Landslides can dam rivers and require rapid response to mitigate catastrophic outburst floods. Here we present a workflow to map landslide dam formation susceptibility at a regional scale. We define a probabilistic function that combines river valley width and landslide volume to efficiently determine the likelihood of a landslide dam or ‘damability’. We combine damability values with landslide susceptibility to find landslide dam susceptibility. The valley width measurements are automated using a new elevation threshold-based algorithm. Landslide volume is represented as a statistical distribution from mapped landslides. We verify and apply our approach to the Oregon Coast Range, USA and find high susceptibility in river headwaters and generally steeper terrain, which in this case correlates with more resistant lithologies. We also estimate volumes of the potential dammed lakes and find that most rivers with high dam susceptibility are less likely to impound large lakes, because they have low drainage areas. However, widespread susceptibility, and the critical potential impacts from exceptionally large landslides, suggest this hazard should be considered in the Pacific Northwest. The damability function workflow can readily ingest new data and can be applied more broadly to assess future landslide dam hazards.