Clastic Dikes Intruding Columbia River Basalt
Clastic dikes in the Columbia Basin are wedge-shaped bodies composed of silt, sand and gravel. The character of the dike-filling sediment at any given location is governed by what surficial material was present when glacial outburst floods swept across the landscape. There are hundreds of thousands of these features to be found throughout this vast region. The dikes cut various sedimentary units, including the Ringold, Snipes Mountain, and Ellensburg/Latah Formations. Dikes also penetrate sediments of the Dalles Group, nodular caliche/loess/calcrete layers in the Palouse Loess, "pre-Late Wisconsin" flood-related deposits, the Touchet Fm, hillslope and debris flow deposits with stage I-II caliche horizons, and the Clearwater Gravels. In several locations, the dikes, originating in the Touchet Beds, descend into the Miocene Columbia River Basalt bedrock.