Geomorphic mapping and topographic analysis of the Barker Reservoir Area, Utah

A wide variety of geomorphic processes have interacted to produce a complex landscape in the High Plateaus of Utah. This study centers on the high southern slopes of the Aquarius Plateau in the drainage basin of North Creek where the landscape is primarily the result of mass-wasting processes and the subsequent modification of the mass-wasting deposits by fluvial action. The High Plateaus are composed of essentially flat-lying sedimentary strata overlain in places by volcanic rocks and separated by the scarps of highangle normal faults with the downthrow primarily on the west side. The climate and vegetation associations of the High Plateaus are largely a function of altitude. Access to the study area is provided by one road, which follows North Creek to Barker Reservoir. There are no permanent residences in the area and recreation and cattle grazing are the only land uses. Objectives of the study are primarily to inventory the landforms of the area and discuss the causative geomorphic processes as well as to develop a useful geomorphic mapping technique for mass-wasting phenomena and to apply the technique to aid in the development of a highly unstable area. Field work was conducted during the months of July and August in 1970. The area was mapped during daily traverses into the various, sections and with the aid of aerial photographs obtained from the U.S. Forest Service. An active earth-flow was discovered in Holbys Bottom and was mapped in detail at a scale of 1 : 2,000 using compass, tape, and Abney level. In the laboratory, slope stability, vegetation, and drainage were mapped by analysis of aerial photographs aided by recorded field observations. Data for hypsometric analysis and analysis of closed contours, depressions, and relief of the landslide bench was obtained from a topographic map of the area. The surface of the Aquarius Plateau is bounded by a 17,5 kilometer scarp which isflanked over most of its length by talus slopes. Retrogressive landsliding of large blocks away from the plateau surface has formed a landslide bench below and adjacent to the full length of the scarp. Headward erosion by streams has steepened slopes near the edge of the landslide bench. Saturation of the debris at the edge of the bench by groundwater has resulted in its failure and downslope movement over these slopes until they have become mantled with landslip deposits. This surface is termed the landslide bench slope and on it are debris-flows, slow rock-fragment-flows, and an active earth-flow, The landslide debris below the landslide bench and bench-slope is continually being reworked by slope wash and channel flow and is being redeposited in some areas as pediment gravels. Torrential boulder deposits are located in the stream bottoms of the major streams. Slope stability of the study area has been mapped in four classess 1) active slopes, 2 ) highly unstable slopes, 3) slopes of questionable stability under present conditions, and 4) slopes which are stable under present conditions. Vegetation in the study area is primarily associated with climatic factors involved with altitude, slope exposure, and moisture conditions. On the landslide bench, vegetation associations with surficial materials also exist. Drainage in the study area reflects the adaption of drainage lines to landslide topography and the subsequent modification of the landslide topography by fluvial erosion. Two types of hypsometric analysis were conducted in the study area. Hypsographic curves were constructed for stream basins whose morphology was due primarily to landsliding and also for stream basins in which the landslide deposits had been removed by erosion. Analysis of closed contours, depressions, and relief of the landslide bench was undertaken to give quantitative expression to various topographic characteristics of the landslide bench and to provide comparative factors. Current land use activities in the study area show minor adverse effects but increased intensity of current uses or expansion of the number of land-use activities may have serious adverse effects