BREEDING-GROUNDS OF C. SPRETUS. 
71 
directly northward to the 43d parallel of latitude ; here it bends north- 
west, reaching about the 113th meridian, where it crosses the northern 
boundary of the United States, varying in height from 8,000 to 12,000 feet 
above sea level, with peaks here and there shooting up to 14,000 feet. 
The heaviest mountain masses are found in Colorado and Northwestern 
Wyoming, the former being interrupted by elevated basins or parks 
eight to ten thousand feet above sea level ; the latter by valleys extend- 
ing north and south. Passing westward from this eastern mountain wall 
(for such it really is), in Colorado and Wyoming, we traverse a broad, 
barren plain, with Artemisia as its characteristic plant, until we reach 
the Wasatch range or western wall, in Utah. This broad area, which 
averages in elevation about 6,000 feet, is here and there broken into 
rolling hills with occasional ridges, and is almost entirely free from 
forests. Passing to the west side of the Wasatch, in Utah, we enter 
the great Salt Lake basin, which is also mostly barren, with scanty 
vegetation, and is interrupted by numerous narrow ridges running north 
and south. It has an average elevation of about 4,000 feet. Passing 
west of the Teton range, from Wyoming into Idaho, we enter upon the 
broad, level, and comparatively barren valley of Snake Eiver, which is 
also without forests. The portion of Montana west of the first range is 
rugged, being broken into a series of ridges and valleys running north 
and south, more or less clothed with coniferous forests. The chief tim- 
ber areas in this extensive region are found upon the mountain masses 
in Colorado and Northwestern Wyoming and in the western part of 
Montana. 
The main or eastern range, as heretore stated, is flanked on the east 
by a broad and treeless plain extending from its base eastward to the 
Missouri Eiver. That portion of this plain where it leaves the mountains 
in Colorado and Wyoming has generally an elevation of from 5,000 to 
6,000 feet and slopes eastward at a rate varying from 6 to 15 feet per 
mile. As we proceed northward along the mountain flank from the 
Black Hills, the elevation grows less and less, so that the great barren 
plateau of Central Montana ranges from 2,000 to 3,000 feet above sea 
level. 
The term "barren-' as here used is not to be taken in the sense of 
desert, but as implying without arboreal vegetation, and as usually 
clothed with a moderate growth of grass, sage, and other plants of a 
similar nature adapted to a dry climate, and generally suited for pas- 
turage. The forests, wherever found, consist almost entirely of pine 
and fir, and are confined almost entirely to the mountain ranges where 
the snow is most abundant. 
There is no part of this district where agricultural operations can be 
carried on without irrigation, as the rainfall seldom exceeds, in any 
portion, 20 inches in a year, and in many parts does not average more 
than 6 or 7. The air is very dry, the relative humidity sometimes fall- 
