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

Abstract

Two seismic cross sections were run with a refraction seismograph near Spokane,, Wash,., in Hay and June l?5l» One section trended northsouth 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 1,000 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 1,600 to 1,700 feet in the State* boundary district and at 1,700 feet in the Hillyard Trough district.

Compilation of geologic, hydrologic, and ground-water flow modeling information for the Spokane Valley-Rathdrum Prairie aquifer, Spokane County, Washington, and Bonner and Kootenai Counties, Idaho

“…Late Tertiary landscape likely was characterized by the ancient Spokane−Rathdrum River following a course similar to today's Spokane River except in north Spokane where the river's course probably followed the Hillyard Trough on the east side of the basalt plateau of Fivemile Prairie (Newcomb and others, 1953). The river then flowed west along the present reach of the Little Spokane River valley toward the present main valley near Long Lake.…”

“…Weigle and Mundorff (1952) compiled well records and water-level and water-quality data for wells in the Washington part of the aquifer. Newcomb and others (1953) provided the first thickness information for the aquifer with the results of his seismic refraction profiles done near the Washington−Idaho state line and in the Hillyard Trough.…”

“…Numerous geophysical investigations have been conducted to determine the configuration of the base of the SVRP aquifer using several surface geophysical methods to investigate the subsurface characteristics of deposits and bedrock, including seismic refraction (Newcomb and others, 1953, Tanaka, 1975, Dion and Sumioka, 1991, HartCrowser, 2003, seismic reflection (SeisPulse Development Corporation and others, 1993;Gerstel and Palmer, 1994;Palmer and Gerstel, 1994;Palmer and others, 1995a, b;CH2M HILL, 1998, 2000aand S. Palmer, Washington Department of Natural Resources, written commun., 2005), and gravity (Purves, 1969;Hammond, 1974;and Adema, 1999).…”

Hydrogeologic Framework and Ground-Water Budget of the Spokane Valley-Rathdrum Prairie Aquifer, Spokane County, Washington, and Bonner and Kootenai Counties, Idaho

“…[Modified from http://pubs.usgs.gov/gip/geotime/divisions.html and http://www.geosociety.org/science/timescale/timescl.htm, accessed March 22, 2007. Abbreviations: ya, years ago; mya, million years ago; -, indicates a gap in the geologic record resulting from erosion and (or) The late Tertiary landscape likely was characterized by the ancestral Spokane River, which followed a course similar to that of today's Spokane River except in north Spokane where the ancestral river's course probably was through the Hillyard Trough on the east side of the basalt plateau of Five Mile Prairie (Newcomb and others, 1953). The river then flowed west along the present reach of the Little Spokane River Valley toward the present main valley near Long Lake.…”

Clay deposits of Spokane County, Washington

“…In the Spokane River valley, the Latah Formation lies· 21 unconformably on basalt and prebasalt granitic and gneissic rocks. Seismic profiles across the Spokane River valley indicate that the formation is more than 500 feet thick in places (Newcomb and others, 1953); Pardee and Bryan (1926, p. 8) stated that the Latah Formation is as much as 1,400-1,500 feet thick. In the area south of Mica Peak, beds of the Latah Formation are interbedded with the basalt flows and are less than 100 feet thick.…”