The warmest , driest forested areas occur on south @-@ facing slopes from 3 @,@ 000 feet ( 910 m ) to 6 @,@ 500 feet ( 2 @,@ 000 m ) . Due to the occurrence of frequent non @-@ lethal fires , ponderosa pine dominate these forests alongside Douglas fir . The understory consist of bluebunch wheatgrass , Idaho fescue , mountain snowberry , and bitterbrush in drier areas and elk sedge , pinegrass , white spirea , mallow ninebark , and common snowberry at higher elevations .