Another view of this rough terrain about 50 miles from my home. (80k)
"Washington State is an exceedingly complex place geologically, but for purposes of understanding the Scablands, it is very simple. There are only two units to consider: resting atop crystalline basement are the Miocene Columbia Plateau flood basalts, about 15 million years old. On top of the basalt is loess. The loess (wind-blown sllt) was derived from glacial outwash eroded out of the Cascade Range and blown eastward. In eastern Washington are the thickest loess deposits in the United States, up to 100 meters deep. The Scabland channels are cut almost entirely in loess and basalt." Steve Dutch, Professor.