It contains dissected lava plains, rolling hills, alluvial fans, valleys, and scattered mountain ranges in the northern part of the Great Basin.

Its southern boundary is determined by the highest shoreline of Pleistocene Lake Bonneville, which once inundated the Central Basin and Range.

Dryland and irrigated cropland are found in some areas, but in general the soils are less suitable for agriculture than those in the Columbia Plateau and the Snake River Plain ecoregions.

Level IV mapping is not yet complete in California, and the information below includes only the sections in Oregon, Idaho, Nevada, and Utah.

Understory species are denser and biological soil crusts tend to be more extensive and in better condition than at similar elevations in the Central Basin and Range.

[1][2][3][4] The Semiarid Hills and Low Mountains ecoregion is higher and more rugged than the sagebrush plains and basins of neighboring regions.

The region is covered by mountain big sagebrush, low sagebrush, and associated grasses and understory plants, including bluebunch wheatgrass, Sandberg bluegrass, Great Basin wildrye, Indian ricegrass, cheatgrass, Idaho fescue, needle-and-thread grass, snowberry, and serviceberry.

The region includes streams that have been designated for protection as critical or high priority habitat for Yellowstone cutthroat trout and other fish.

Water quality has been lightly to moderately degraded by human activities, such as historic gold mining and livestock grazing, which is the primary land use today.

Some basin floor playas collect and evaporate water seasonally, but not as extensively as the High Desert Wetlands.

Sedges, rushes, black greasewood, tufted hairgrass, mat muhly, meadow barley, creeping wildrye, and Nevada bluegrass occur in wetter areas.

Although the region's climate and vegetation are similar to the Dissected High Lava Plateau, its lithology is more varied, stream density is higher, and water availability is greater.

[1][2] The High Lava Plains ecoregion is a vast, nearly level to undulating sagebrush steppe containing scattered volcanic cones and buttes.

The federally threatened Warner sucker fish lives in permanent, shallow, weedy lakes and spawns in Nevada's Twelvemile Creek.

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 10,262 square miles (26,578 km2) in Oregon and 5,740 square miles (14,867 km2) 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.

Potential natural vegetation is mostly saltbush-greasewood, featuring Nuttall sagebrush, squirreltail, shadscale, winterfat, and greasewood.

Less rugged than the surrounding hills and mountains, it is dominated by sagebrush grassland and lacks the woodlands, open conifer forests, and saltbush–greasewood vegetation of neighboring regions.

The steppe valleys are less suitable for cropland agriculture and have less available water than many parts of the Snake River Plain, but non-irrigated wheat and barley farming is common.

[2][4] The disjunct Semiarid Uplands ecoregion includes scattered hills, low mountains, volcanic cones, buttes, and rocky outcrops that rise out of the drier Dissected High Lava Plateau and High Lava Plains, as well as midelevation zones in the Hart, Steens, Owyhee, Jarbidge, and Santa Rosa mountains.

Finely textured soils support big sagebrush, low sagebrush, antelope bitterbrush, serviceberry, snowberry, mountain-mahogany, and associated grasses, such as Idaho fescue, bluebunch wheatgrass, Sandberg bluegrass, Nevada bluegrass, Great Basin wildrye, bottlebrush squirreltail, mountain brome, and Thurber needlegrass.

The density and extent of juniper varies over time and is dependent on long-term climate fluctuations, grazing pressure, and fire suppression.

These are partially glaciated, high, rugged mountains with glacial features including moraines, cirques, and tarn (lake)s. Perennial or intermittent, high gradient, cold streams are fed by snowmelt and springs, supporting federally threatened bull trout and Lahontan cutthroat trout in Nevada.

Alpine areas on Steens Mountain were seriously eroded following intense grazing by domestic sheep in the late 19th century.

Alluvial fans and hills support Wyoming big sagebrush, spiny hopsage, rabbitbrush, Thurber needlegrass, Indian ricegrass, Sandberg bluegrass, and bottlebrush squirreltail.

This region is mostly barren; vegetation, where present, is sparse and composed of very salt-tolerant plants, such as alkali sacaton and black greasewood.