Craters of the Moon National Monument and Preserve was millennia in the making.

The 618-square-mile lava field underlying the attraction near Arco, Idaho, was formed during eight major periods of countless eruptions between 2,000 and 15,000 years ago.

No volcanoes were involved in the process. The hardened lava was generated solely by seepage and spoutings through the Great Rift, a series of deep cracks in the Earth’s crust, aided by the occasionally earthquake and other tensional geological forces.

The next eruptive event — speculated to occur within the next 100 to 900 years — is expected to spew more than one cubic mile of magma onto the Craters of the Moon Lava Field.

For now, all is quiet, at least on a surface that, implicit in the attraction’s name, evokes an otherworldliness, one whose “eerie beauty” and barren solemnity belies the subterranean processes roiling beneath the feet of visitors.

The national monument was created by executive order on May 2, 1924. Upon signing his order, President Calvin Coolidge said, “This area contains many curious and unusual phenomena of great educational value and has a weird and scenic landscape peculiar to itself.”

The monument was significantly expanded by presidential proclamation in 2000. The portions, then administrated by the National Park Service, were designated Craters of the Moon National Preserve in 2002. The area, which spans five counties, is currently cooperatively managed by the National Park Service and Bureau of Land Management.

The lava formations take various forms:

• Lava beds/fields: lava, sometimes several layers deep, that cooled down and ossified while sliding down an incline or seeping through a fissure

• Spatter cones: accumulations of lava thrown into the air from a geological vent and falling back to earth around the eruption’s location

• Lava tubes: natural conduits of cooled rock through which lava once flowed

• Lava caves: geological cavities formed by surface solidification of lava flows during the last stages of their activity

• Pit craters: depressions formed by the sinking or collapse of the surface lying above a chamber carved by subterranean lava activity

Tourists may investigate many of the preserve’s features by car along the 7-mile loop road or during guided or individual hikes along the trailheads, which also serve as cross-country skiing courses during the winter.

Despite the ostensibly sullen barrenness of the lava expanses, the area bristles with flora and fauna that have adapted to routine summer soil temperatures of 150 F and extremely harsh aridity.

Botanists have catalogued 375 species of plants, including wildflowers, which bloom from early May to late September, that survive through the strategies of drought tolerance, avoidance and escape. The extensive root system of the prevalent dwarf buckwheat — 3 feet wide for the 4-inch-tall flowering plant — encourages the natural precise formation of evenly spaced vegetation that replicates deliberate plotting by a human gardener.

Biologists and park rangers have recorded 2,000 species of insects, eight of reptiles and one amphibian, 169 birds and 48 mammals, many of which are nocturnal. The extent of activity for many of the animals varies with the seasons.

Night brings its own rarefied beauty. The remote expanse, shielded by its inhospitable ruggedness against manmade light pollution, has been designated as an International Dark Sky Park, defined by the International Dark Sky Association as “a land possessing an exceptional or distinguished quality of starry nights and a nocturnal environment that is specifically protected for its scientific, natural, educational, cultural heritage and/or public enjoyment.”

The association noted the Craters of the Moon Monument and Reserve “sits at the edge of one of the largest remaining ‘pools’ of natural nighttime darkness in the lower 48 U.S. states.”

Enticed by accounts from fur trappers about “strange things they had seen,” Robert Limbert explored the region in the 1920s and wrote a series of newspaper and magazine articles to increase public awareness of the area. In a 1924 issue of National Geographic, Limbert solidified the name Craters of the Moon and described its Blue Dragon Flows:

“It is the play of light at sunset across this lava that charms the spectator. It becomes a twisted, wavy sea. In the moonlight its glazed surface has a silvery sheen. With changing conditions of light and air it varies also, even while one stands and watches. It is a place of color and silence.”

The Robert Limbert Visitor Center is located near the monument’s entrance on U.S. Highway 20/26/93 midway between Arco and Carey, Idaho. The facility includes exhibits, educational films and a natural history bookstore.

The center’s hours are 8 a.m. to 4:30 p.m. daily. The building is closed Thanksgiving, Christmas and New Year’s Day.  For more information, call (208) 527-1300 or (208) 527-1335 or visit www.nps.gov/crmo.