Page 18 - The Geology and Ore Deposits of Sierra County, New Mexico - Bulletin 10

GENERAL FEATURES 17
the northern end of the county has an elevation of 4,420 feet. This great range in altitude and the abrupt topographic changes cause a wide variety of climatic conditions and types of vege- tation.
In the valley proper and on the plains and bolsons, the climate is warm and dry, and the average temperature is about 60° F. Extremes of cold are unknown, but for short periods during the summer months the temperature may be quite high. The average annual rainfall in this part 'of the country is about 10 inches, the greater precipitation occurring from July to Octo- ber. During this period violent thunder showers of short dura- tion frequently fill the arroyos and washes, and may prevent traffic on the highways for several hours at a time. Light snow- falls are of rare occurrence. In the spring and sometimes in the fall strong winds from the southwest carry an enormous burden of sand and dust, and are relatively important agents of scour and fill in the areas of alluvial deposits and along the river flood plains.
In the mountainous portions of the county considerably more rain and snow falls, and the average temperature is lower. The first snowfall may occur in November on the higher parts, and from then until April or May a blanket usually covers most of the high peaks and ridges.
The following table summarizes climatological data2 ob- tained at United States Weather Bureau stations in Sierra County.
In the flood plain of the Rio Grande, cottonwoods, willows and other similar small trees and shrubs abound. The slopes and plains bordering the valley bottoms support little vegetation other than greasewood, mesquite, and numerous varieties of cactus. On the bolsons and plains above the river, range grasses of various kinds grow in sufficient quantity to support a thriving cattle industry. In the foothills and on the lower mountain slopes, scrub oak and cedar appear, and the range grasses are abundant. The higher mountain slopes have excellent stands of
2 U. S. Dept. of Agriculture, Weather Bureau, Climatic Summary of the United States Sec. 29, Southern New Mexico, (To 1930, inclusive).