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The western portion of El Paso County is in the Rampart Range of the Rocky Mountains, while the remainder is in a high plains region. Elevations range from 14,110 feet to 5,150 feet in southern El Paso County. Within El Paso County, the high plains are characterized by gently sloping plains, whereas the mountain and foothill regions are made up of rough and broken terrain. Glacial deposits remain in many of the valleys above 9,500 feet. Usually the aspen-, spruce-, and pine-covered narrow canyons are straight, steep walled, and well drained. The foothills are a narrow transition from the mountain to the high plains. This transitional area varies from rough, steep ridges to narrow, gently sloping mesas with pine, pinion, cedar, and oak cover. The rolling high plains terrain is rough, broken, and sparsely vegetated. Typical of the semiarid high plains, the vegetation is predominantly brush, cactus, and mostly native grasses. Coniferous and deciduous trees grow along the various creek banks. Soils of the region are generally gray desert soils with areas of sandy soils on the plains. Alluvial gravels cap the foothill mesas, and arid-subhumid lithosols are in the mountains and foothills. Generally, the mountain and foothill areas have high coefficients of runoff, steep stream gradients, and narrow flood plains. High plains areas generally have a lower coefficient of runoff, gradual elevation changes, and relatively broad streambeds and flood plafns. Within the region, precipitation varies considerably because of elevation, major wind currents, and local geographical features. winter storms, typically from the northwest, tend to lose their moisture on the western side of the Rocky Mountains. The major precipitation comes through late spring snows, influenced by south- easterly winds, and from summer thunderstorms. Annual precipitation varies from 8 inches to a high of 20 inches in the mountainous areas. 2.3 Principal Flood Problems Most of the flood-producing storms in the region occur during May through August. The most severe storms occur in the transitional periods of late spring or early fall when polar air intrusions are more intense. Isolated summer thunderstorms are frequently severe, but limited in areal extent. Available records indicate ~hat snow- melt has not contributed significantly to flood occurrences in the study area. Floods are characterized by high peak flows, moderate volumes, and short durations. Historical flooding information is not available for the immediate Green Mountain Falls area. The May 1935 flood is the largest recorded flood (55,000 cubic feet per second) on Fountain Creek 5 ~~d~~ ~