32 
The Colorado Experiment Station 
4. White fir zone. 8,500-10,000 feet. 
5. Engelmann spruce-balsam fir zone. 10,000-11,500 feet. 
6. Alpine zone. Above timber-line. 
SAN LUIS VALLEY 
1. Shrub-steppe, chiefly greasewood and rabbitbrush. 7,500- 
8,000 feet. 
2. Pinyon pine-juniper zone. 8,000-8,500 feet. 
3. Yellow pine-Douglas fir zone. 8,500 or 9,000-9,500 feet. 
4. Lodgepole pine zone. 9,500-10,000 or 10,500 feet. Lodge- 
pole pine is rare on the eastern side of the Valley. White fir may 
here take its place. 
5. Engelmann spruce-balsam fir zone. 10,000 or 10,500—tim¬ 
ber-line. 
6. Alpine zone. Above timber-line. 
SOUTHWESTERN AND MIDDLE-WESTERN COLORADO 
1. Shrub-steppe. Sagebrush. Best developed under 7,000 feet, 
but frequently running up to 9,500 feet in warm valleys. 
2. Pinyon pine-juniper zone. A belt of varying vertical 
width. 
3. Yellow pine-Douglas fir zone. 7,000 or 7,500-8,000 or 8,500 
feet. Douglas fir frequently goes much beyond the limits of yel¬ 
low pine. Aspens well developed. 
4. Engelmann spruce-balsam fir zone. Up to timber-line. 
5. Alpine zone. Above timber-line. 
NORTHWESTERN COLORADO 
1. Shrub-steppe. Sagebrush. Up to 6,000 or 7,000 feet. 
2. Chaparral, chiefly of oak and buckbrush. 6,000 or 7,000- 
8,000 feet. 
3. Lodgepole pine zone. 8,000-10,000 feet. Aspens abundant. 
4. Engelmann spruce-balsam fir zone. 10,000-11,500 feet. 
5. Alpine zone. Above timber-line. 
* 
In Middle and North Parks the zone immediately bordering 
on sagebrush is one of lodgepole pine and aspen. 
It must be understood that the width of these vegetation zones, 
as well as their vertical ranges and their composition, vary consid¬ 
erably over the state. Furthermore, the lines of demarcation are 
seldom sharp and abrupt, but the change from one zone to another 
is gradual and, over a considerable area, there is a mingling of the 
typical plants of each zone. 
Throughout the state, the pinyon pine-juniper and chaparral 
associations are usually intermediate between grassland or sage¬ 
brush and the timbered slopes. Yellow pine is always a tree of 
