Most of the region has been glaciated. In the several Rocky Mountain trenches, there are flat or nearly flat valleys, some of which are several miles wide. A stand of giant western redcedar in the Northern Rocky Mountain Province, Kootenai National Forest, Montana.
Summer days are often hot and nights cool.
Summers are usually dry, because westerly air masses draw the dry climate of the Pacific coast across the area. As a result, there is a distinct climatic gradient from north to south and east to west. Snowfall in winter is heavy, but permanent snowfields and glaciers cover only rather small areas. Well-marked life belts are a striking feature of the province. The subalpine belt is dominated in most places by Engelmann spruce and subalpine fir.