Craters of the Moon Wilderness, Idaho

The 43,243 acres of Craters of the Moon Wilderness are managed by the National Park Service as part of the Craters of the Moon National Monument (715,000 acres) in eastern Idaho. This is a large roadless area because of the broken-ness of the topography: more than 2,000 years ago, large amounts of basalt lava were distributed across about 700 square miles of Idaho along the Great Rift. There are numerous hidden ice caves and lava tubes among all the spatter cones and cinder cones in the Craters of the Moon Wilderness. Because of the ruggedness of the topography and the surface material, hiking is hard and horseback riding is not recommended. Compasses don't work among the lava flows because of the level of magnetism inherent in the rock. Topographic maps are essentially useless because this is an area of large lava flows: the extreme level of microtopography just doesn't appear at the scale maps are done in. If you are out here in a fog, stay put: you can't see anything and the ground is so incredibly broken...

The lava flows in this area along the Great Rift (a 62-mile-long crack in the surface of the Earth) began probably 15,000 years ago. The last eruptions were probably witnessed by the Shoshone about 2,100 years ago. There were 8 major eruptive periods in between, with more than 60 separate lava flows, some running as long as 45 miles from the vents they emerged from. In some areas, the lava flowed around pre-existing higher ground and trapped communities of vegetation in those areas above the hot lava. On some of these hills you'll find sagebrush and native bunchgrass relics with some 700-year-old junipers.

Some eruptions at Craters of the Moon were gassy, and bubbly rocks were ejected hundreds of feet into the air, often falling back to ground and forming cinder cones around the vents. Less gassy eruptions resulted in simple flows of sheets and rivers of peanut-butter-consistency olivine basalt which inched its way along over the surface, twisting, congealing and breaking into jumbled masses of jagged rock. You'll also find spatter cones and lava tubes scattered among the 25 cinder cones and eight fissures and fissure systems. USGS scientists have deterrmined that the main lava flows seem to occur on average every 2,000 years (meaning it's about time once again). And between 6,000 and 8,000 years ago, the lava flows almost doubled in volume from what they had been previously.

The Great Rift volcanic zone is a two-mile-wide zone of linear surface cracks that tend to run northwest to southeast (N35°W) across most of the eastern part of the Snake River Plain. This whole area of Idaho is contained within the Picabo Volcanic Field. This is also an area where there is no surface water.