Craters of the Moon

A vast lava field on Idaho's Snake River Plain, where cinder cones, lava tubes and spatter cones resemble the lunar surface—a striking stop en route west from Yellowstone.

Craters of the Moon National Monument and Preserve lies on the northern edge of the Snake River Plain in south-central Idaho, a basalt lava field covering about 2,900 km². Between roughly 15,000 and 2,000 years ago, repeated eruptions along the "Great Rift" fissure zone created cinder cones, spatter cones, lava tubes and tree molds. In the 1920s the black wasteland was described as "like the surface of the moon," and Apollo astronauts later trained here in geology.

The heart of a visit is the seven-mile one-way Loop Road from the visitor center, which passes in turn the North Crater Flow, Devils Orchard, Inferno Cone, Spatter Cones and Big Craters, the Caves Area and the Tree Molds trail. Most sights are a few minutes' to half an hour's walk from the parking areas; you can see the highlights in half a day, but allow a full day for caving and hiking. A free cave permit from the visitor center is required before entering the lava tubes. Entry is about $25 per vehicle (valid 7 days), and the America the Beautiful annual pass is accepted.

The best season is May–October; the Loop Road is usually open from late April to November, and after it closes in winter it becomes a cross-country ski and snowshoe route. In summer, ground temperatures can exceed 60°C during the day, so visit early or late, bring plenty of water and sun protection—there's almost no shade—and be ready for big day-night temperature swings at this elevation. The monument is also an International Dark Sky Park, and the Milky Way is visible on clear nights.

You'll need a car: it's about 1.5 hours east of Sun Valley and 3 hours from Boise, and about 1.5 hours west of Idaho Falls, making it a popular stop between Yellowstone and Boise/Sun Valley. The park has only one first-come, first-served campground; most lodging is in the town of Arco, about 30 km northeast. About 45 km east, the Experimental Breeder Reactor-I museum is open free in summer and makes an easy side trip.

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