California Division of Mines and Geology

Geologic mapping and El Niño in southern California:

Understanding the maps describing debris-flows susceptibility

The U.S. Geological Survey's debris-flow maps for Southern California describe areas prone to damage during high-rainfall seasons, such as El Niño events. The maps are constructed at a scale of 1:100,000 and are suitable for general planning purposes but not for site-specific applications such as determining the hazard for a single building. The example below shows what information you can get.

Example: Palos Verdes

What does the map show?

• The gray area shows land, with different shades of gray giving the effect of shaded relief showing mountains, canyons, and plains
• Black lines show main roads and streets.
• Bright yellow areas indicate slopes that are prone to possible debris flow activity.

Getting the maps: Large JPEG files of the maps.

Getting the maps: Smaller, low resolution files.

Detailed maps: Comparing past debris flows and the predictions.

How the maps are made

Photos of debris flows and landslides

For further information, contact David Miller

http://geology.wr.usgs.gov/wgmt/elnino/scampen/mapexamp.html, 7 January 1998, Contact: El Niño Web Team