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OOlH3 UPPER GUNNISON SUBBASIN '. Physical Description of Subbasin The Upper Gunnison Subbasin includes the drainage area of the Upper Gunnison River above the Gunnison Tunnel midway in Black Canyon. The eastern boundary is the Continental Divide and the western boundary the drainage divide between Cimarron Creek and the Uncompahgre River and between Mesa and Crystal Creeks. The elevation ranges from 7,500 to 13,000 feet. ,[g,ili Four of the major soil groupings are recognized in this subbasin: 2. Brown- Chestnut, 3. Mountain Prairie-Chestnut, 4. Gray Wooded-Brown Podzolic- Mountain Prairie, and 5. Alpine Meadow-Alpine Bog. These groupings are discussed in the general description of the Gunnison River Basin. The irrigated acreage in this subbasin is primarily located in soil groupings 2 and 3. Acreage of the great soil groups within these groupings and dis- tribution of this acreage by irrigated land and vegetative types is given in table 5. Land Use. Cover Conditions and Management The Upper Gunnison Subbasin has a total area of 2,529,684 acres, or 49 per- cent of the Gunnison Basin and contains approximately 72,000 acres of irrigated land, which represents 27 percent of the irrigated lands in the Basin. These irrigated lands vary in elevation from approximately 7,000 to 9,000 feet, and have a precipitation range froD about 10 inches to 20 inches annually. The frost-free season of about 70 days limits production to short-season crops. TIle majority of the irrigated land is used for the production of legume-grass hay. Very little alfalfa or clover is grown except as a minor percentage of the hay meadow composition. Grass hays are frost resistant and will grow over a longer time, thus having a favorable yield advantage. Nonirrigated lands represent 97 percent of the acreage within the subbasin. These lands are used primarily for watershed, recreation, range forage for both livestock and wildlife, timber production and other watershed purposes. Three percent of the subbasin lands are used for irrigated forage production. '. Irrigated lands within the subbasin generally have ample water supplies during the early part of the irrigation season, but are subject to shortages in the late season. Much of the irrigated land along the stream bottoms is flooded for weeks during the spring runoff period. Generally the unregu- lated irrigation water supply has restricted crops to low yielding sedge and wire-grass hay. High yields of good quality hay could be produced by land development and improved management of irrigation water. Other manage- ment practices such as drainage, application of fertilizer, seeding of fuproved hay mixtures and control of approximately 4,000 acres of phreatophytes would increase crop production in applicable areas. - 25 -