J. W. Godt J. A. Coe 2001 On February 2 and 3, 1998, a rainstorm generated by the 1997-98 El Nino moved through the San Francisco Bay region of California triggering widespread slope failures. In the Walpert Ridge area of Alameda County 531 debris flows were triggered by the storm. These data depict the debris flows and landslides as polygons. The landslide polygons were mapped from 1:30,000 aerial photography using a PG2 photogrammetric plotter. The mapped debris flows and landslides were digitized manually in ArcInfo. application/pdf 10.3133/mf2384 en U.S. Geological Survey Debris flows triggered by the El Nino rainstorm of February 2-3, 1998, Walpert Ridge and vicinity, Alameda County, California reports