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." ( ~ ) 'fI ~ (, Iio ,; l . - 4 - DESCRIPTION OF THE WATERSHED Physical Data Location.- Indian Wash Watershed is located in Mesa County in west-central Colorado and includes lands in the drainage basin of Indian Wash in and adjacent to the northeast portions of the City of Grand Junction, Colorado. The watershed contains 15.06 square miles (9,640 acres) and has a length of about 9 miles and an average width of 1.7 miles. The area lies along the north side of the Colorado River and is tributary to that stream. Indian Wash heads in the Little" Book Cliffs '~ortheast of Grand Junction and drains southward for several miles across desert rangeland to the High Line Canal, which is carried across the stream channel by a concrete flume with automatic spilling of excess water into the Indian vlash channel. Two sIndller drainages (Hartman Draw and Stub Draw) lie to the east of Indian Wash above the High Line Canal and are tributary to the Indian Wash channel through the diverting capacity of the High Line Canal. The area included in the watershed above the High Line Canal is 10.24 square miles or 68 peroent of the total watershed area. . Below the High Line Canal, Indian Wash follows a deeply incised channel for about 1 1/3 miles to the flume crossing of the Grand Valley Canal. From Orohard Avenue, whioh is a few hundred feet downstream from the Grand Valley Canal, the wash flows in a man-made channel to its confluence with the Colorado River. Although Indian Wash is an intermittent stream in its upper reaches, there is generally a small flow in its lower reaoh, which canes from waste water and return flow from existing irrigation canals and drainage systems. Physiography and Geology.- The watershed li~s within the Grand Valley portion of the Colorado Plateau physiographic province. The total relief in the area is about 2,300 feet. Elevations range from a maximum of about 6,800 feet on the high escarpment of the Little Book Cliffs at the north end of the watershed to about 4,550 feet at the junction of Indian Wash with the Colorado River. The steep face of the Little Book Cliffs averages 1,000 feet in height. Thick resistant sandstone layers of the Mesaverde group form the upper part of the Cliffs and relatively soft shale of the Mancos formation the lower part. Mancos shale underlies the remainder of the watershed. The Mancos is predominantly a relatively unifor.m silty olay shale. It weathers on the surface to a friable semipowdery mass that forms a sticky clay when wet. Same thin beds of hard siltstone and fine grained sandstone are present in the shale, as well as a few very thin bentonite layers. Seams of gypsum and calcite are common lOCAlly. .