Exposed as hills uplifted and basaltic lava eroded away
Much of the region formed by wind and water erosion. Covered by a thick layer of rich topsoil of eroded volcanic material mixed with clay-like glacial sediment blown in from Puget Sound (loess). This makes up the Palouse Hills.
Irrigation not needed because of clayey glacial loess
The grasslands originally covering much of the region have now been generally replaced by domesticated grasses (wheat, oats, barley) and legumes (alfalfa, peas, lentils) Crop rotation and fallow fields help offset the loss of nutrients and water