Craters of the Moon National Monument
http://www.id.blm.gov/craters/
http://www.nps.gov/crmo/
The monument is a geologic wonder cast in a wild and remote landscape. Its central focus is the Great Rift, a 62-mile long crack in the earth's crust. The Great Rift is the source of a remarkably preserved volcanic landscape with an array of exceptional features. Craters, cinder cones, lava tubes, deep cracks, and vast lava fields form a strangely beautiful volcanic sea on central Idaho's Snake River Plain.
Volcanic eruptions first occurred at Craters of the Moon about 15,000 years ago. The most recent eruptions ended about 2,100 years ago and were likely witnessed by the Shoshone people. A Shoshone legend speaks of a serpent on a mountain who, angered by lightening, coiled around and squeezed the mountain until liquid rock flowed, fire shot from cracks, and the mountain exploded. The volcanic area now lies dormant, but its eight eruptive periods formed 60 lava flows which traveled as far as 45 miles from their vents. Some of the lava flowed around areas of higher ground, forming isolated islands of vegetation called "kipukas". Today, these kipukas provide a window on the vegetation communities of the past. They contain some of the last pristine vegetation in the Snake River Plain, including 700-year-old juniper trees and relic stands of sagebrush and native bunchgrass.
http://www.nps.gov/crmo/cavetrail.htm
They have a "Cave Trail"
The caves area contains many stark contrasts: searing heat on the black surface versus the cool of the cave interiors, roaring afternoon wind versus the dampened stillness below ground, brilliant light and expansive views versus the enclosed darkness of the lava tubes. The drama of these contradictions draws people into this strange world.
Help to Preserve the Caves
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Please do not leave any trash in the caves. There is a trash can located in the parking lot. Remember that all cave features are fragile and irreplaceable. Do not remove any rocks or other objects from the caves area.