Mystery Cave is a maze of fragile
mineral formations, dripping water, and mirrored pools
U N D E R the rolling hills of south-
eastern Minnesota is a remark-
able s p a c e — 1 2 miles of m a p p e d
Geologists believe that most of this
dissolving took place below the water
table. Over time water levels dropped,
passages known as Mystery Cave. It leaving the upper passages dry. After
is the state's largest known natural the water levels dropped, ground-
limestone cave and the 34th longest water dripping into the cave redepos-
cave in the United States. Last year ited dissolved limestone, or calcite,
the Department of Natural Resources in a variety of white, brown, and
bought and reopened the cave near orange formations, or "speleothems.
Spring Valley as part of Forestville Many are still being formed.
State Park. Typical formations in Mystery Cave
Visitors to Mystery Cave see fasci- include icicle-shaped stalactites drip-
nating geologic formations and learn ping from the ceilings and stalag-
about the history and geology of this m i t e s p o k i n g u p f r o m t h e floor;
underground natural resource. Caves, flowstone, calcite d e p o s i t s f o u n d
sinkholes, blind valleys, u n d e r - where thin sheets of water flow over
ground streams, and springs are found rocks; rimstone dams, rings formed
in s o u t h e a s t e r n M i n n e s o t a w h e r e a r o u n d overflowing mineral-water
limestone bedrock has dissolved over basins; and clusters of mineral depos-
h u n d r e d s of t h o u s a n d s of y e a r s . its called cave "popcorn."
Limestone dissolves when rain picks Mystery also has curious wormlike
up carbon dioxide from organic soil, stalactites, called helictites, and
forming carbonic acid. botryoidal cones. Some of the cones
In the case of Mystery Cave, this are nearly 6 feet high. They form in
weakly acidic g r o u n d w a t e r p e r c o - underground pools. Visitors can see
lated down into the limestone through a blue pool studded with these cones.
a series of vertical cracks and joints.
Over time these joints enlarged and S c u l p t e d Walls. M y s t e r y C a v e
formed the cave. formed near the contact point of two
MAY-JUNE 1989 37
In rock garden, rimstone dams form ring around overflowing mineral-water basin.
separate layers of rock. Cave pas- it r e - e m e r g e s at Seven Springs it is
sages in the u p p e r level are boxlike the ideal t e m p e r a t u r e for trout.
with flat ceilings. T h e lower levels M y s t e r y Cave also has s e v e r a l
feature d e e p crevices, sculpted walls, u n d e r g r o u n d pools. O n e called Lily
and vaulted ceilings. Both layers of Pad Lake is nearly 6(X) feet long. Most
rock exhibit a variety of marine fossils. of the pools exhibit delicate and col-
T h e cave has a complex under- orful formations.
ground stream system. T h e South Caves do not s u p p o r t the diversity
Branch of the Root River sinks into of animal life found above ground, but
crevices, travels through the cave, and Mystery Cave does provide impor-
re-emerges about 1.5 miles away at tant habitat for a few species, most
Seven Springs. D u r i n g a normal n o t a b l y bats. Bats use t h e cave
summer, m u c h of the stream b e d t h r o u g h o u t t h e year.
b e t w e e n these points is b o n e dry. As All four species of h i b e r n a t i n g bats
the water travels through the cave, native to Minnesota—little brown bat,
which has a year-round t e m p e r a t u r e n o r t h e r n myotis, big brown bat, and
of about 48 degrees, it is cooled in eastern p i p i s t r e l l e — u s e the cave in
summer and warmed in winter. When winter. Mystery Cave is o n e of the
few natural winter residences for bats
Mark White is park manager, Forestville in Minnesota.
State Park, Preston. People began visiting Mysteiy Cave
38 T H E MINNESOTA VOLUNTEER
long before the DNR opened it to I , A
tourists. T h e original Mystery Cave
(Old Mystery) was located several
hundred feet from the present day
Mystery Cave. According to local
legend, area farmers used it to hide
horses from Union troops during the
A group of local men leased the site
and opened it for commercial cave
tours in 1935. During the early years
of operation, the cave was named.
According to Clarence Prohaska, who
later owned Mystery Cave, he and a
crew were working in Old Mystery
doing improvements. Prohaska
remarked that it was a mystery why
anyone would want to work in such a Beyond commercial tour route, author
place, hence the name Mystery Cave. squeezes through wild cave passage.
U n e a r t h i n g an E n t r a n c e . In Feb- new Mystery Cave and the adjacent
ruary 1937 Joe Petty was returning park. Along with his brother Donald
home on foot from digging a grave at and brother-in-law Cardinal Bacon,
a nearby cemetery. At the time, he Prohaska redeveloped the cave for
was managing the tour operation at tours and established a thriving busi-
Old Mystery and lived in a house on ness in competition with Niagara
the grounds. He noticed a spot on the Cave, another commercial cave, about
slope near the river where the snow 20 miles away near Harmony, Minn.
h a d m e l t e d a n d t h e g r o u n d was Prohaska made the cave his life's
muddy. He moved some rocks work, promoting its exploration. In
enlarging a small hole — the entrance 1963 he became one of the founders
to present-day Mystery Cave, which of the Minnesota Speleological Sur-
was more spectacular than the old. vey, t h e s t a t e ' s p r i n c i p a l c a v i n g
Petty helped develop the new cave organization.
for tours. In the early 1960s, with the open-
T h e n , in 1942, a s e r i o u s (food ing of Interstate 90 and the resulting
inundated grounds, buildings, and reduction of traffic on nearby U.S.
cave entrances. A layer of silt and mud Highway 16, tourism took a down-
filled much of the cave. The flood put turn. Prohaska sold the operation in
an end to tours for several years. 1977 to Neil Davie, a fellow Speleo-
In 1947 Prohaska purchased the logical Survey member.
MAY-JUNE 1989 39
discovered in mid-
walls, deep crevices,
and vaulted ceilings.
Explorers have found
a variety of marine
fossils in both the
upper and lower
levels of the cave.
In early 1985 the D N R got word m e n t officials, cavers, a n d neighbors
that the cave was for sale. Bill Mor- f o r m e d an advisory c o m m i t t e e . In
rissey, t h e n D N B regional adminis- 1987 the Legislature passed a bill that
trator for southeastern Minnesota and a d d e d the cave to Forestville State
now director of D N R Division of Parks Park.
and Recreation, and other D N R T h e D N R has four basic goals for
regional e m p l o y e e s recognized the managing Mystery Cave: preserva-
cave as an o u t s t a n d i n g natural and tion, public tours and education, rec-
recreational resource in need of pro- reational caving, and continued
tection. A proposal was developed to research.
include the cave in the state park sys- Preservation
tem to protect it and allow tours to Many of the cave's geological resources
continue. are n o n r e n e w a b l e . Cave formations
Local b u s i n e s s p e o p l e , g o v e r n - grow at different rates d e p e n d i n g on
40 THE MINNESOTA VOLUNTEER
m a n y v a r i a b l e s , b u t g r o w t h is scientists can trace the past. In Mys-
extremely slow in human terms. Rich tery Cave, sediments reflect climatic
Lively of the Minnesota Geological c h a n g e s above g r o u n d . T h e sedi-
Survey has d e t e r m i n e d that cave for- ments mark the advance and retreat
mations in Mystery are from about of glaciers and the rise and fall of water
12,000 to 160,000 years old. levels.
Not only are cave f o r m a t i o n s The undisturbed pattern of sedi-
impossible to replace, but many also ments needed for study can be quickly
are extremely delicate. For example, destroyed by walking on them. Fine
soda-straw stalactites break at the sediments tracked as mud or dis-
slightest touch. Rimstone dams are turbed as dust can easily end u p in
thin, fragile calcite rims. Floating pools and on flowstone and other
calcite rafts are thin plates of mineral formations.
that form on the surface of pools. They Even cave walls need protection.
are held u p by the surface tension of Natural colors and textures can be
water and resemble little sheets of ice. altered simply by touching.
Possibly the most fragile formation is Cave life is sparse compared with
gypsum frostwork, fine needlelike life found on the surface. Most plants
crystals that form in drier parts of the cannot grow without sunlight. Cave
cave. insects and other creatures must rely
Because they are not pretty, cave on food that washes into the cave or
sediments are often overlooked as a is b r o u g h t in b y o t h e r a n i m a l s .
geological resource. Through them, Because of this, cave organisms lead
1 Entrance 2 0)
Horizontal scale (feet): q 600 1200
Cross-section of Mystery Cave. South Branch of the Root River enters near first
entrance and travels 1.5 miles through the cave before re-emerging at Seven Springs.
Original diagram courtesy of Jodi A. Milkse.
MAY-JUNE 1989 41
such as these soda-
break at the slightest
touch. They are irre-
formations in Mystery
Cave have grown very
slowly over the past
12,000 to 160,000
a precarious existence and may he Cave tour guides tell visitors how
sensitive to even slight e n v i r o n m e n - to help protect the cave. They remind
tal changes. t h e m not to touch formations and
Bats also are sensitive to disturb- surfaces inside the cave and not to eat,
ance, especially from October through drink, smoke, or chew gum or tobacco
A p r i l , w h e n t h e y h i b e r n a t e . In d u r i n g cave tours. Some fragile areas
unprotected caves, human activity has are off-limits to everyone.
had a devastating impact on bats. Of particular concern inside the
T h e c o m p l e x i t y of p r o b l e m s in cave is the lighting system. As out-
preserving Mystery Cave b e c o m e s dated lighting is replaced, care m u s t
more u n d e r s t a n d a b l e w h e n we think b e taken so that lights do not dry out
of the cave as an ecosystem. Although formations. Improper lighting also can
separate from the surface environ- stimulate unnatural moss and algae
ment, the cave is intimately con- growth.
n e c t e d to it. B o t h s u r f a c e a n d Tours and Education
underground environments require " I n t e r p r e t i v e tours will b e t h e high-
resource m a n a g e m e n t . light of m a n a g e m e n t at Mystery,"
E n t r a n c e design must not change Warren N e t h e r t o n , the state's first
airflows, which might dry u p forma- cave specialist, says. "We want to give
tions. E n t r a n c e s must b e secure from tourists m o r e than just a walk to see
vandals, yet accessible to bats. pretty things. We would like to have
Surface development and land use, t h e m c o m e away from t h e cave with
such as parking lots, sewage systems, a b e t t e r u n d e r s t a n d i n g of t h e cave
and feedlots, can affect the cave. Even environment and its relationship with
the impact of vegetation on the sur- the outside world." For instance, the
face must b e considered. cave is an ideal place to learn about
42 T H E MINNESOTA VOLUNTEER
the i m p o r t a n c e of g r o u n d w a t e r and have b e e n instrumental in p r o m o t i n g
the n e e d to protect it. cave conservation. Currently, guide-
In its first s u m m e r as a park oper- lines and policies are being estab-
ation, t h e cave had m o r e than 11,000 lished to h e l p e n s u r e c o n t i n u e d
visitors. At p r e s e n t , only one cave protection of the wild portions of
e n t r a n c e is usable. Park officials h o p e Mystery.
to p r o v i d e w h e e l c h a i r a c c e s s b y Continued Research
redesigning a second e n t r a n c e to the Many educational goals of t h e cave
cave. i n t e r p r e t i v e p r o g r a m d e p e n d on
Recreational Caving research. Over the last several years,
Of the m o r e than 12 miles of passages Mystery Cave research projects have
known in Mystery Cave, less than two i n c l u d e d work on cave geology,
m i l e s is c o m m e r c i a l l y d e v e l o p e d . hydrology, and bats. "We h o p e to use
Exploring t h e u n d e v e l o p e d passages t h e cave as a living laboratory con-
is known as caving, or spelunking. sistent with our m a n d a t e to preserve
Spelunkers crawl through tight, the cave, Morrissey, D N R Parks and
m u d d y passages and scale d e e p crev- Recreation director, says. Potential
ices, usually with little light. T h e y r e s e a r c h i n c l u d e s s t u d i e s on cave
must use special e q u i p m e n t , safety meteorology, minerals, and life in
guidelines, and conservation the cave.
practices. Park officials predict that Mystery
Not only are physical risks g r e a t e r Cave will b e c o m e one of t h e top nat-
in u n d e v e l o p e d sections of the cave, ural-resource attractions in the Mid-
but caving often m e a n s direct contact west. G u i d e d tours of Mystery Cave
with fragile resources. M e m b e r s of the are available every day from M e m o -
Minnesota Speleological Survey, an rial Day through Labor Day. For more
organization d e d i c a t e d to the explo- information, write: Forestville State
ration and study of caves, have b e e n Park, R o u t e 2, Box 128, Preston, MN
caving in Mystery since 1963. T h e y 55965. Phone:507-352-5111. •
If It Ain't Broke, Don't Fix It
"/FTHli land m e c h a n i s m as a w h o l e is g o o d , then e v e r y part is g o o d , w h e t h e r w e
understand it or n o t . " —Aldo Leopold
Aerial View Does Justice to Rivers
"FTIVEKS ARE perhaps the only physical features of the world that are at their best
from the air. Mountain ranges dwarf to anthills; seas lose their horizons. But
rivers stretch out serenely ahead as far as the eye can reach. Rivers are seen in
their true stature." — Anne Morrow Lindbergh, North to the Orient
MAY-JUNE 1989 43