Seismic cross sections across the Spokane River valley and the Hillyard Trough, Idaho and Washington

Two seismic cross sections were run with a refraction seismograph near Spokane, Wash., in Hay and June 1951. One section trended north-south across the Spokane River valley plain Just east of the Idaho-Washington boundary; the other trended east-west across the strath just north of the Hillyard section of Spokane.

Each section secured data that permitted the compilation of a graphic cross section showing the position of (1) the water table, (2) the base of the glacial and glaciofluviatile deposits, and (3) the generalized base of the Latah formation and associated deposits (which is the top of the consolidated bedrock).

The data confirm the inference of Pardee and Bryan that the granitic bedrock lies at an altitude of about 1,0OO feet beneath the valley plain near the State boundary. The base (a heretofore unlocated feature) of the glacial outwash deposits, the main aquifer of the area, was determined as an uneven plane at an altitude of 1,800 to 1,700 feet in the State-boundary district and at 1,700 feet in the Hillyard Trough district.