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C.C. Cragin

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The C.C. Cragin Project was completed in 1964, and water storage began in 1965. C.C. Cragin Dam (formerly Blue Ridge Dam) was designed by the consulting firm of Leeds, Hill and Jewett, Inc. and was constructed by the Phelps Dodge Corporation. The Salt River Project (SRP) transferred ownership of C.C. Cragin Dam and other project features to Reclamation under a Warranty Deed signed on September 30, 2005. C.C. Cragin Dam is located in north central Arizona, in the Coconino National Forest, section 33, T14N, R11E, Gila and Salt River Baseline and Meridian. The structure impounds waters of East Clear Creek, a tributary of Clear Creek and the Little Colorado River. The dam is founded in the geologic unit known as the Coconino sandstone. The Coconino formation is capped by the Kaibab Limestone along a horizontal contact approximately 25 feet below the crest of the dam.

The dam is an unsymmetrical thin concrete arch approximately 170 feet high, and with a crest length of 492 feet. The arch varies in thickness from 6 feet at the crest to 14 feet at the base. The arch is seated at its base upon a base block with a “slip plane” consisting of two graphite impregnated asbestos sheet, one bonded to the base block and the other to the arch. The outer sections of the arch rest upon hinge blocks cast on each abutment. The hinge block seats are in the form of a circular socket to provide rocker action. These seats are corrugated transversely for shear resistance. Gravity thrust blocks or buttresses in contact with the arch are provided at the upper end of each hinge block and abutment.

Geology - C. C. Cragin Dam (formerly Blue Ridge Dam and Reservoir) is located on the Mogollon Rim of northern Arizona approximately 23 miles north-northeast of Payson, Arizona. The Mogollon Rim is a 2,000- to 3,000-foot high escarpment that angles diagonally for about 200 miles across north-central Arizona. It marks the boundary of the Colorado Plateau with the Arizona Transition Zone to the southwest. The surface of the Colorado Plateau is composed of sedimentary rocks, primarily rocks of Permian age.

At the dam site, East Clear Creek has incised a gorge through the Mogollon Rim and the Permian Kaibab Limestone and into the underlying Coconino Sandstone. At the dam site, the Kaibab is composed of moderately hard to hard limestone with occasional interbeds of sandstone and occasional chert. Fractures in the Kaibab are widely spaced, and are occasionally weathered to depths of several meters. The contact between the Kaibab and the underlying Coconino Sandstone forms a prominent erosional notch, visible downstream of the left abutment. Most of the dam, including the base block, hinge blocks, both thrust blocks, and the base of the gravity wall are founded in jointed Coconino Sandstone. The Coconino Sandstone is quartzose, moderately hard, moderately to well cemented, lithified, fine grained eolian sand deposit which exhibits strongly developed cross bedding and variable porosity. The Coconino Sandstone is slightly altered by weathering at the surface and is cut by widely spaced vertical and horizontal fractures. The Coconino Sandstone is also exposed in the spillway channel below the left abutment of the dam.

Last updated: Sep 09, 2014