LANDSLIDE MAPPING AND ATTRIBUTING WITH ARCGIS FOR LAND MANAGEMENT IN THE MANTI-LASAL NATIONAL FOREST, CENTRAL UTAH

The Manti-LaSal National Forest in central Utah includes widespread landsliding that damages roads and campground facilities, and persistently degrades surface-water quality. Landslides range from small rock falls and debris flows to large rotational slides and earth flows up to 2.5 miles long. Our mapping at 1:24,000-scale includes a geodatabase with landslide spatial and movement information for use in land-management analysis and evaluation.

Our mapping area is in the Wasatch Plateau at the northern end of the Basin-and-Range/Colorado Plateau Transition physiographic province. Bedrock in the area is mostly flat-lying to west-dipping, cut by north-trending normal faults, and composed of landslide-prone units, including the Cretaceous Price River Formation, the Tertiary Flagstaff Limestone, and the Tertiary-Cretaceous North Horn Formation-a dominantly shale unit that contains the majority of our mapped landslides. The North Horn-associated landslides are generally large earthflows or complexes with rotational block and translational debris slide components, whereas the overlying, plateau-capping Flagstaff Limestone commonly produces rock falls.

We map and attribute landslides using stereo aerial photographs and orthophoto imagery to characterize historical landside activity for a 69-year period from 1940 through 2009. The characteristics of each landslide are attributed and stored in a geodatabase for analysis. The landslide geodatabase includes spatial, geologic, and qualitative activity information and is useful for ranking areas of potential movement. ArcGIS is also a useful analytical tool for discerning the relationship between landslides and specific land-management elements, such as streams, reservoirs, roads, bridges, campgrounds, trails, and timber. Querying the geodatabase can readily determine landslides that intersect or underlie a specific land-management element, such as landslides crossed by a road or within a timber sale. Understanding the extent and relative activity of landslides and their potential impacts allows for informed land-management decisions and improves anticipating problems resulting from future landslide movement.