ASPEN IN THE CENTRAL ROCKY MOUNTAIN REGION 
as 12,000 feet (Engelmann spruce timber line), in central Utah to 
extreme ranges of 10,500 feet, while in Idaho (Targhee National 
Forest region) it is seldom found above 7,500 feet. At these extreme 
altitudes snow may lie on the ground from the latter part of Sep- 
tember until the middle of June, and drifts are known to last well into 
August, so that the extension of the aspen may be limited by large 
snowdrifts where the local topography favors their formation. On 
south slopes at high elevations aspen becomes brushy, bent and 
Fig. 3. — Development of aspen root suckers. This shows how shallow suckering roots 
lie and how the suckers tend to develop closely around the highest point on the root 
twisted by heavy snows, or is confined at such elevations to moist 
areas only. 
The lower limits of the aspen type are found along streams far 
below the range of the extensive stands. In the western yellow pine 
type considerable areas of poorly developed aspen are common on 
north slopes and in moist swales, although the region may be devoid 
of permanent watercourses. Rarely, except in the Nevada region, 
do they enter the pinon- juniper type even along streams. In central 
Utah, where the western yellow pine type is lacking, aspen runs 
down to join the chaparral (oak and sagebrush types) at an eleva- 
