Level IV: (80d) Pluvial Lake Basins
The Pluvial Lake Basins ecoregion contained vast lakes during the Pleistocene epoch that have now mostly disappeared. It is characterized by gently sloping, internally drained basins with lake terraces, playas, beach plains, stream terraces, intermittent lakes, fan skirts, and cool springs. Elevation varies from 4,200 to 6,200 feet (1,280 to 1,890 m). Some basin floor playas collect and evaporate water seasonally, but not as extensively as the High Desert Wetlands. Dry lake beds near the Cascade Mountains have a significant layer of volcanic ash.
Greasewood, inland saltgrass, and seepweed grow in alkaline soils. Better drained, less alkaline soils are dominated by Wyoming big sagebrush and basin big sagebrush, with rubber rabbitbrush, Great Basin wildrye, bottlebrush squirreltail, Indian ricegrass, Sandberg’s bluegrass, Thurber’s needlegrass, and cheatgrass.
The land is used for rangeland and sprinkler-irrigated alfalfa farming.
The region covers 2,092 square miles (5,418 km2) in Oregon and 342 square miles (886 km2) in Nevada.