The High Lava Plains ecoregion is a vast, nearly level to undulating sagebrush steppe containing scattered volcanic cones and buttes. Elevation varies from 4,200 to 6,800 feet (1,280 to 2,073 m). The region is similar to the Dissected High Lava Plateau in its physiography, climate, and vegetation, but, unlike the plateau, it is internally drained. As a result, it lacks anadromous fish runs. It also differs from the plateau in having numerous intermittent lakes on the impermeable volcanic bedrock. Vegetation on the steppe includes Wyoming big sagebrush, low sagebrush, mountain big sagebrush, Lahontan sagebrush, bluebunch wheatgrass, Sandberg's bluegrass, Thurber's needlegrass, bottlebrush squirreltail, and Idaho fescue. Silver sagebrush, creeping wildrye, and mat muhly are found in depressions. Shallow and rocky soils support scattered western juniper. The federally threatened Warner sucker fish lives in permanent, shallow, weedy lakes and spawns in Nevada's Twelvemile Creek. The Wall Canyon area supports a unique fish species, the Wall Canyon sucker. Higher elevations once supported Lahontan cutthroat trout but water availability limits their present distribution. The largest of the Northern Basin and Range subregions, the High Lava Plains covers in Oregon and in Nevada, featuring a variety of land uses, including rangeland, wildlife habitat, irrigated pastureland and cropland, historic gold and silver mines, and active opal mines and clay quarries. It contains the Sheldon National Wildlife Refuge and lower elevations in the Hart Mountain National Antelope Refuge. Contiguous areas in California have not been mapped yet.