Level IV: (10e) Pleistocene Lake Basins
Pleistocene Lake Basins (10e)
The Pleistocene Lake Basins ecoregion is a nearly level to undulating lake plain that contained vast temporary Pleistocene lakes that were created by flood waters from glacial lakes Missoula and Columbia.
In Oregon, the flood waters accumulated from the eastern entrance of the Columbia River Gorge upstream to the Wallula Gap to form ancient Lake Condon.
Elevation varies from 300 to 1,200 feet (90 to 370 m).
Today, the region is the driest and warmest part of the Columbia Plateau, with mean annual precipitation varying from 7 to 10 inches (180 to 250 mm).
Major irrigation projects provide Columbia River water to the region, allowing the conversion of large areas into agriculture.
Where present, native vegetation consists of needle-and-thread, Indian ricegrass, bluebunch wheatgrass, Sandberg bluegrass, and basin big sagebrush. Alien cheatgrass covers broad areas.
The largest of the Columbia Plateau subregions, the Pleistocene Lake Basins covers 1,407 square miles (3,644 km2) in Eastern Oregon and larger areas in Washington, encompassing lower elevations throughout the Mid-Columbia Basin. It includes part of the Yakama Indian Reservation, as well as public lands within the Umatilla, Cold Springs, McNary, and Columbia national wildlife refuges, the Hanford Nuclear Site, and the Hanford Reach National Monument.[1][3]
Source: Wikipedia
