Extend from Mexico, north to Canada, and from the Black Hills, west to the eastern foothills of the Sierra Nevadas. Species are segregated along elevational gradients.

Subalpine (spruce-fir):

Engelmann spruce, sub-alpine fir; with mountain hemlock in Montana and northern Idaho; lodgepole pine and aspen are early-successional. At the highest elevation pines are most common (bristlecone, limber, and white bark pines), and alpine larch is found further north.

Montane:

Douglas-fir (upper elevations):
Douglas-fir is dominatnt, with white fir and blue spruce. In north, grand fir is west of the continental divide and white spruce east of the divide. Fire promtes lodgepole pine and aspen; some high elevation pine species are found on dry, exposed ridges.

Ponderosa Pine (lower elevations)
Ponderosa pine forms relatively open stands with a grass understory; lodgepole pine is early-successional; cottonwoods (western species), aspen and boxelder are found along streams.

Woodland Zone (pinyon-juniper):

An open forest of widely-spaced small trees (10-30'); forms the lowest conifer zone in the Rockies and represents the only conifer zone in much of the Great Basin. The zone includes several species of juniper and pinyon pine, and may extend from Mexico to Alberta (on the east side of Rockies the complex drops out in northern Colorado).

Black Hills:

A mixture of eastern and western species, including white spruce, paper birch, elm, hackberry, bur oak, ponderosa pine, and lodgepole pine.