California releases landslide risk map

San Francisco mountain towns at highest risk

SAN FRANCISCO (UPI) | May 24, 2011

"Landslides are just a natural part of the landscape, but they get to be a problem when people build around them"

—Chris Wills, California Geological Survey

Communities in the mountains surrounding the San Francisco Bay Area are in more danger from landslides than other places in California, scientists say.

A map of the state's most landslide-prone areas released Thursday by the California Geological Survey is an effort to determine the most vulnerable spots in the event of a once-a-century superstorm, the San Francisco Chronicle reported.

The map utilized a database of 57,000 historic landslides to analyze the rocks, soil and steepness of terrain around the state.

"The goal in this was to develop a scenario for a major storm," said Chris Wills, the Geological Survey's supervising geologist. "We felt it was important to get this basic information out so people can look at what are the most susceptible areas."

The map shows the North Coast between Sonoma County and Oregon, and the Coast Range between San Francisco and Los Angeles, are the most susceptible areas in the state.

About two-thirds of Marin and Sonoma counties are identified as high-hazard areas. The Santa Cruz Mountains and the East Bay hills are also highly susceptible to landslides, the map indicates.

More than 100 Californians have been killed by landslide debris flows in the past 25 years.

Ten people were killed, 14 were injured and 31 homes were destroyed by a 30-foot wall of mud in Ventura County north of Los Angeles in 2005.

"Landslides are just a natural part of the landscape, but they get to be a problem when people build around them," Wills said. "Now that we have the susceptibility map, we can take any storm or any storm season and see what the likelihood of a major landslide is."

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