Glaciation has left broad flat valleys between mountain ranges.
Elevation determines the dominant vegetation.
Highest areas are alpine tundra. The subalpine zone is dominated by Engelmann spruce and subalpine fir, with ponderosa pine and Douglas fir in the montane zone below that. Stand-replacement fire can change forests in either of those zones to lodgepole pine or aspen. Grass and sagebrush occur under open pine forests that grade downslope into grasslands, woodlands, or shrubsteppe. Riparian Calliope Hummingbird Highest percent population of any physiographic area.