Southern Idaho’s Snake River Plain represents the track of the Yellowstone Hotspot. Yellowstone is currently located in northwestern Wyoming. In the geologic past, the center of Yellowstone volcanism was in southern Idaho, and before that, it was located in southeastern Oregon.

Eight separate, large, dark-colored lava fields cover portions of the modern Snake River Plain: Shoshone Lava Field, Craters of the Moon Lava Field, Wapi Lava Field, Kings Bowl Lava Field, Cerro Grande Lava Field, North Robbers Lava Field, South Robbers Lava Field, and Hell’s Half Acre Lava Field. These lavas erupted during the late Pleistocene and Holocene, well after the Yellowstone Hotspot “migrated” to the northeast. The lavas are so young that little vegetation covers them. Portions of the Snake River Plain's basaltic lava fields have been designated as Craters of the Moon National Monument. The flows & cones in the Craters of the Moon Lava Field range in age from ~15 ka to ~2 ka. The landscape is harshly beautiful and provides an excellent opportunity to closely examine terrestrial basalt volcanism.

Seen here is a portion of the North Crater Flow, which erupted from a moderately small volcano called North Crater Cinder Cone. About 2,200 to 2,400 years ago, the volcano erupted basalt lava, which spread out, cooled, and solidified.

This is a "squeeze-up" - a shallow subterranean, lava-filled conduit experienced sufficient pressure to cause cracking of surface rocks. Lava emerged from the cracks to form these distinctive bulbous structures.

Stratigraphy: North Crater Flow, Craters of the Moon Lava Field, upper Holocene, ~2.2 to 2.4 ka

Locality: trailside, North Crater Flow Trail, Craters of the Moon National Monument, northern Snake River Plain, southern Idaho, USA