MAPPING AND ATTRIBUTING LANDSLIDES WITH ARCGIS FOR LAND MANAGEMENT IN TWELVEMILE CANYON, MANTI-LASAL NATIONAL FOREST, UTAH

Twelvemile Canyon in central Utah is an area of extensive landsliding that has historically impacted Manti-LaSal National Forest lands. Landslides in the canyon range from small rock falls and debris flows to large earth flows up to 2.5 miles long. We use ArcGIS to map and store landslide information for land-management analysis and evaluation. Much of Twelvemile Canyon is underlain by the landslide-prone North Horn Formation that is dominantly shale and contains the majority of mapped landslides. Landslides are also present in the overlying Flagstaff and the underlying Price River Formations which contain shale interbeds. We map and inventory prehistorical and historical landslides at 1:24,000-scale using stereo aerial photographs and orthophoto imagery. We utilize several sets of aerial photos to characterize historical landside activity for a 66-year period from 1940 through 2006. The characteristics of each landslide are attributed and stored in a geodatabase for analysis.

The landslide inventory shows the location of landslides, and since future landsliding is generally based on past landslides, the landslide inventory is useful for predicting future landsliding for use in land-management analysis. ArcGIS is also a spatial analysis tool useful for understanding the relationship between landslides and specific land-management elements, such as streams, roads, bridges, campgrounds, trails, or timber sales. The geodatabase can be queried to determine which landslides intersect or underlie a specific land-management element. For example, landslides crossed by a road or within a timber sale can be quickly determined. Understanding the extent and relative activity of landslides and their potential impacts allows for informed land-management decisions and how to best anticipate problems resulting from future landslide movement.