Surficial geology along the Spokane River, Washington and its relationship to the metal content of sediments (Idaho-Washington stateline to Latah Creek confluence): Geologic units

The Spokane River flows westward into eastern Washington out of the northern end of Lake Coeur d'Alene in northern Idaho. The river and lake lie downstream of the Coeur d'Alene mining district, where over 56 million metric tonnes of metal-enriched tailings were disposed into the Coeur d'Alene River between 1886 and 1968 (Long, 1998). Geochemical analyses of riverine sediments in the Spokane River by the Washington Dept of Ecology (Johnson, 1999), the US Geological Survey (Grosbois and others, 2001; Box and others, in prep.) and an EPA contractor (URS Greiner, 2000, 2001) have indicated that Spokane River sediments are variably enriched in metals derived from those tailings. In this report we present a surficial geologic map (plates 1 through 8) of the unconsolidated deposits within and along the Spokane River in eastern Washington between the Idaho stateline and the confluence with Latah Creek about 20 miles downstream. Existing sample datasets for sediments and soils in and along the Spokane River are also located on the map and the surficial geologic unit that was sampled is noted. This work was undertaken in cooperation with the Washington Department of Ecology and the Environmental Protection Agency.