Land Utilization in the Scablands of Eastern Washington

Abstract

D TV ECIDED contrasts in land utilization occur on the Columbia Plateau in eastern Washington between the Palouse and the channeled Scablands that interlace in a mystifying manner across the plateau. The area discussed lies within the Big Bend of the Columbia River east to Idaho, south of the Spokane River and north of the Snake River. The bedrock consists of thick basaltic lava flows with a few island hills of crystalline rock, called steptoes by Russell in his Geology and Water Resources of Nez Perce after Steptoe Butte, rising above the lava. Lake beds, called the Ellensburg formation, were deposited on the surface of the lava plateau in the western part of the Columbia Basin. Both the basalt and the lake beds are pervious, and surface streams are, therefore, relatively scarce. A mature topography was developed by the Pleistocene period on the plateau in Washington. Little residual soil was formed from the bedrock. The surface soil was largely of loessial origin and had been heaped into hills, elongated southwest to northeast, by the wind, according to J. Harlen Bretz. During the glacial period a tremendous flood that resulted from the very rapid melting of an ice sheet, poured down across the plateau, which slopes towards the confluence of the Snake and Columbia rivers. This flood devastated the country. It was in places hundreds of feet deep. Divides were overtopped, and vast anastomosing streams washed away the surface soil in their beds and, by plucking out the basalt, excavated numerous deep basins, many of which now form lakes. The bare basalt is locally called scabrock. The intermingled channels formed by flood erosion are called Large bars were deposited by the flood, and the Quincy Basin, in southern Grant County, was largely buried under sand and gravel. The area of the scablands is about 2,800 square miles, with 900 square miles additional buried in debris left by the flood. Figure 1 illustrates the anastomosed character of the scablands. The scablands include numerous smaller channels within the main canyons, pits, buttes, elongated lake basins, mesas, steep cliffs, dry waterfalls, hanging valleys, islands of the original less covered mature relief, isolated columns, and other erosional forms. The erosional and depositional forms are wholly the work of running water. The giant streams are extinct, but the evidence of the flood remains. Before the flood the area was covered with deep, fertile less; after the flood the lower land affected by the catastrophe was barren scabrock, pitted by numerous basins containing ponds and lakes, and covered by debris in many places forming bars and other deposits. Since the epochal formation of the