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Elevations in the Rifle Creek basin range from approximately 5,300 feet at the Colorado River to approximately 9,900 feet in the higher headwater ranges of the basin. vegetation in the upper Rifle Creek basin consists of aspen, conifers, and a moderate cover of native grasses. In the lower portion of the Rifle Creek basin and in the basins of Hubbard Gulch and Govern- ment Creek, vegetation consists of sagebrush, juniper, pinon, greasewood, and a sparse cover of native grasses and forbs. The climate of the Upper Colorado River basin can be characterized as semiarid, except in the higher elevations where precipitation is moderately heavy. Precipitation ranges from less than 10 inches per year in the lower valleys to more than 50 inches per year on the higher peaks. Most precipitation over the basin occurs as snow during the winter and early spring_ The Rifle Creek watershed is subjected to cloudburst activity with high-intensity rainfall of short duration during the summer and fall. Average annual temp- eratures vary from less than 320F in the high headwater areas to approximately 500F in the lower valleys. The surface cover of western Colorado ranges from barren rock to deep, fertile, friable loams and clays of good to excellent quality for plant growth. Along the north side of the Colorado River, near Rifle, is a prominent escarpment known as the Roan or Book Cliffs. Most of the area has fairly deep soils and steep slopes. Mancos shale outcrops follow West Rifle Creek. Sedimentary forma- tions are nearly horizontal in the upper part of the Rifle Creek basin. The commercial section of Rifle is situated in a narrow, shallow valley at the junction of Rifle and Government Creeks and north of the Colorado River. The Rifle Creek flood plain has been intensely developed and is devoted largely to residential, commercial, and civic uses. Development in the study area can be expected to continue, because the city serves as the local center for retail trade, transporta- tion, and the recovery and processing of mineral resources. Accord- ing to U.s. Census Bureau figures, the population of Rifle increased from 2,150 in 1970 to 3,215 in 1980 (Reference 1). If a major breakthrough were to take place in the production of oil from the vast oil shale reserves of the area, the population could be expected to expand greatly. 2.3 Principal Flood problems The Rifle Creek basin has a long history of floods, but limited definitive data on specific floods are available. Damage from 4