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<br />
<br />o Juan River are th:e Navajo, Los Pinos, Animas,
<br />, and La Plata Rivers. The other main tributaries
<br />c.;.J in the basin are the Dirty Devil, Escalante,
<br />.J and Paria Rivers which drain a portion of the
<br />IM'I> eastern slope of tbe Wasatch Plateau in Utah.
<br />,...The reporting area includes about 38,600
<br />square miles in PPrtions of Utah, New Mexico,
<br />Arizona, and Colotado.
<br />The largest tow~s are 'Durango and Cortez in
<br />Colorado; Montice'llo and Blanding in Utah;
<br />,
<br />and Farmington inl New Mexico. Page, near
<br />Glen Canyon Dam,: is the only community of
<br />significant size in Arizona. Most of the re-
<br />maining Arizona pc\rtion is in the Navajo Indian
<br />Reservation. '
<br />Mining and agricJJ/ture form the economic
<br />base for the San JU,an-Colorado reporting
<br />area. The agricultu(al development is similar
<br />to that of the Uppet Main Stem with most of
<br />the cropland devote;ct to livestock feeds but
<br />with production of diversified market crops on
<br />lands with favorable: air drainage. The main
<br />market crops are frult, vegetables, and dry
<br />beans. Oil, natural gas, and coal are the
<br />most important min&rals produced. Thermal
<br />electric power produhion is increasingly im-
<br />portant to the economy of the area.
<br />,
<br />Irrigation accounts;for the largest use of wa-
<br />ter, nearly 80 percent of the total basin use.
<br />About 240,000 acreslof land are irrigated in an
<br />average yea r.
<br />
<br />. LOWER COL~RAOO RIVER
<br />
<br />Mainstream below Lee ferry, Arizona-
<br />California-Nevada: ThelColorado River has a
<br />length of over 700 mil~s and a drainage area of
<br />132,300 square miles!within the lower Col-
<br />orado River system in ~he United States. From
<br />Lee Ferry to the headw~ters of Lake Mead,
<br />the river flows through the spectacular can-
<br />yons of northern Arizona,including the Grand
<br />Canyon. At Lake Mead, idiversions are made
<br />to the rapidly expanding North Las Vegas-Las
<br />Vegas-Henderson-Bould~r City area for munici-
<br />pal and industrial purposes. Below Lake Mead,
<br />the river courses throug~ broad alluvial val-
<br />leys interspersed with mbuntain chains.
<br />Lakes Mohave and Hava~u provide flood con-
<br />trol and regulatory storaae below Lake Mead.
<br />
<br />In addition, Lake Havasu provides a fore bay for
<br />pumped export to the Metropolitan Water Dis-
<br />trict of Southern California and Lake Mohave
<br />reregulates Hoover Dam releases for power
<br />production and for deliveries to Mexico.
<br />Lesser structures downstream include Head-
<br />gate Rock, Palo Verde, Senator Wash, Impe-
<br />rial, and Laguna Dams. laguna and Senator
<br />Wash Dams provide reregulation capacity
<br />while the others are used principally for diver-
<br />sion.
<br />Diversions below Lake Mead for agricul- ,
<br />ture, municipal and industrial, power, export,
<br />and other purposes are of the magnitude of 9
<br />to 9.5 million acre-feet annually. A consider-
<br />able portion of these diversions is satisfied
<br />from upstream return flows. Yuma and Lake
<br />Havasu City in Arizona, and Needles and
<br />Blythe in California are the major cities
<br />along the mainstream below Lake Mead. Cur-
<br />rent irrigated land adjacent to the
<br />mainstream is estimated to be about 351,000
<br />acres. There has been a significant annual in-
<br />crease in the diversions for municipal and in-
<br />dustrial purposes, particularly to Nevada.
<br />Little Colorado River, Arizona-New Mexico:
<br />The little Colorado River drainage area oc-
<br />cupies a large part of northern Arizona and a
<br />portion of west-central New Mexico. It rises on
<br />the north slopes of the White Mountains about
<br />20 miles above Springerville, Ariz.; has a
<br />mainstream length of about 356 miles; and
<br />joins the Colorado River on the east bound-
<br />ary of Grand Canyon National Park about 78
<br />miles downstream from Glen Canyon Dam.
<br />A series of saline springs near the mouth
<br />produce an estimated 160,000 acre-feet of
<br />water annually. The Geological Survey gaging
<br />station near Cameron is located in the
<br />Navajo Indian Reservation about 45 miles
<br />upstream from the mouth. Streamflow is un-
<br />dependable and erratic, SUbject to flash
<br />floods of considerable magnitude. During the
<br />period 1971-75, water year outflow at the
<br />gaging station near Cameron varied from the
<br />floodflow of 815,900 acre-feet in 1973 to
<br />28,300 acre-feet in 1974. Only a minor de-
<br />velopment of the ground water has occurred
<br />because of low yields and poor quality. Ex-
<br />cessive erosion and sediment deposition plague
<br />7
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