Cave / Karst Systems
Karst Topography is a landscape that is primarily formed by the dissolving of the underlying bedrock. It consists of such things as caves, sinkholes, dry valleys, sinking streams, springs, and seeps. When hiking parts of Bighorn Canyon National Recreation Area and coming across circular or linear depressions, there is a good chance a sinkhole or cave is beneath. Basically karst is water flowing through rocks and making the openings bigger by dissolving the rocks.
More easily dissolved rocks form the most significant areas of karst topography. These include:
Madison Limestone/Amsden Formation
Stress Fractures, Joints, And Cave Passageways
Some great examples are visible on the ridge line of the State Line Trail. If one measured the directions of these two sets of parallel lines that intersect each other at about 60 degrees or so and then compared these directions with the directions of the passageways in Bighorn Cavern (which just so happens to run in two primary directions) one would find the joint sets and the cave passageways run in the same directions.
That is because the water seeped along the cracks, dissolved the rock along the cracks, and thus forming the passageways along the cracks. And as the caves formed after the joints were made - and they were made from the uplift which started about 70 million years ago - most of the caves which follow the joints were formed after the start of the uplift. To complicate things a little, some of the cave passageways have been caves twice: post 350 million years ago and post 70 million years ago.
Visiting Bighorn Cavern
Bighorn Cavern contains a decent variety of stalactites, stalagmites, columns, soda straws and bacon, but the really outstanding feature is the variety of crystal formations. White gypsum flowers, aragonite needles, epsomite crystals in fragile curls, and calcite crystals decorate the cave.
Other Caves At Bighorn Canyon
Horsethief Cave and Natural Trap Cave are among the many nearby caves found in the Madison Limestone. Over 90% of the caves in Montana are found in limestones of the Madison Group. Boaters often spot an arch named Eye of the Eagle 2,000 feet above the lake in Bull Elk Basin and never realize that it is the shortest cave in the park. The rest of the surrounding cave eroded away a long time ago.
Did You Know?
On August 1, 1867, a haying party of 25 soldiers and civilians held off the attacks of over 800 Sioux and Northern Cheyenne warriors in the hayfields 2 ½ miles northeast of Fort Smith. The outcome was a draw. The incident became known as the Hayfield Fight. More...