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Background



The San Juan River sub-basin is the second largest of the three sub-basins that comprise the Upper Colorado River Basin. It drains about 38,000 square miles of southwestern Colorado, northeastern Arizona, northwestern New Mexico, and southeastern Utah. From its origins in the San Juan Mountains of Colorado, the San Juan River flows approximately 31 miles to the New Mexico border, 190 miles westward to the Four Corners area, and another 136 miles to Lake Powell. In its upper reaches, the river traverses rugged terrain and has a relatively high gradient. The river emerges from canyon-bound reaches shortly after entering New Mexico and flows through a broad floodplain for much of its course in New Mexico and Utah. About 70 miles upstream of Lake Powell, the river again enters canyon reaches for the remainder of its course. The river is generally restricted to a single channel in canyon portions, but is often divided into several channels in floodplain reaches.

In 1922, the seven basin states of Utah, Colorado, Wyoming, New Mexico, Arizona, Nevada, and California signed a compact dividing the Colorado River between the Upper and the Lower Colorado River basins. In 1948, the Upper Basin states (Wyoming, Colorado, Utah, and New Mexico), together with Arizona, signed an agreement apportioning the upper basin share between the states. Each of the States and the Bureau of Reclamation under the authority of the Colorado River Storage Project (CRSP) Act , initiated the development of the waters of the Upper Colorado River basin. The passage of the CRSP Act allowed for the construction of many large mainstem impoundments on the Colorado River and various tributaries including Navajo Dam on the San Juan, Flaming Gorge on the Green River, and the Aspinall Unit on the Gunnison River.

While the construction of these impoundments was essential for the development of water storage and flood control and to allow the Upper Basin States to develop their water resources, their construction and operation altered natural river ecosystems and, thereby, the native floral and faunal communities of the Colorado River. As a result, natural riverine habitats were altered, migration routes were blocked, and selective chemical treatments were applied to eradicate native species in favor of nonnative sport fish species.

 

This webpage was last modified on: September 10, 2007

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