The most common vegetation type in the Intermountain West can be called sagebrush steppe, sagebrush grassland, shrubland, cold desert shrub, or simply western rangeland. Although there are differences in these terms and in the vegetation communities they describe, the common component among them is the presence of shrubs. A particular shrub called sagebrush dominates many of these communities, and occurs in combination with complex mixtures of other shrubs, grasses, and forbs. Climate, soil conditions, parent material and topography determine the general distribution of sagebrush and the various characteristics of shrubland communities. The dominant species of sagebrush at Craters of the Moon is mountain big sagebrush.
Mountain big sagebrush is widespread throughout the monument and is found in combination with the following types of grasses: bluebunch wheatgrass, Sandberg bluegrass, needle grasses, Idaho fescue, and cheatgrass. The four other species of sagebrush found at Craters are basin big sagebrush, three-tip sagebrush, early low sagebrush, and low sagebrush. Other common shrubs at Craters are antelope bitterbrush and rubber rabbitbrush. These two species are especially common on cinder cones. Sagebrush becomes a common vegetation component in areas with older substrates (geology) and where adequate soils have developed.
The sagebrush steppe ecosystem provides an important watershed and valuable habitat for wildlife at the monument, including sage grouse, mule deer, pronghorn antelope, songbirds, and small mammals. Management protection afforded by the area's wilderness status, along with the natural protection the surrounding barren lava flows provide, help keep many of the monument's plant communities in pristine condition.