Black lava flows and a low cinder cone at Craters of the Moon, with sage-covered mountains beyond
Bob Wick, BLM / CC BY 2.0 via Wikimedia Commons
Idaho · Region

Craters of the Moon & the Upper Snake

The Snake River Plain's newest ground — the lava fields of Craters of the Moon, the atomic desert at Arco and EBR-I, the Teton Dam flood, Teton Valley, and Mesa Falls on the Henrys Fork.

8 places to explore

The Upper Snake is Shoshone and Bannock country, a plain the Newe crossed for bison, camas and fish, and where the Shoshone-Bannock Tribes still hold treaty hunting rights. It is also the youngest ground in Idaho. At Craters of the Moon, lava poured from the Great Rift in eruptions between about fifteen thousand and two thousand years ago, leaving cinder cones, spatter cones and flows so bare that Apollo astronauts came here to train in 1969.

In 1949 the federal government took over the desert to the east for its reactor testing station, today's Idaho National Laboratory, and more than fifty reactors have since been built on the plain. On December 20, 1951, Experimental Breeder Reactor I lit four light bulbs with the first usable electricity any reactor had made; it is a museum now, beside US-20/26. On July 17, 1955, a reactor nearby powered the town of Arco for about an hour, the first town to take its whole supply from a reactor. In January 1961 an Army test reactor on the site, SL-1, exploded and killed three men — the only fatal reactor accident in the country's history.

Idaho Falls and Rexburg sit on the irrigated river bottoms. On June 5, 1976, the new Teton Dam collapsed as its reservoir first filled, killing eleven people and flooding Rexburg and Sugar City. Beyond, the land climbs to Teton Valley on the west side of the Tetons, to the rim of the Island Park caldera, and to the Henrys Fork pouring over Mesa Falls on its way down from Yellowstone country.

What to See in Craters of the Moon & the Upper Snake

8 places across the region, grouped by what they are.

Geology & Rock Formations

A jagged mass of black lava rising from the broken surface of a flow at Craters of the Moon

Craters of the Moon National Monument

Arco

A geologist coined the name in 1923. A Boise taxidermist carried his dog across the lava and sold the place to a president.

View details →
The trail along the crater rim of North Menan Butte, with farmland on the plain far below

Menan Buttes

Menan

Two volcanoes built where lava ran into the Snake River, and one of them open to walk around the rim.

View details →

Natural Areas

A still lake in Harriman State Park reflecting clouds and a forested ridge, dry grass and cobbles on the shore

Harriman State Park

Island Park

The Harrimans would give Idaho their ranch only when Idaho had a parks department fit to run it. The state built one.

View details →
Upper Mesa Falls pouring over its rock ledge into the Henrys Fork, with spring snow on the canyon wall

Mesa Falls

Ashton

The inn went up with a dam in mind. The dam never came, and the Henrys Fork still drops 114 feet untouched.

View details →
Rolling pale dunes crossed by tire tracks at St. Anthony, with green farmland and a distant butte beyond

St. Anthony Sand Dunes

St. Anthony

Four hundred feet of white sand, open to machines most of the year and closed to people when the elk come down.

View details →

Historic Sites

The brick reactor building of Experimental Breeder Reactor I beneath a flagpole in the desert

Experimental Breeder Reactor I

Arco

The reactor that lit four bulbs in 1951 also suffered the first accidental breeder meltdown, and two engines for a nuclear bomber sit outside.

View details →
Water cutting through the face of the Teton Dam embankment on June 5, 1976, the day it failed

Teton Dam Site

Newdale

Geologists warned that the canyon walls would leak. The warnings were softened, the dam was finished, and it never held a full reservoir.

View details →
The Warm River sliding past a timber picnic shelter and willows at Warm River Campground, a tuber standing on the grassy bank, in a Historic American Buildings Survey photograph

Warm River

Ashton

Union Pacific built the Yellowstone Branch for tourists. At the bottom of this canyon it turned the engines that pushed them uphill.

View details →

Scenic Drives through Craters of the Moon & the Upper Snake

Scenic Byway

Mesa Falls Scenic Byway: Ashton to Harriman

The old road toward Yellowstone: from Ashton's farm country down to the Warm River and up to the undammed Mesa Falls, ending at the Harrimans' Railroad Ranch.

31 mi · 1 hrs

Stories from Craters of the Moon & the Upper Snake

History

Nine O'Clock on the Third

On January 3, 1961, an Army reactor on the Idaho desert exploded and killed its three operators. Why one man lifted one rod too far is still unknown

5 min read

Craters of the Moon & the Upper Snake rewards the unhurried. Pick a base, fan out, and let the country between the headline stops surprise you.

← Explore more of Open Road Guide