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uranium, and high-grade oil shale (estimated to contain more than 1.5 trillion barrels of oil). Oil shale development holds many possibilities for social and economic growth. Although large scale plans for oil shale development have already been made, implemen- tation has presently been suspended until economic conditions change. Topography in the Rangely area is extremely diverse, and includes dissected plateaus, sharp ridges, abrupt cliffs, and rugged bad- lands that are interspersed with open valleys, meadows, and basins. The presence of underlying rock layers with wide differences in resistance to erosion has been the principal factor in the evolu- tion of these varied landforms. Erosion in the rolling shale hills and badlands around Rangely is severe. Deep and extensive gullying along drainageways and narrow valleys is of considerable agri- cultural significance. In many locations, dissection by gullies severely limits use of the land, and bridging gullies increases highway construction costs. Climate in the Rangely area is classified as semiarid, with rela- tively warm summers and cold winters. The mean annual temperature is 460F, with extremes of -370F and 1060F. The lower valley of the White River near Rangely has a frost-free period with an average length of 124 days per year. Average annual precipitation varies from 50 inches in the headwater regions of the White River Basin to less than ten inches at Rangely. Normally, approximately 40 percent of the annual precipitation occurs during August, September, and October. wintertime precipitation occurs as snow, and a deep snowpack usually accumulates in the high elevations. Summer rain- fall generally results from convective-type thunderstorms. These storms cause short-duration runoff that is characterized by high peak, low-volume flows. The flood plains of the streams studied are presently not exten- sively developed. There are various transportation facilities in the flood plains. There are some industrial and light residential land uses. However, continued and probably accelerated development due to increasing emphasis on mineral and energy extracting and processing is expected, and pressure leading to intensified flood plain use will undoubtedly accompany such development. 2.3 Principal Flood Problems Because of its particular geographic location, Rangely is subject to five different types of events that cause flooding: ice jams, rapid snowmelt, rain on snow, general rain, and local thunderstorms. The low permeability of the soils in and around Rangely is also a factor in producing flooding in the study area. Historically, ice jams, rain on snow, and local thunderstorms have caused the greatest flood damage in and around Rangely. Ice jams are formed by ice- flows piling up at an obstacle, such as an existing ice accumula- 5