The Snake River Plain

Most of Idaho is very mountainous, but most visitors would never know it because most Idahoans live on, and most used travel routes cross, the Snake River Plain, a huge largely-flat crescent that extends from near the Oregon/Idaho border on the west almost to Yellowstone National Park to the northeast. Even though the plain is the most populated part of Idaho, vast expanses on it have almost no one as the photographs below show.

At dawn, one hundred miles across the Snake River Plain to the distant Tetons. They
are on the horizon in the lower right center. © Ralph Maugha

The plain is the product of millions of years of eruptions of rhyolite, covered with more recent layers of basalt that erupted in a very fluid form from rifts as recently as about 1000 years ago. Geologists attribute the plain to ancient versions of the current Yellowstone "hot spot."

The Snake River Plain from Howard Mtn. near Pocatello, Idaho
American Falls Reservoir in the misty distance
Copyright Ralph Maughan

The north side of the Plain is where the basalt, covered by grass and sagebrush, "washed up" against the foothills of the Pioneer Mountains.

Basalt washed up against the foothills of the Pioneer Mtns. on the northern edge of the Snake River Plain
The northern edge of the Snake River Plain where
relatively fresh basalt "washed" up to the foothills of
the Pioneer Mountains (in the background). 5/97

Since the photo was taken, the area in the photo has
been to Craters of the Moon National Monument.
© Ralph Maughan

Revised last on March 7, 2004