This 1,100-square-mile area contains more basaltic volcanic features than any other area of its size in the continental United States. Lava rivers once flooded the surrounding countryside, leaving vast lava fields covered by cinder cones with large central vents that were thought by early observers to resemble the craters on the moon. The volcanic activity dates back about 15,000 years, with the last eruptions occurring about 2,000 years ago.
The area's variety of surface patterns and formations is typical of the world's other basaltic lava sites. Visitors should be cautious of sharp lava formations.
A 7-mile loop drive, open from April through November, leads past the monument's main points of interest and takes about 30 minutes to complete. The view from the summit of Inferno Cone takes in the cinder cone chain along the Great Rift, a weakened zone of fissures in the Earth's crust. In winter, when the snow is sufficiently deep, the loop road is closed to vehicular traffic and is groomed for cross-country skiing and snowshoeing.
The cones formed when fountains of molten, gas-charged rock shot into the air. The frothy lava then cooled and hardened into cinders that fell around the vent, producing symmetrical cones. Numerous lava bombs, ejected blobs of less frothy lava that range from an inch to several feet in diameter, are scattered over the slopes. Big Cinder, 700 feet high, is one of the world's largest purely basaltic cinder cones.
Nearby is the Big Craters-Spatter Cone Area. These cones formed when clots of pasty lava stuck together as they fell back to Earth. A trail leads from the drive to the Cave Area, a series of lava tubes that range up to 40 feet in diameter and hundreds of feet in length. The largest is 830-foot Indian Tunnel; Boy Scout Cave has a floor of ice, even in summer. Some of the tubes can be explored; wear sturdy shoes and carry a flashlight. Permits are required and are available at the visitor center.
Other trails lead to Devil's Orchard, cinder fields scattered with fragments of a crater wall, and the Tree Mold Area, where lava slowly enveloped a group of living trees.
More than 700 species of plants and many different species of animals live in this seemingly desolate terrain. In early summer, wildflowers burst into bloom on the cinder fields and slopes of the cones.
Note: Off-road vehicles may be needed on some undeveloped dirt roads. Inquire about road conditions in advance.
A visitor center and campground-picnic area are near the entrance. Guided walks and evening programs are provided during summer months; phone for schedule. The entrance fee is $20 (per private vehicle); $15 (per motorcycle); $10 (per bicycle or per person on foot); free (ages 0-15).