Basalt flows in the vicinity of Pullman are approximately 2000 feet thick and rest on a granitic “basement” and sedimentary deposits. The individual flows are typically 50 to 100 feet thick. Almost all of this thickness is collectively termed the Grande Ronde formation of the CRBs. The Grande Ronde flows were emplaced over a period of 1 million years about 16 million years ago. A regional geology cross section through Pullman and Moscow (Bush and Garwood) from 2002-2005 Palouse Ground Water Basin Water Use Report, by Steve Robischon for the Palouse Basin Aquifer Committee, October 2006. Click here to enlarge.

Basalt flows in the vicinity of Pullman are approximately 2000 feet thick and rest on a granitic “basement” and sedimentary deposits. The individual flows are typically 50 to 100 feet thick. Almost all of this thickness is collectively termed the Grande Ronde formation of the CRBs. The Grande Ronde flows were emplaced over a period of 1 million years about 16 million years ago.

A regional geology cross section through Pullman and Moscow (Bush and Garwood) from 2002-2005 Palouse Ground Water Basin Water Use Report, by Steve Robischon for the Palouse Basin Aquifer Committee, October 2006. Click here to enlarge.

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