Landslide

Description:

Slides and earth flows are landslides that can pose serious hazard to property
in the hillside terrain of the San Francisco Bay region. They tend to move
slowly and thus rarely threaten life directly. When they move -- in response
to such changes as increased water content, earthquake shaking, addition of
load, or removal of downslope support -- they deform and tilt the ground
surface. The result can be destruction of foundations, offset of roads, and
breaking of underground pipes within and along the margins of the landslide,
as well as overriding of property and structures downslope.

The best available predictor of where movement of slides and earth flows might
occur is the distribution of past movements (Nilsen and Turner, 1975). These
landslides can be recognized from their distinctive topographic shapes, which
can persist in the landscape for thousands of years. Most of the landslides
recognizable in this fashion range in size from a few acres to several square
miles. Most show no evidence of recent movement and are not currently active.
Some small proportion of them may become active in any one year, with
movements concentrated within all or part of the landslide masses or around
their edges.

These maps and databases provide a summary of the distribution of landslides
evident in the landscape of the San Francisco Bay region. Original
identification and map delineation of these landslides required detailed
analysis of the topography by skilled geologists, a task generally
accomplished through the study of aerial photographs. Such original landslide
maps are now available for most of the region at scales of 1:24,000 - 1:62,500
(Pike, 1997). The summary map presented here makes selected use of these
original maps and the 9-county compilation by Nilsen, Wright, and others
(1979) to provide a basis for initial evaluation of areas vulnerable to
slumps, translational slides, and earth flows in the region.

The summary map modifies and improves the compilation by Nilsen and Wright,
which was prepared from sources available in the mid-1970's. The generalized
landslide distribution shown on that map has here been improved in areas where
the 1970's sources were notably deficient (Figure 1), has been extended to
include Santa Cruz County, and includes the distribution of surficial deposits
that define landscape not generally vulnerable to these kinds of landslides.
The method of compilation and resolution of 1:125,000 (1 inch = 2 miles)
limits use of the map to regional considerations. For more detailed
information, see the maps listed by Pike (1997) or consult local officials or
private consultants.

Identifier:

https://spatial.lib.berkeley.edu/viewpublic/ark28722-s7qc7d

Creator:

U.S. GEOLOGICAL SURVEY

Publisher:

Menlo Park (Calif.) U.s. Geological Survey.

Provider:

University of California Berkeley

Resource Class:

Datasets

Resource Type:

Polygon data and Vector data

Subject:

Geology and Landslides

Temporal Coverage:

1997

Spatial Coverage:

Marin County (Calif.)

Access Rights:

Public

Format:

Shapefile