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1. The San Juan and Dolores River Basins
<br />The San Juan and Dolores River basins lie in the southwest corner of Colorado, with the headwaters of
<br />both rivers originating in the San Juan Mountains. The San Juan River flows southwest to Navaj o
<br />Reservoir, where it leaves the state in Archuleta County. It continues to flow through New Mexico and
<br />Utah before reaching the Colorado River. The Dolores River basin is located directly north of the San
<br />Juan River basin. The Dolores River flows first southwest to McPhee Reservoir and then continues
<br />northward before exiting the state in Mesa County. The San Juan and Dolores River basins encompass
<br />all of San Miguel, Dolores, Montezuma and La Plata counties, and parts of Mesa, Montrose, San Juan,
<br />Hinsdale, Mineral, and Archuleta counties in Colorado. Figure 1.1 is a map of the basin.
<br />1.1. Physical Geography
<br />The San Juan River basin extends into portions - `~ ` '~~' `'` ~', ~~ ~ ~ ~ ' ~~ `~
<br />of New Mexico on the south and Utah to the ,~~~` ~ ~. f 4- ? ~ ~~~ ~ ~~ a , ~ ~ ~ 1 ° t
<br />west contributin a roximatel 23 000 s uare ~ ~` ~ , ~ ~ '~
<br />miles of drainage area to the San Juan River at '~ ~ ~_ ~~ a ~ , ~.~ ~ ~ Y'' ~• ;
<br />the gage in Bluff, Utah. About one third of this ~h ~~~
<br />area, or 7,200 square miles, lies within ~_~:~ . ~ ' ,~, ~ ~~ '~~~ ~ -~ ~~
<br />Colorado. Elevations within the basin range '~' "~~ ~ _ `~ .. _ - `~_
<br />from over 13,000 feet in the headwaters at the ~~ ~~.~ "'~~ '~'~~- '
<br />~~ < r > . ~ =
<br />continental divide, to about 4,050 feet near the ° - * ;~-.~
<br />,, ;~~-
<br />city of Bluff, Utah. The lowest point in the ~ ~~ ~~'.~~ ~~
<br />basin within Colorado is in the Four Corners --' ~. '-- -`~ = ky ~~_ ~ ~' "
<br />area, with an elevation at about 4, 800 feet. The Animas xtver viewed fi^om Na~ow wage xatlroad
<br />major tributaries to the San Juan River include
<br />the Navaj o River, Piedra River, Los Pinos River, Animas River, Florida River, La Plata River,
<br />Mancos River, and McElmo Creek. Average annual streamflow for years 1971 to 1991 in the San
<br />Juan River above Navajo Reservoir is about 427,500 acre-feet. Prior to completion in 1971 of the
<br />San Juan Chama project, which diverts water from the San Juan River basin to the Rio Grande basin
<br />in New Mexico, the annual average streamflow above Navajo Reservoir was 457,900 acre-feet. At
<br />the Bluff, Utah gage, the annual average streamflow is
<br />1,863,000 acre-feet. This value is not adjusted for flow
<br />regulation caused by Navajo Reservoir since 1962.
<br />The Dolores River rises in the San Juan National Forest
<br />near Bolam Pass, just north of the San Juan River basin.
<br />Some elevations around the headwater areas lie above
<br />13,700 feet. The river flows southwest to McPhee
<br />Reservoir where it turns to flow to the northwest until it
<br />leaves Colorado and eventually joins the Colorado
<br />River near Cisco, Utah. The drainage area upstream of
<br />the gage at Cisco is approximately 4,580 square miles.
<br />The drainage area upstream of the most downstream
<br />San Juan & Dolores River Basin Information 1-1
<br />Nlc Yhee Keservoir
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