Craters of the Moon National Monument embraces some 54,000 acres of lava country and a small portion of the Pioneer Mountains in southern Idaho. The climate here is semi-arid. Elevation ranges from 7,700 feet to 5,300 feet. The elevation at the monument's headquarters is nearly 6,000 feet. The weather is prone to extremes--hot, dry, and windy summers are followed by cold, dry, and windy winters. Most of the monument's precipitation, seventeen inches a year, falls as snow and drifts across the volcanic landscape. In the clear and rarified air of the high desert, sunlight seems to almost be absorbed by the dark flows and formations, casting all things in shadow. At other times, especially in the morning and evening, light glances off the chaos of twisted, broken, and billowed lava terrain in an array of captivating colors.
Running across the monument's northwestern corner, U.S. Highway 20-26-93 links Craters of the Moon to the population centers of Idaho Falls, Twin Falls, and Pocatello, all of which are some two hours away. The highway also routes tourists between Yellowstone National Park and Sun Valley, two popular destinations and the sources of many monument visitors.
Craters of the Moon occupies land in two counties. Some 13,300 acres lie within Blaine County, and some 40,200 acres lie within Butte County. Butte County, a rural area, contains the small community of Arco, the nearest town to the monument.
Arco, the county seat, is eighteen miles northeast of the monument, offers a full range of services, and is considered the gateway town to Craters of the Moon.
President Calvin Coolidge signed the proclamation establishing the monument on May 2, 1924. According to that proclamation, Craters of the Moon's purpose is to preserve an area of unusual scientific and educational value and interest
which contains a remarkable fissure eruption together with its associated volcanic cones, craters, rifts, lava flows, caves, natural bridges, and other phenomena characteristic of volcanic action; and...has a weird and scenic landscape peculiar to itself.
Craters of the Moon is considered geologically significant because it preserves some of the world's best, youngest, and most exposed examples of basaltic volcanism in a small geographic area. Lava welled up from fissures along the Great Rift, which was designated a national natural landmark in 1971. Thirteen miles of the Great Rift lie within the monument. The Rift is the source of the Craters of the Moon Lava Field, composed of more than sixty lava flows, twenty-five cinder cones, and eight eruptive vents. The monument's boundaries enclose the northern corner of this vast field. Hardly a lifeless volcanic region, the monument is home to some fifty mammals and 150 bird species. More than three hundred plant species are native to Craters of the Moon. Surface water, however, is scarce and is found in lava depressions scattered throughout the area. Ice and snow, insulated in lava cavities, can be found throughout the year.