The Center for Robot-Assisted Search and Rescue (CRASAR) assisted the Ventura County Fire Rescue Department with the January 2005 La Conchita, California, mudslide response. CRASAR provided commercially available urban search and rescue robots and expert operators which were deployed twice into damaged structures. The waterproof robots were able to tolerate wet conditions but proved unable to handle the densely packed rubble, vegetation, and soil and failed within two and four minutes, respectively on their two deployments. Informal interviews were conducted with responders as well. The experience forms a descriptive study of what mudslide responses are like, what tasks robots are needed for, how the rescue robots performed, and how responders viewed the robots. Our observations are captured in fourteen findings on robot performance (3), domain characteristics of mudslides (8), and general rescue robot design issues (3). These findings are expected to be of interest to robot designers, software developers, and the human-robot interaction communities. The experience at La Conchita illustrates that terrain understanding, critical for both robot design and for control, remains an important open research question for rescue robotics. © 2008 Wiley Periodicals, Inc.