COLLABORATIVE LANDSLIDE INVENTORY MAPPING IN DOUGLAS COUNTY, OREGON

Landslides are a significant geologic hazard in Oregon. In order to reduce the risk from future landslides, an accurate and complete landslide inventory is fundamental. In 2015, the Bureau of Land Management (BLM) Coos Bay District began a multi-year collaborative landslide inventory mapping project with the Oregon Department of Geology and Mineral Industries (DOGAMI). The BLM Coos Bay District has land in Douglas, Coos, and Curry counties in Oregon. All three counties have relatively weak geologic units, steep topography, high annual precipitation, dense vegetation, and are subjected to large subduction zone earthquakes and thus have relatively high landslide hazards.

The project has two primary goals: 1) create a detailed landslide inventory and 2) provide real world training to students studying geologic hazards. Three Portland State University geology students have benefitted from this opportunity. One of the students was hired by the Colorado Geologic Survey to work on landslide hazard reduction in Colorado.

We have completed mapping in 10 watersheds. The watersheds cover an area of 278.32 square miles. We mapped 1,163 historic points and 2,984 landslide deposits. The landslide deposits cover 41.05 square miles of the watersheds which is approximately 15% of the total study area. However, the individual watersheds range in landslide density from approximately 2% to 32%.

In order to make these data easily accessible by anyone, they will be published as a DOGAMI Open File Report and then compiled into the next Statewide Landslide Information Database of Oregon (SLIDO) release.