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~ lV:' C ... Watershed Characteristics l:. Topography and Geology The topography of the watershed ranges from an area of gently sloping mesas and benches to steep and very steep mountainous land along the upper Smi th Fork Ri ver. The mesa area consists of two parts whose drainage is divided between the Smi th Fork and the North Fork Rivers. The south mesas are drained by Iron Creek and Poison Spring Gulch into the Smith Fork River. The Smith Fore River flows westward along the base of the sharp cliff that separates the two areas. An uplift forms the and Mi ssouri Flats. Creek. north mesa area commonly referred to as Grandview Mesa These mesas are drained by Allen Gulch and Cottonwood Other project lands are located south of the Smi th Fork River and east of Crawford Reservoir. A few small fields are located in the canyon bottom. The Crawford Reservoi r si te is on Iron Creek just above its confluence wi th the Smi th Fork River. Iron Creek drainage is characterized by some relatively flat alluvi al be ttoms surrounded by a large area of steeply rolling to steep, hilly terrain and raw shale escarpments. The major portion of the lower watershed area is Mancos shale formation. The hi gh mountains at the upper reaches of the Smi t.h Fork River are made up of early Tertiary intrusive rocks, while the high lIlOuntains at the head of the Iron Creek drainages are formed frolll a volcanic agglomerate and breccia. Precipitation and Runoff The average annual precipitation varies from about eleven inches at Crawford to nearly thirty inches in the higher mountains. Approximately 50 percent of the precipitation is received as snow. The month of June receives the least precipi tation. Some high-intensi ty rainstorms occur in July, August and September. Flood stages can be expected from snow mel t during May and June, and from high-intensiq rains in July, August and September. Vegetation Vegetative cover by principal type and condition is shown in table 15. - 49 -