- Cowlitz County, Washington (data.census.gov)
Cowlitz County, Washington has 1,141.2 square miles of land area and is the 28th largest county in Washington by total area. Cowlitz County, Washington is bordered by Lewis County, Washington, Clark County, Washington, Columbia County, Oregon, Skamania County, Washington, and Wahkiakum County, Washington.
- Tukwila Formation—Andesitic to dacitic volcanic sandstone, siltstone, shale, tuff-breccia, tuff, volcanic mudflow (lahar), carbonaceous shales, and minor lava flows or sills. Typically massive; only local sedimentary interbeds indicate structure. K-Ar age on plagioclase from tuff-breccia at top of unit, about 3 km west of quadrangle, yielded an age of 42.0±2.4 Ma (Turner and others, 1983)