BATS

Minnetonka Cave is an 

important hibernaculum 

to fi ve bat species. The 

Townsend’s big-eared 

bat (Corynorhinum 

townsendii) is of 

special concern to the 

management of the cave, 

and is a State of Idaho 

species of concern and a 

Forest Service Sensitive Species.

Townsend’s big-eared bats prefer the fi rst 300 feet inside the cave entrance for hibernation. In this area the air temperature 

is cooler than 40°F. To enhance bat habitat within the cave, a “bat door” was installed. This bat friendly door not only protects 

cave resources, but also enables all bat species to fl y through the openings in the door. It also allows cold air to enter the 

cave to provide for the thermal requirements of the Townsend’s big-eared bat. 

GUIDED TOURS

Guided tours of the cave are conducted from the second week in June until Labor Day. During this operating season, 

the cave is open seven days a week, including holidays. Tours are conducted every half hour from 10:00 a.m. to 5:30 p.m., 

and last approximately 90 minutes. There is a fee charged for the tour. The hike in and out of the cave is best described as 

strenuous (896 stairs round trip). A jacket and gloves are recommended, as the temperature in the cave is a constant 40°F.

LOCATION

Minnetonka Cave is located in southeastern Idaho, 

near the Utah-Idaho border. It is about 12 miles west from 

scenic Bear Lake, near the head of St. Charles Canyon, 

and 10 miles west of St. Charles, Idaho. The cave is 

in the Bear River Range, which is part of the Wasatch 

system of Southeastern Idaho. Although located on the 

Cache National Forest, the Montpelier Ranger District, 

Caribou-Targhee National Forest, administers the cave.

For more information, contact

Montpelier Ranger District

322 North 4th Street

Montpelier, ID 83254

208-847-0375

http://www.fs.fed.us/r4/caribou-targhee/

MINNETONKA 

CAVE

United States Forest Intermountain CaribouDepartment of Service Region Targhee

Agriculture National

 Forest

USDA is an Equal Opportunity provider and employer.

Map used with written permission from Idaho Cave Survey.

‘

23.308.415.04/04

on the

Montpelier 

Ranger District

Townsend’s big-eared bat

Bat friendly door entrance
ORIGIN

The cave’s story began some 330-350 million years 

ago, when small sea creatures lived and died in a shallow 

inland sea. Their remains formed calcite sediment layers 

that hardened into limestone. Then about 50-80 million 

years ago tremendous forces were at work fracturing and 

faulting the rock. The rock was uplifted with the mountainbuilding processes and became part of the Bear River 

Range. 

Rain and snow water absorbed carbon dioxide from 

the atmosphere, the soil, and decaying plant material 

to form a weak carbonic acid solution that dissolves 

limestone rock. This solution followed the fractures until 

it reached a zone fi lled with water. The term water table 

refers to the upper surface of this saturated zone. Over 

time, the dissolving action of the weak carbonic acid 

solution along cracks and faults formed crevices, then 

tunnels, then passages, and then water-fi lled chambers 

and rooms. As the water table lowered and the valleys 

deepened, the underground chambers were drained. The 

clay and hard chert particles found in the cave are the 

residual parts of the limestone rock that did not dissolve. 

It is the drip, drip, drip of water that decorates the 

cave. Air-fi lled chambers provide ideal conditions for 

the formation of many beautiful and varied cave mineral 

deposits. How the water moves (seeping, dripping, 

fl owing), and how many crystals come out of the 

individual drops of water dictate the shape and size of 

the formations made of calcite. These formations, called 

speleothems, grow in an endless variety of shapes, from 

icicle-like stalactites, and pedestal-like stalagmites to 

columns, draperies, popcorn, and twisted helictites. Today 

the cave is still “alive” and formations continue to grow 

at varying rates as water seeps down from the overlying 

areas above the cave.

Running water played a minor role in the formation 

of the cave. Stratifi ed sands, clays and rounded pebbles 

on the cave fl oor are evidence of stream action. This 

action occurred during dryer, more recent times after 

the groundwater table dropped below the bottom of the cave. 

Clay, found throughout the cave, is from impurities in the 

limestone and remained after the lime dissolved. The sand 

and pebbles, water-washed chert nodules, are also impurities 

in limestone. Being composed of hard, insoluble materials, 

these were also deposited throughout the cave. Subsequent 

stream action wore off the edges and corners, rounding and 

polishing them.

In one of the chambers, excavation has revealed sand, 

clay, and pebbles arranged in delta-like deposits, which 

means the material was deposited in a cave lake or pool. At 

various times a number of lakes have probably occurred within 

the cave. These all disappeared as the groundwater table 

dropped.

CAVE FORMATIONS

Some of the more interesting features of the cave are the 

deposits of lime (calcite) as stalactites and stalagmites and 

drapery (pictured below). Most of these depositional features 

are very old, while others are still being formed.

STALACTITES are icicle-like formations, which hang 

from the ceiling of the cave at points where water drips from 

the ceiling. Little by little, lime is deposited and the formation 

begins. As 

this process 

is continued 

a tube is 

formed. 

Deposition 

takes place 

around 

the drop 

of water, 

which has 

descended 

the tube 

and hangs 

suspended 

at its very end. In this manner the tube continues to elongate. 

A fi lm of water fl owing down the outside of the tube leaves thin 

layers of lime so the stalactite gains in diameter as layer is 

added to layer.

STALAGMITES are formed on the fl oor of the cave by 

dripping water from the stalactites above. This formation 

grows upward.

HELICTITES are formed in a similar manner as stalactites. 

For some reason, however, they do not follow the typical 

icicle pattern. They are observed in the cave in fi shhook- and 

corkscrew-like formations.

FOSSILS

Numerous fossils of animals that lived in the tropical waters 

of the Mississippian Period are found in the ceiling and walls 

of the cave. These fossils include: horned coral, honeycombed 

coral, brachiopods, bryozoans, and crinoid stems. These 

skeletons were deposited in the warm tropical water along 

with the lime and mud in layers. Over time, the lime and mud 

layers hardened into rock by pressure and were later uplifted 

to form the Bear River Range.

DISCOVERY AND 

DEVELOPMENT

Edward Arnell of St. Charles, Idaho, accidentally found 

the cave in the early summer of 1906 or 1907. Mr. Arnell and 

others were in St. Charles Canyon constructing a sawmill. 

He went in search of meat for their evening meal and shot a 

grouse. The grouse fell at the cave entrance and, as Mr. Arnell 

went to retrieve it, he discovered the very small cave opening 

– only because of a cool breeze blowing from it.

The following day he and several others made what is 

thought to be the fi rst exploration of the cave by white men. 

It is believed that the cave’s fi rst name “Porcupine Cave” 

originated because a live porcupine and porcupine bones 

were discovered in the cave.

Local tradition honors Roy Welker, an educator and 

church leader of Bear Lake County, as the person to fi rst 

apply the name “Minnetonka” to the cave. Minnetonka is 

an Indian word meaning “falling waters,” as is suggested 

by the considerable dripping of water from the ceiling of 

the cave.

Very little public interest was shown toward the cave 

from its discovery until about 1938. During this time, 

however, extensive vandalism mutilated or destroyed 

many of the more striking and beautiful formations.

In the early days of the Works Progress Administration 

(1938), the Government undertook the fi rst development 

of the cave, constructing a trail from the St. Charles 

Canyon Road to the cave entrance. Interior paths, steps, 

and railings were installed during that period. Gasoline 

lanterns were used for light during the guided tours 

through the cave. 

Minnetonka Cave had been open for only a couple of 

years when World War II began. The cave was closed 

during the war years, and then reopened in 1947 under 

the direction of the Forest Service. In 1949, the Paris 

Lions Club was issued a special use permit to operate the 

cave. They maintained and administered the cave until 

1963. From 1964 until 1994, the Forest Service managed 

the cave as part of its Visitor Information Service 

Program. Since 1995, concessionaires have managed 

cave operations and maintenance.

St. Charles Canyon

Bacon Strip Formation

Mitch Mascaro, Herald Journal Photo