Surprise Valley Chamber of Commerce
Where the Pavement Ends and the West Begins...

Geology of Surprise ValleyNew Icon

Surprise Valley and the Warner Mountains lie at the western edge of the Great Basin, an area drained by streams that flow into local skinks, rather than into river systems that flow into the sea. The corrugated, north-south topography of the Great Basin and Range province is the result of stretching and extension of the western part of the North American tectonic plate for 40 million years.

During the extension, the upper brittle part of the crust breaks along faults, resulting in alternating basins (valleys) and ranges (mountains). Sediments eroded by rain from the mountains ends up in the basins. In Surprise Valley the sediments are 7,000 feet deep. The gravely and sandy layers of the basin hold water for ranchers to grow feed crops. See the Geologic Field Trip Guide by Gail Mahood, Stanford University, 2006 and the other references below for more and sometimes overwhelming detail.

Surprise Valley Geology Details

The Warner Range to the west of Surprise Valley is a major west-tilted fault block bounded on its eastern side by the Surprise Valley normal fault system. The fault system separates the northeastern Basin and Range Province on the East, which has undergone 10-15% extension since the Miocene, from the Modoc plateau to the West, a relatively unextended region with a thick sequence of flat-lying Pliocene and younger volcanic rocks.

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Page modified: 01 Jul 2022 17:29:19 -0700