San Francisco Bay Area

Landslide and debris-flow activity in the San Francisco Bay region following the February 2-3, 1998 storm.

On February 4, USGS scientists Steve Ellen and Mark Reid conducted a ground reconnaissance of a portion of the San Francisco Bay region. They traveled up the east side of the Peninsula to southern Marin County, then to the east Bay and down the range front on the east side of Hayward and Fremont to Niles Canyon. They were looking for landslides and debris flows that could be directly attributed to this storm, and in particular to ascertain the timing of events. Also, on February 4, Angela Jayko (USGS scientist) examined the coastal (west) side of the Santa Cruz Mountains and the Pescadero area.

Landslide and "mudslide" activity has been extensively reported in the news media following heavy rains on February 2-3, 1998. A number of scattered, slow-moving landslides have been active over the past few weeks in San Francisco, Oakland, and elsewhere in the Bay region. As most of the area has experienced about 200% of normal rainfall to date, these landslides are probably related more to the wet winter, and less to the effects of this particular storm. However, based on limited ground reconnaissance, scattered slope movements directly related to the storm did occur.

Debris flows directly triggered by the storm have impacted a number of homes and properties. Many of these may be partially related to human modifications, such as altered drainage and fills. A few debris flows on natural slopes were noted on San Bruno Mountain. A large number of debris flows were noted in the hills behind Hayward, Union City, and Fremont. Perhaps 20 debris flows were also noted on the west side of the Santa Cruz Mountains. One fatality resulted from a debris flow impacting a house in Loma Mar near Pescadero.

It is anticipated that many landslides will develop over the next several months in this area, due to the exceptionally wet winter. USGS landslide researchers will continue to perform reconnaissance and assist in the hazard assessment of this winter's California storms.

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Photo 1 House destroyed by a debris flow triggered by intense rains on February 2, 1998 in Marin County.
Photo 2 Gully retreat threatening evacuated houses in Daly City.
Photo 3 Debris flows on natural hillslopes behind Union City triggered by the February 2-3 storm.
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Photo 4 Debris flow scar above destroyed house in Marin County.

Landslide Location Map

Contact Information

For more information, please contact:

The National Landslide Information Center