiful basalt lava flow. It is smooth and




                                                                                                                                                                                                                                                                                                                           L
lava to the caldera, cuts through a sequence of tuff-breccias                                                                                                                                                                                                                                                                                                     9    massive in its upper part, to the left. The lower part is
(brown) and pebbly mudstones (gray), all inside and near the                These tuff-breccias originated when fluid mixtures of ash,                                                                              Miocene hill or peak. This unit also curves eastward through the                                                                              vesicular and “jumbled.” The lower parts of lava flows are
bottom of the caldera. The mudstones indicate ponding of               3    lapilli (small pieces of lava, and pebbles derived from the                                                                             bay-laurel grove in the gully to the right. The steep wall across                                                                             often jumbled by turbulence and drag. The vesicles in this
water; the tuff-breccias are the remains of landslides and             Orinda gravels) and blocks of lava, perhaps saturated by rain,                                                                               the pit consists of lava that formed the basalt dome. Eventually                                                                              flow were caused by escaping gas. The zeolites, chalcedony,
blockfalls into the pit from the surrounding walls.                    slurried and rumbled down the inside slopes of the volcano. In                                                                               the Round Top vent completely buried itself in basalt flows.                                                                                  opal and calcite filling many of the vesicles were precipitated
     Note Orinda Formation river sands and gravels on the
2    left against basalt lava on the right. This is part of the
                                                                       this outcrop there are two grades of breccia, the one at the bottom
                                                                       and the one to the right, bearing a much higher proportion of
                                                                                                                                                                                                                    From this point, note the view of Mt. Diablo, which, though it
                                                                                                                                                                                                                    contains some submarine volcanic rocks, is not, and never was,
                                                                                                                                                                                                                                                                                                                                                                  during and after cooling of the lava. Alternatively, the outcrop
                                                                                                                                                                                                                                                                                                                                                                  can be interpreted as two separate lava flows.
wall of the caldera. As you walked along the road to this              broken-up chunks of lava.                                                                                                                    a volcano.                                                                                                                                    HOW MANY VOLCANOES? Round Top was the big one.
point, you passed the steep cliffs below the summit installation.           This quarry pit was made by quarry operations in which huge                                                                                  This roadcut exposes Orinda Formation river gravels,                                                                                     There are smaller ones outside the Preserve on private property
These cliffs expose mostly colluvium (recently accumulated             4    amounts of massive basalt lava were removed. The result is                                                                              5    sands and mudstones. A cross-cutting basalt dike at the left                                                                             to the north and southeast. Another, of rhyolitic composition
slope debris), but there are also numerous outcrops of                 a tremendous boon to geology, for the pit exposes the interior of                                                                            end feeds into the overlying volcanics. The red streaks and layers                                                                            like the ash from Mount St. Helens, underlies the Lawrence
cataclastic basalt flows that look much like the colluvium.            the Round Top volcano. You are standing on bedded tuff-breccias,                                                                             in these river beds were caused by oxidation of iron in the                                                                                   Berkeley Laboratory and Little Grizzly Peak in Tilden Regional
Cataclastic means the flows were shattered into coarse blocks          which filled much of the caldera, settling at times into a small                                                                             sediments. Such varicolored “redbeds” are explored worldwide                                                                                  Park. About 9 million years ago it was erupting beside Round
by violent motions within the caldera — perhaps by collapsing          lake. To the left (north end of the pit) the layers of tuff-breccia                                                                          for the fossils of plants and animals they contain. Elsewhere in                                                                              Top. Subsequently it was shifted about three and one-half
into voids created by eruptions of later lavas.                        curve around the pit, giving a hint of the inner parts of the volcano                                                                        the Preserve, bands of more intense red are found at the tops and                                                                             miles northwest by movement along Wildcat Fault. That
                                                                       walls that originally stood above the surrounding terrain as a                                                                               bottoms of lava flows. In such cases iron was oxidized and                                                                                    makes a total of four volcanoes.

								
To top