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<br />(c' Large volumes of existing material regarding irrigation water,
<br />;.'" drainage, and phreatophytes have been reviewed and were rrost
<br />~;.,'"' useful in the preparation of this report.
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<br />GENERAL DESCRIPI'ION OF AREA
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<br />The area studied contains about five million acres. Generally,
<br />it includes all the land in Colorado which drains into the Rio
<br />Grande River. It is located in south central Colorado and in-
<br />cludes all or part of saguache, Rio Grande, Alamosa, Conejos,
<br />costilla, San Juan, Hinsdale, Mineral and Archuleta ColIDties.
<br />The area is wi thin the bolIDdaries of the proposed San Luis Valley
<br />Resource ConseIVation and Development project. The area is bolIDded
<br />on the west and north by the Continental Divide, on the east by
<br />the Sangre de cristo Range, and on the south by the Colorado-New
<br />Mexico state line. The Valley flcor is nearly flat, sloping from
<br />about 4 to 10 feet to the mile. The northem part of the Valley
<br />lies within a closed basin with no surface drainage outlet. This
<br />basin is separated fran the Rio Grande drainage by a 1= lying
<br />ridge several miles wide.
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<br />Over half the land in the study area is Federally =ed - national
<br />forests, public dcrrain, wildlife refuges - and includes the Great
<br />Sand Dunes National Monument.
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<br />Of the roughly 2-1/2 million acres of private or local government
<br />land in the area, about 20 percent is i=igated cropland, 10 percent
<br />pennanent pasture or hay, 20 percent woodland, and 50 percent range-
<br />land. (Refer to Map-l, Land Use.)
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<br />The frost-free season in the Valley ranges fran about 90 to 115
<br />days. precipitation averages about seven inches a year. Hail
<br />stonns are eamon, and strong winds may bl= from the souttMest
<br />in the spring and early surrmer.
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<br />Generally, soils of the Valley are coarse textured next to the
<br />rrountains and are a little finer textured ta.vard the center of
<br />the valley. They are underlain rrostly with sand or gravel at
<br />depths of one to four feet. During good water years, appreciable
<br />acreage along the west side of the Valley is cx:xrpletely or
<br />partially sub-irrigated. (Refer to Map-B, Soil and Water Table.)
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<br />Main irrigated crops are alfalfa, potatoes, barley, oats, grass,
<br />hay, and pasture. Native hay or pasture on high water table areas
<br />are an inportant part of many farms and ranches. Crop yields are
<br />high and quality of adapted crops lIDusually good. There are about
<br />46B,000 acres of i=igated cropland in the Valley and 212,000 acres
<br />of irrigated or sub-irrigated pasture and rreada.v.
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