22 BULLETIN 211, U. S. DEPARTMENT OF AGRICULTURE. 



lower levels into which the arroyos debouch, with a few that have come 

 in from the adjacent mesas or ridges. 



The physical factors that determine this distribution relate in some 

 way to local water and air drainage. While the upper courses of 

 such arroyos are likely to be deep and full of plants, the lower reaches 

 are usually dry, broad, flat, gravelly channels, at most but a few feet 

 lower than the surrounding land and practically bare of vegetation 

 or occasionally having a crop of range weeds. 



Woodlands. — As used here, the term woodlands refers to those areas 

 that are covered with a more or less scattering growth of low trees, 

 a plant formation occupying a zone between the grass-covered plains 

 and the forest-covered areas of the higher mountains. Typical wood- 

 lands occur on the lower parts of the mountains, ranging upward 

 from 1,000 to 2,000 feet above the level of the surrounding plains. 

 Where these plains are relatively low, as they are in the southern part 

 of the State, the wooded areas begin at about 5,000 feet elevation, 

 while farther north, where the plains are much higher, the lower limit 

 of woodland 'is sometimes as high as 7,000 feet. Throughout the 

 State the area is characterized by the presence in greater or less 

 abundance of low scrubby trees and numerous shrubs. Among these 

 occur various bunch grasses and numerous herbs during the growing 

 season. This plant formation often covers the lower drier ridges and 

 mountains to the summits, especially on the southern exposures 

 where the zone is nearly always broad, while on the higher mountains 

 and especially on steep northern slopes the zone is apt to be narrow 

 or sometimes almost absent. 



Forests. — Above the woodland zone in the mountains come the 

 forests. First, as one goes upward, are the open forests of western 

 yellow pine with interspersed parks (the transition zone), then the 

 denser forests of pine and Douglas spruce (mainly the Canadian zone) , 

 and last the dense spruce forests (Hudsonian zone), reaching the 

 timber line. These forests exist only because of the rainfall that 

 occurs at these levels, and the growing conditions thus produced 

 result in an abundant and varied flora, most of which is readily eaten 

 by stock. As the elevation increases, the forests become denser, 

 darker, and wetter. The growing season also is shortened, as is the 

 grazing season, the area above the transition zone being mostly 

 summer pasture. 



Above the timber line there are some ridges and peaks which have 

 a short-lived crop of grass, sedges, herbs, and a few low shrubs, but 

 this area is very rarely reached by stock even in the warmest of the 

 summer weather. 



Practically all of the lands held by the Federal Government lying 

 in the woodland zone and those above it are now administered as 

 national forest. 



