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UNITED STATES DEPARTMENT OF AGRICULTURE <br />Soil Conservation Service. Colorado <br />Technical Guide <br />Section II E <br />RANGE SITE N0. 289 ~ <br />Field Office <br />AUQUSL 1975 <br />RANGE SITE DESCRIPTION <br />for <br />CLAYEY FOOTHILLS <br />_ Land Resource Area: Central Desertic Basins, Mountains, <br />and Plateaus (34) <br />Colorado and Green Rivers Plateaus (35) <br />_ ~ - Southern Rocky Mountains (48) <br />A. PHYSICAL CHARACTEAf5T1C5 <br />1. Physiographic Features <br />This site occupies gently sloping to rolling benchlands, footslopes, <br />fans, valleys and broad ridges. It Is commonly associated with <br />~-.. shalom hills. Slopes are generally between 1 and 12$ and are not <br />significant ~o plant growth. Elevation is between 5500 and 7000 fcet. <br />2. Climatic Features • <br />Average annual precipitation is 12 to 16 inches, except for a few <br />small areas where it may reach 18 inches. Of this, 35 to 40$ falls <br />a., snow and 40 to 45$ falls between May 1 and September 30. Summer <br />moisture is mostly from thundershowers in late July, August and <br />September. A dry period from May to early July is typical, and June <br />is normally the driest month. Vide yearly and monthly deviations <br />are common. The most active growth of major native plants usually <br />starts iq_Aprll. It~~extends through most of June for some plants <br />.but ends in late May for others. Many plants can again take advent- <br />age of late Summer rains if to good vigor. <br />Hean annual temperatures are 45° [0 48° F, with a frost-free period <br />of 90 to 140 days. Annual range in temperature is from 90° to -15° <br />or -20° f, although higher and lower extremes are sometimes recorded. <br />The typical late spring and early summer dry spell puts warm-season <br />plants at a distinct disadvantage compared to plants that can start <br />earlier on stored winter moisture and spring rains. Deep storage <br />of winter moisture allows sagebrush and small trees to complete <br />strongly with shallower-rooted grasses during this dry period, espec- <br />ially if other factors encourage the spread of such plants. <br />r <br />• <br />