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Last modified
3/26/2010 3:55:22 PM
Creation date
9/30/2006 10:21:06 PM
Metadata
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Publications
Year
1997
Title
Report on Ground Water Recharge and Mangement Project Rio Grande Basin, Colorado
CWCB Section
Finance
Author
Davis Engineering Service, Inc.
Description
Data for understanding mechanism of ground water recharge in the San Luis Valley & construct major recharge structure to facilitate ground water storage with winter surface diverersion
Publications - Doc Type
Tech Report
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<br />1 <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br /> <br />1.4 HYDOLOGEOLOGIC SETTING <br /> <br />The setting for this study is a high mountain valley called the San Luis Valley. The valley is <br /> <br /> <br />located along the Grande Rift which, from a geologic perspective, formed by tectonic movement <br /> <br /> <br />whereby the earth's crust pulled apart creating a north-south trench. The basement rock in this <br /> <br /> <br />trench is shallower on the west side of the valley where it is hinged and tipped downward toward <br /> <br /> <br />the east. On the east side of the valley near the Sangre de Cristo Mountains this basement rock <br /> <br /> <br />has dropped to depths of as much as 15,000 feet below present land surface. The downward <br /> <br /> <br />tilting of this basement rock easterly is not uniform. In the pulling apart process, a ridge <br /> <br /> <br />remained in the basement rock along a north-south direction near the center portion of the valley. <br /> <br />This ridge is referred to by geologists as the Alamosa horst. The deeper down faulted sections of <br /> <br /> <br />basement rock are called the Monte Vista graben and Baca graben. An east-west cross section of <br /> <br />the valley from a paper by Brister and Gries (1994) is included in Figure 1-2. Figure 1-3 shows <br /> <br /> <br />the location of the cross section in the valley. <br /> <br />As this trench expanded over tens of millions of years, it was filled by material eroded from the <br /> <br /> <br />nearby mountains encompassing the valley. Significant portions of the filled material that <br /> <br />accumulated in this trench entered from the San Juan Mountains while they were being built <br /> <br /> <br />through volcanic activity. Several fill beds extending across this valley trench from west to east <br /> <br /> <br />have been identified as volcanic flows. One of these flows, called ash-flow-tuffs, extend from the <br /> <br /> <br />surface on the western side of the valley and dips downward as it extends across the entire valley. <br /> <br />These ash-flow tuffs interbedded with sediments are found at depths of over 9,000 feet below <br /> <br /> <br />ground surface easterly of the Town of Hooper. <br /> <br />The top few thousand feet ofthe valley fill are rocks, gravels, sands and clays deposited by <br /> <br /> <br />erosion of the San Juan and Sangre de Cristo Mountains. Extensive erosion of these mountains <br /> <br /> <br />occurred as the ice age ended. As recently as 20,000 years ago, the high mountain valleys were <br /> <br /> <br />still partly clothed in glacier ice. Large stream and river flows out of the mountains carried the <br /> <br /> <br />sands and gravels found in the alluvial fans located around the edge of the valley and carried <br /> <br />1-4 <br />
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