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The Cache la Poudre River basin has a continental type climate marked by wide ranges Df temperature and irregular precipitation. Westerly winds dominate the climate for most of the year; this allows the Rocky MDuntains to block atmospheric moisture originating from the Pacific Ocean. During the spring and early summer months, these westerly winds lose their predominance and moist air masses push up from the Gulf of Mexico. The plains portion Df the study area receives about 75 percent of its precipitation during April to September. . The mountainous region of the basin has a rigorous climate with long winters, heavy snowfall, and a short growing season. For example, average annual snowfall at Estes Park is about 96 inches compared to 43 inches at Fort Collins. Temperatures are more mDderate in the foot- hills than in either the mountains or the plains. Climatic characteris- tics of the plains are low humidity, warm summers, cold winters, light rainfall, and considerable year to year variations in precipitation. Climatic data for Greeley in the plains, Fort Collins in the foot- hills, and Estes Park in the mountains are presented in table 1. Eleva- tions for the three locations are 4648, 5025, and 7525 feet m.s.l" re- spectively. Precipitation in the mountains can be as much as 30 inches a year. Most of the mountainous pDrtion of the basin is forested and the greatest part of it is included within the Roosevelt National Forest. Forest occurs between elevations Df 6000 to 7000 feet m.s.l. up to about 11,000 feet m.s,l. Ponderosa pine or lodgepole pine, Douglas fir, and quaking aspen are found at the lower elevations. Spruce-fir fDrests are found at the higher elevations. Alpine grasses and brush and barren or snow-covered areas occur above the timberline. Most of the basin's rangelands and almost all of the arable lands lie in the plains. Range and dry cropland typify the northern part of the plains, while irrigated cropland occupies the southern part. 4 .