additional permanent sources of stockwater, on the area. 

 Nearly all of the reservoirs were small (< 1 ha) and more than 

 one-third were dry by late summer in average water years . 

 During the driest years only 28 contained water, mostly in 

 small amounts and of low quality. Three of the 4 wells were 

 developed during the last 2 years of the study to supply 

 watering tanks at various sites on the south-central portion 

 of the area. During years or periods of above-average 

 precipitation, water is also available in natural depressions 

 throughout the area . 



Access is provided by a paved highway (U.S. 191) along 

 the western boundary, several unpaved "roads" extending 

 through the area from the highway, and numerous vehicle 

 "trails" along ridgetops. All unpaved roads and trails are 

 impassable when wet. 



Climate 



The climate is semiarid, characterized by moderately low 

 and variable precipitation, low relative humidity, moderate to 

 strong winds, and great extremes in temperature. 



Records for the U.S. Department of Commerce weather 

 station, Roy 8 NE, located approximately 25 km southwest of 

 the center of the study area show a 42-year (1943-1985) mean 

 annual temperature of 6.5 C (range 4.3 - 8.3 C, CV = 4%). 

 January is the coldest month (Fig. 3.5), with an average 

 temperature of -8.4 C, while July is the warmest (20.8 C) . 

 Mean annual (1939-1985) precipitation is 35.4 cm (range 17.9 

 - 63.9 cm, CV= 27%), most of which occurs as rain during 

 spring and summer (Fig. 3.5). Precipitation is normally 

 highest during June (7.5 cm) and lowest during February (1.0 

 cm). Total snowfall ranged from 0.2 m to 2.2 m. Snow depths 

 exceeding 0.3m are rare, though occasionally accumulations up 

 to 0.9 m persist for significant periods of time (e.g. 1977-78 

 and 1978-79). Warm, southwesterly "chinook" winds occur 

 periodically during many winters to moderate temperatures and 

 reduce snow accumulations. The average frost-free season is 

 128 days, but the effective growing season is shorter, usually 

 extending only from mid-April through the end of June. 



Trends in annual temperature, growing season and annual 

 precipitation, and winter snowfall and severity (Figs. 3.6 and 

 3.7) illustrate the marked seasonal, annual, and periodic 

 fluctuations that characterize the climate and weather 

 conditions on the area. Long-term (1580-1980) trends in 

 moisture were calculated as a relative moisture index from 

 tree-ring data for Douglas fir (Pseudotsuga menziesii) on the 

 study area by the University of Arizona Tree Ring Laboratory 

 (D. Meko and C. Stockton, pers . commun., Fig. 3.8). These 



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