WSP07965

• File Number: 8446
• Description: Cache La Poudre Project
• State: CO
• Basin: South Platte
• Water Division: 1
• Date: 7/1/1983
• Title: Cache La Poudre Project Study and Related Correspondence
• Water Supply Pro - Doc Type: Report/Study

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There are a moderate number of furbearers in the area including badger,
beaver, marten, muskrat, skunk and long-tailed weasel. Varmints common to the
area are coyote, crow, ground squirrel, magpie, marmot, porcupine, red fox,
rock squirrel, raccoon, starling and prairie rattler.

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Amphibians found in the upper basin are salamanders, toads and frogs.
There are eleven species of reptiles, the most common of which are the rock
lizard, bull snakes, garter snakes and prairie rattlesnakes.

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In addition to the above, there are 29 species of non-game animals and 124
species of non-game birds. The Cache la Poudre Wild and scenic River Draft
Environmental Statement and Study Report lists two species on the Endangered
and Threatened species List: the Peregrine falcon and the greenback cutthroat
trout.

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GEOLOGICAL AND GEO'.rBCIIIIIlCAL CQ!iISIDERATIOIIS

1. Geological Setting

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The Cache la Poudre River Basin is located in the geomorphological
province known as the Front Range. The Front Range is an uplifted region
(horst) which lies adjacent to the down-dropped block (relative to the Front
Range) known as the Denver Basin graben.

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The upper basin is almost entirely contained within uplifted, very
old Precambrian crystalline rocks. These uplifted crystalline rocks form part
of the easternmost mountain range in Colorado, referred to as the Front
Range. Steeply dipping, younger Paleozoic and Mesozoic sedimentary rocks
flank the older crystalline rocks at the eastern edge of the Front Range. At
this crystalline-sedimentary contact, the topography changes from steep high
mountains to the flat Great Plains. Locally resistant sandstone and limestone
beds form hogbacks parallel to the eastern edge of the mountains. These
hogbacks give way to relatively flat lying sedimentary rocks that underlie the
Great Plains.

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2. SeiSllllcity

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The Front Range is generally recognized as a low seismic region. The
youngest faulting in the area is about 70 miles to the south along the Derby
Fault near Denver. The pumping of military arsenal wastes down disposal wells
in the middle to late 1960's had caused movements along the Derby Fault,
resulting in earthquakes with a maximum magnitude of 5.5 on the Richter
scale. In general, the study area is characterized by low seismic activity
with Richter magnitudes rarely exceeding 5.0.

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G. WATER SUPPLY

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The native water supply in the Cache la poudre River basin is supplied by
snowmelt from the perennial snow fields in the high mountains and, to a lesser
extent, from rainfall. The bulk of this runoff is from the headwaters of the
mainstem and South Fork in the high mountains within and bordering Rocky

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