Big Southern Butte, 25 miles distant, frames the Blue Dragon Flow, whose color is thought to come from cobalt-blue titanium that surfaced as magma was rising from the earth’s mantle. Sixty different historic lava flows punctuate Craters of the Moon National Monument, which was expanded in 2000 to a size approaching that of Rhode Island.

ARCO, Idaho —

In the middle of a vast lava plain in the heart of southern Idaho, a charcoal-colored cinder cone rises several hundred feet above the surrounding landscape — a wasteland so hostile that even Native Americans gave it wide berth.

It’s called Inferno Cone, and was so named for the fiery fountains of molten lava that once spewed from a rupture in its summit. Topping out at 6,181 feet above sea level, it is one of the most prominent and accessible features in the 750,000-acre Craters of the Moon National Monument and Preserve.

The hike to the top is steep but short, and is well worth the effort. Perhaps nowhere else in this volcanic wilderness can the geologic forces that built it be so clearly viewed.

Chief among those is the Great Rift. Composed of a series of parallel abysses, some of them more than 600 feet deep, this fissure crosses the lava lands from the Pioneer Mountains nearly to the Snake River, a stretch of 52 miles devoid of any human settlement.

Active as recently as 2,000 years ago (and now considered dormant), it deposited the basaltic remnants seen today — cinder and spatter cones, lava buttes, lava flows and lava-tube caves.

Scientists say that today’s Yellowstone National Park, 150 miles to the northeast, may someday resemble this barren scape. That’s because the “hot spot” that now underlies Yellowstone, and which is responsible for its fabled geysers and hot springs and other thermal features, once lay beneath the Snake River Plain as the earth’s mantle migrated above it.

From the rounded summit of Inferno Cone, the rift features may be seen in a line, one after another, to the west and south. To the east, 25 miles across the ocean-like Blue Dragon Flow, 7,560-foot Big Southern Butte stands like a sentinel above the Idaho National Laboratory nuclear-engineering site. North, Rocky Mountain sub-ranges reach above 12,000 feet and extend to the renowned Sun Valley resort and beyond. In all, 60 different historic lava flows punctuate this area.

‘A living timeline’

Craters of the Moon was so-named in the 1920s by geologist-explorers who suggested that its surface resembled that of the moon as seen through a telescope. After astronauts walked on the moon, the world knew that the meteor-pocked surface of earth’s satellite was no more like Idaho than green cheese. But the name had already stuck.

The nomadic Shoshone and Bannock Indians traveled on a couple of well-worn foot trails across the plain, connecting their Snake River salmon-fishing grounds with the fertile Camas Prairie, where they hunted and harvested roots and fruits. Artifacts, including stone tools and arrowheads, have been found in some areas, but the tribes appeared to have moved as quickly as possible through this unforgiving desert to the foothill region at the north end of the lava fields. After all, ground temperatures can reach 150 degrees in summer, and they are often sub-zero in winter.

By the 1850s, the foothill trails had come into use by pioneer emigrants as an Oregon Trail alternative known as Goodale’s Cutoff, a route that now is traced by U.S. Highways 20 and 26.

But it was the 20th century before the U.S. Geological Survey undertook expeditions to gain more knowledge of the lava plain. In 1924, Robert Limbert, a Boise taxidermist-turned-author and lecturer, wrote a National Geographic article (“Among the Craters of the Moon”) that described an arduous south-to-north trek along the length of the Great Rift. His work was a major factor in President Calvin Coolidge’s proclamation of Craters of the Moon as a national monument, under the administration of the National Park Service, later that same year.

Its boundaries were subsequently adjusted and expanded. In 2000, adjacent Bureau of Land Management lands surrounding the southern section of the Great Rift were incorporated to increase the size to nearly that of Rhode Island. Early this year, Secretary of the Interior Ryan Zinke, reviewing a Trump Administration proposal to reduce the size of national monuments, assured Idahoans that this preserve will not be threatened. “As a former geologist, I realize Craters of the Moon is a living timeline of the geological history of our land on the Great Rift,” he said.

The park loop

The main visitor entrance to Craters of the Moon is off U.S. Highway 20, which links the Idaho cities of Mountain Home and Idaho Falls. The visitor center is about an hour’s drive southeast of Sun Valley, but the nearest town with motels and restaurants is Arco, 18 miles to the northeast.

There are 6 miles of paved road within the non-wilderness section of the park, half of that in a loop drive. The entire road system may easily be driven in an hour, including brief stops. I recommend taking at least half a day, allowing time to hike short trails to outstanding features. I planned two half-days, overnighting in Arco to view the volcanic landscape in different hours, and with both late-afternoon and morning light.

I started my exploration watching a short introductory film, and looking at exhibits on geology and natural history, at the visitor center. There’s a bookstore here, and information on ranger-led walks and summer evening programs. Nearby, a well-kept campground welcomes outdoors lovers on a first-come, first-served basis.

A quarter-mile trail into the North Crater Flow — at 2,000 to 2,500 years, one of the park’s youngest features — begins less than half a mile down the road. Geologists report that a thick outpouring of lava ripped open a vent on the northwest side of the North Crater cinder cone, which rises above the flow, and streamed a mile downhill. A highlight of this trail is a trio of monolithic blocks, believed to have once been fragments of North Crater that were rafted here in the flow of molten lava.

This trail is also a great place to learn something about the main types of lava, both of which have Hawaiian names. Relatively smooth pahoehoe (meaning “ropy”) was created by highly fluid rock, flowing rapidly at a temperature of nearly 2,200 degrees. It formed a crust as it cooled, pulling its layers into coils and often forming lava tubes beneath. By contrast, a’a (“hard on the feet”) flows have rough, jagged surfaces. Somewhat cooler and thicker than pahoehoe, a’a tumbles slowly over a landscape as a mass of sharp, broken rocks.

A’a is particularly prevalent at the Devil’s Orchard, another mile down the park road. Here, an accessible half-mile nature trail winds through a setting of rock and cinder, accented by larger lava fragments from the North Crater wall. An early 20th-century preacher saw only “a garden fit for the devil,” according to local lore, but modern scientists embrace it as a geological laboratory. Interpretive signs describe conservation efforts and past failures in reducing human impact on the lava flows.

Fiery remnants

It’s another mile on the loop road to the parking area at the foot of Inferno Cone, with its view of the craters and cinder cones atop the Great Rift. A single large limber pine stands near the cone’s rounded summit; from here, it’s easy to spot the line of tamarack painting the northern slope of Big Cinder Butte, 2 miles south and one of the world’s largest basaltic cinder cones.

The Blue Dragon Flow, which may be seen reaching many miles to the east, is a phenomenon so unique that a friend asked: “Is that a lake?” In fact, its color is thought to come from cobalt-blue titanium that separated and surfaced as magma was rising from the earth’s mantle. Some early visitors thought it resembled the scales of a dragon.

Far more distinct are the series of spatter cones a quarter-mile southwest of Inferno Cone. Sometimes described as “miniature volcanoes,” they formed along the Great Rift fissure when viscous blobs of molten lava fell together after being launched into the air during the last set of eruptions. Short trails enable views into dramatic craters.

The parking area for the spatter cones also serves as one end of the 1.8-mile North Crater Trail, which winds past the so-called Big Craters and back to the parking lot for the original flow trail.

On the east side of the park’s main loop road, 1½ miles from the spatter cones, is the Caves Area. Each person who requests a cave permit from the visitor center is asked to affirm that they carry nothing that has accompanied them into a cave in the past 12 years, including clothing, shoes and flashlights. The National Park Service is doing everything in its power to stymie the spread of the deadly white-nose syndrome fungus among easily infected bats.

Caves accessible from a 0.8-mile trail are actually lava tubes: Dewdrop, Boy Scout, Beauty and Indian Tunnel. Their entrances were revealed with the collapse of ceilings that concealed hardened channels left when rivers of hot lava drained away. Indian Tunnel is perhaps the most interesting, an 800-foot passage with several ancient stone circles outside. They may have been built by the Shoshone, who used the caves for shelter and water sources on their nomadic routes.

More to see

From the south end of the Craters Loop Road, a 1.2-mile spur ends at a trailhead with links into the vast wilderness of the national monument and preserve. The shortest of them, the mile-long Tree Molds Trail, extends to cylindrical molds of lava-charred trees standing in forest-like isolation. The hardened molds, which remained after the wood burned away and rotted, range from a few inches to more than a foot in diameter.

The 1.8-mile Broken Top Trail circles a cinder cone with a “Big Sink” viewpoint, while the Wilderness Trail extends about 6 miles along the Great Rift to a peak known as The Sentinel. Both trails pass through a range of lava formations, including cascades and squeeze-ups. Lava cascades occurred when molten lava burst through cracks in natural rock dams, while squeeze-ups were forced like toothpaste through the hardened surface of flows where they were buckled by the internal pressure of magma.

Especially in spring, colorful wildflowers carpet this seemingly barren landscape. More than 300 plant species have been identified here, from tiny monkeyflowers, their magenta blossoms ubiquitous after snowmelt in Devil’s Orchard, to dwarf buckwheat, its miniature cluster of cream-colored, petal-like leaves attached to a root system that may dig 3 feet into cinder.

And there’s lots of other life here. Naturalists have counted 44 mammals, large and small, and 148 species of birds, along with amphibians, reptiles and more than 2,000 types of insects, some of which — like the blind lava-tube beetle — never see the light of day. Mammals, in particular, must adapt to survive the hostile environment. Some are nocturnal; others burrow into crevices or hibernate not only through the winter, but also through the high heat and extreme drought of mid-summer.

Although my early October visit yielded few wildflowers and only a few creatures, mainly raptors and mule deer, I was glad to visit when I did. Mid-summer would not have been pleasant. But I may look forward to a visit in the spring, when the wildflowers rush forth, or even in winter, when the park road (closed beyond the campground from November to April) welcomes cross-country skiers and snowmobilers.

About Arco

Craters of the Moon’s unlikely gateway community is Arco, a settlement of about 1,000 people whose other claim to fame is that it was the world’s first town to be entirely lit by nuclear energy. That occurred in July 1955 as a one-hour experiment conducted by the Atomic Energy Commission. It was powered by a nuclear reactor at the nearby National Reactor Testing Station (NRTS), now the Idaho National Laboratory.

There’s not much to see in this small junction town. Its most distinctive sight is Number Hill, a steep bluff upon which every Butte County High School graduating class since 1920 has painted its class number on the rocks. Through 2017, that makes 98 numbers.

I spent a comfortable night in the modest Lost River Motel, painted in bright Caribbean colors to stand out from the bleak surrounding desert. My meals at the family-operated El Mirador II Mexican restaurant and at the community-favorite Golden West Café were not especially memorable, but they were satisfactory.

The Big Lost River, which flows through Arco, might indeed be considered a “lost” river. Rising on the flank of 12,662-foot Borah Peak, Idaho’s highest mountain, it disappears into the Lost River Sinks east of Arco, feeding an aquifer that eventually reaches the Snake River. Here is located the 890-square-mile Idaho National Laboratory, formerly the Idaho National Engineering and Environmental Laboratory (INEEL), a facility dedicated to developing peacetime uses of nuclear power. Beginning in 1949, 52 reactors (the most on the planet) were built on this reserve, a handful of them still in operation.

For summer visitors, the site of greatest interest is Experimental Breeder Reactor I, 18 miles east of Arco off Highway 20. On an early December afternoon in 1951, this reactor — housed in a nondescript brick building — was the world’s first to produce electric power (in a row of four light bulbs) with atomic energy. It’s now a National Historic Landmark. Free tours are offered Memorial Day weekend through Labor Day.

— John Gottberg Anderson can be reached at janderson@bendbulletin.com.

If you go

(All addresses in Idaho)

EXPENSES

Driving miles, Bend to Arco, Idaho, 1,024 miles (round trip) @ $2.60/gallon $106.50

Lodging and meals en route (two nights with meals), Boise $300

Admission, Craters of the Moon National Monument $15

Dinner, El Mirador II, Arco $15

Lodging (one night), Lost River Motel, Arco $44.07

Breakfast, Golden West Café, Arco $10

TOTAL $490.57

INFORMATION

Bureau of Land Management. Shoshone Field Office, 400 W. “F” St., Shoshone; www.blm.gov, 208-732-7200.

Craters of the Moon National Monument and Preserve. 1266 Craters Loop Road, Arco; www.nps.gov/crmo, 208-527-1300.

LODGING

D-K Motel. 316 S. Front St., Arco; www.dkmotel.com, 208-527-8282. Rates from $45

Lost River Motel. 405 Highway Drive, Arco; www.lrmotel.com, 208-527-3600. Rates from $40

A Wood River Inn. 603 N. Main St., Hailey; www.woodriverinn.com, 208-578-0600. Rates from $110

DINING

El Mirador II. 450 W. Grand Ave., Arco; 208-527-4472. Lunch and dinner, Monday to Saturday. Moderate

Golden West Café. 2431 U.S. Highway 20, Arco; 208-527-8551. Three meals, Monday to Saturday. Moderate

Pickle’s Place. 440 S. Front St., Arco; picklesplacerestaurant.com, 208-527-9944. Three meals every day. Moderate