• The Columbia River Basalt Group is a large igneous province that lies across parts of the Western United States. It is found in the U.S. states of Washington, Oregon, Idaho, Nevada, and California. The Basalt group includes the Steen and Picture Gorge basalt formations. . In these ancient lake beds are found fossil leaf impressions, petrified wood, fossil insects, and bones of vertebrate animals.
Both flows are similar in both composition and age, and have been attributed to a common source, the Yellowstone hotspot. The ultimate cause of the volcanism is still up for debate, but the most widely accepted idea is that the mantle plume or upwelling (similar to that associated with present-day Hawaii) initiated the widespread and voluminous basaltic volcanism about 17 million years ago. As h
• Many of the rocks formed during the Cambrian, when the region lay at the edge of a continental landmass called Laurentia. These rocks include the Cambrian strata. As the Paleozoic Era progressed, several intensified geologic events occurred, including repeated episodes of faulting, and in turn, orogenies which involved upward lifting of a metamorphic core complex, creating mafic and rhyolitic dikes and stills.
• Extensive volcanism also occurred during the middle to late Cambrian, contributing further to the uplift of the area. This also contributed to a second round of block faulting, in which conglomerates, ash flows, and tuffs accumulated in the Snake Range.