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<br />2 <br /> <br />OVERVIEIO/ OF THE STUDY AREA <br /> <br />THE STUDY MEA <br /> <br />" <br />n As defined by the V,S, Water Resources Council (WRC) , the Upper <br />... Colorado River Regioa (hereinafter called "the Region") includes the <br />,~ Upper Colorado River Basin and the Great Divide Basin, which is a closed <br />basin in Wyoming,l Total drainage area of the Region, which covers about <br />45 percent of the Colorado River Basin, is 113,496 square miles <br />(72,600,000 acres), Dimensionally, the Region extends about 550 miles <br />north-south and 350 miles east-west to encompass portions of the states <br />of Wyoming, Colorado, Utah, New Mexico, and Arizona, <br /> <br />The Region may be disaggregated into the usual collection of poli- <br />tical subdivisions (states, counties, etc,) or physical subdivisions <br />(river basins, watersheds, etc.), With respect to political subdivisions, <br />this report ;.-ill refer to the multi-county "aggregated subareas" (ASAs) <br />used in the WRC 1975 Water Assessment. In this context, the hydrologic <br />boundaries of the Region are approximated by the political boundaries of <br />ASAs 1401, 1402, and 1403 (fig, 2.1). Much of the background information <br />found in this chapter, and elsewhere in this report, is presented on an <br />ASA basis, <br /> <br />. <br /> <br />The WRC has also divided the Region into t,ater Accounting Units (WAUs), <br />which are contiguous with the major river subbasins in the Region (fig, 2,2), <br />Figure 2.2 also shows the U.S. Geological Survey stream gauging station that <br />is nearest to the outflow point of each WAD, These gauging stations will <br />be referred to throughout this report, especially as they relate to hydro- <br />logic analyses, <br /> <br />For the purposes of this l3(a) assessment, the WAUs in the Region <br />have been further subdivided into study subunits (SSUs). This was done <br />in order to facilitate the compilation of water depletion data from indi- <br />vidual states and to keep an accounting of each state's depletions for <br />interstate compact purposes (see fig, 2.3). <br /> <br />1. Throughout this report the terms "Upper Colorado River Region" (or <br />"Region") and "Upper Colorado River Basin" (or "Basin") are used inter- <br />changeably. ~bile not identical areas, the differences in data that arise <br />by specifically including or excluding the Great Divide Basin are so small <br />as to be insignificant. <br /> <br />2-1 <br /> <br />.. <br />