Columbia Basin

Snake-Columbia Shrub-Steppe, Part IV, Columbia Basin
Floods of lava, floods of the Ice Age, and dry waterfalls
There are several distinct areas of this shrub-steppe ecoregion of the Columbia Plateau (NA 1309). For the purposes of this discussion, the ecoregion is subdivided into four sections, based on biological or geographic criteria.
The fourth area, the Columbia Basin, is the desert along the Columbia River in northern Oregon and central Washington. It is underlain by volcanic Columbia River basalts, but the area is most notable for the Ice Age floods that ranged from one million years ago to 13,000 years ago. In the Rocky Mountains to the east, ice dams formed and failed many times, releasing walls of water that surged southwest and flooded the area several hundred feet deep. The rocky barren lands created by the scouring of the floodwaters are known today as scablands (Montgomery 2012). Today there are geologic features throughout the Columbia River portion of the Snake-Columbia shrub-steppe that provide evidence of these floods. The floods were apparently carrying icebergs, since glacial erratics are scattered around places where the water was temporarily constricted. Wallula Gap (1) National Natural Landmark (NNL) is a two-km-wide constriction in the Columbia River, behind which water backed up during the catastrophic Lake Missoula floods 15,000 to 20,000 years ago, creating temporary Lake Lewis until the water drained, probably a week or so. Twice as much water backed up behind Wallula Gap as could pass through. Tributary rivers such as the Yakima and Walla Walla reversed flow as water surged up them. The Yakima River near Benton City has reverse flow badlands where there were extra scouring and potholes at a restriction to water heading the reverse direction. It is believed that Lake Missoula drained dozens of times, creating temporary floods and a temporary lake each time.
The Columbia River basalts are a remnant of an earlier event, the eruption of basalts on the edge of the North American continent. Typically, basalts are formed in the oceans at the locations where plates are spreading apart. However, there are also eruptions in the continental crust in a few places, forming major continental basalt plateaus. The 200,000-square kilometer area of Washington, Oregon, and Idaho along the Columbia and Snake Rivers is one such area. The eruption of basalts formed the Columbia Plateau between 17 million and 6 million years ago. The source of the eruptions was the present-day junction of Washington, Oregon, and Idaho, from which lava flowed and filled the area to the north and west, from Spokane to the Cascades and down the Columbia River to Portland. One flow, known as the Roza flow, moved 300 km in a matter of days from eastern Washington to the Dalles area. According to Hooper (1982), a lava front about 30 m high, over 100 km wide, and at a temperature of 1100˚C, advanced at a rate of five km per hour. One of the outcomes of catastrophic events like this was the preservation of sites like the Gingko Petrified Forest State Park (2), a NNL.
There is one National Historic Landmark in the Columbia Basin shrub-steppe. The B Reactor (3), Department of Energy, Washington (N46˚38’ W119˚39’), was the first production-scale nuclear reactor, built in 1943 to 1944, provided plutonium for the Trinity Test in New Mexico, the first nuclear detonation, and the “Fat Man,” the bomb dropped on Nagasaki. Following the demonstration of a chain reaction at the University of Chicago in 1942, the Manhattan Project began. A site at Hanford was chosen to construct a 250-MW reactor. The B Reactor is a National Historic Mechanical Engineering Landmark, National Civil Engineering Landmark, and Nuclear Historic Landmark.
The National Natural Landmarks of the Columbia Basin shrub-steppe tend to be related to the ice age floods; however, there is one commemorating a unique fossil deposit and another at a water gap of unusual relief.
Drumheller Channels (4), Columbia National Wildlife Refuge and Goose Lakes Unit of Columbia Wildlife Area, Washington (N46˚59’ W119˚12’) is an erosional landscape characterized by hundreds of isolated, steep-sided hills surrounded by braided channels. Between 8,000and 12,000 years ago, glacial Lake Missoula was periodically dammed by ice, then the ice dam broke dozens of times, creating massive floods that scoured the Columbia River drainage.
Grand Coulee (5), Washington is located between Grand Coulee Dam on the Columbia River and Soap Lake. This 50-mile-long ice age flood channel was carved by the periodic floods originating from Lake Missoula. Perhaps a highlight of the steep-sided channel is the dramatic Dry Falls (N47˚36’ W119˚21’), a 400-foot dry waterfall is 3.5 miles wide, now in Sun Lakes/Dry Falls State Park. Also occupying Grand Coulee upstream of Dry Falls is Banks Lake/Dry Falls Dam, a Bureau of Reclamation irrigation storage facility within the Columbia Project. Lower Grand Coulee is included in the Sun Lakes Unit of the Columbia Basin Wildlife Area.
Moses Coulee Great Gravel Bar (6), Grant County Public Utility District, Washington (N47˚17’ W120˚5’) was created during the first of the Lake Missoula floods, when the Columbia River surged down Moses Coulee. Later an ice lobe blocked this channel, and all later floods used Grand Coulee. Floods traversing Moses Coulee deposited a massive mile-wide, 400-foot deep gravel bar where it confluenced with the Columbia River. The terminus of the coulee is on Route 28 between Rock Island and Quincy. The gravel bar deposit can be viewed from across the river from Yo-Yo Rock Boat Launch of the Grant County Public Utility District on Wanapum Lake. Public access to the shoreline is available at the Apricot Orchard shoreline access site on Wanapum Lake on Route 28. The entirety of Moses Coulee and the Waterville Plateau to the north is an Important Bird Area (IBA) for greater sage grouse, sage sparrow, and sage thrasher.
Wallula Gap (1), Lake Wallula/ McNary Lock and Dam, Washington (N46˚3’ W118˚56’) is also an ice age flood site. During the Lake Missoula floods, this area on the Columbia River just south of the confluence with the Walla Walla River served as a large-scale hydraulic constriction. Because all the water could not overtop the ridge here, water backed up until the area could drain.
Ginkgo Petrified Forest State Park (2), Washington (N46˚57’ W120˚0’) is on I-90 at the Columbia River/Lake Wanapum crossing. This ancient fossil bed contains thousands of logs of Miocene age (15 million years ago) which were entombed in basalt lava flows. Ginkgo, redwood, Douglas-fir, and deciduous trees were growing in the forest. This is also an ice-age flood carved landscape; also present are occasional glacial erratics that rode on ice floes during the floods.
Umtanum Ridge Water Gap (7), Wenas Wildlife Area and BLM, Washington (N46˚48’ W120˚27’) is where the Yakima River goes through Umtanum Ridge. The Yakima River forms the eastern edge of the 105,000-acre Wenas Wildlife Area. Umtanum Ridge rises to 3,000 feet less than one mile from the Yakima River, where the elevation is 1,200 feet. On the north side of the ridge there are also cliffs along Untanum Creek, which has a hiking trail. This precipitous topography was formed as the Yakima River, which predated the ridge building, cut through the ridge as it was rising. To the north of Umtanum Ridge is Manastash Ridge, which has a similar water gap and topographic extremes. State Route 821 follows the river through Yakima River Canyon and the two water gaps between Ellensburg and Yakima. Between the two ridges is Umtanum Creek Valley, which is an IBA. The Roza Diversion Dam is located in the canyon at the water gap.