USGS - Preliminary Interpretation of Pre-2014 Landslide Deposits in the Vicinity of Oso, Washington, By Ralph A. Haugerud.
“High-resolution topographic surveys allow fairly precise mapping of landslide deposits and their relative ages. Relative ages are determined by cross-cutting relations and the amount of smoothing—more smoothed slide deposits are older—of these deposits. The Tulalip Tribes, in partnership with the Puget Sound Lidar Consortium, acquired a high-resolution lidar (light detection and ranging) survey of the North Fork Stillaguamish River valley in 2013. This report presents a preliminary interpretation of the topography of this area using the lidar data at a scale of 1:24,000.”
- See also the Wikipedia entry on Oso, Washington