CGS/CDF Watersheds Mapping

A Cooperative Effort of the California Department of Conservation and California Department of Forestry and Fire Protection

Translational/rotational landslide, Humboldt County.
Photo by Tom Spittler.

During the early 1980s, under the provisions of Section 208 of the Federal Water Pollution Control Act, the Environmental Protection Agency (EPA) funded a number of water protection projects that involved the geologic mapping of sensitive watersheds along California's north coast. Since then, the California Department of Conservation, California Geological Survey (CGS) has been contracted by the California Department of Forestry and Fire Protection (CDF) to produce maps for parts of Mendocino, Humboldt, and Del Norte counties, and other selected watersheds throughout the state (see Watersheds Index Map).

The long-range goals of the watersheds mapping projects are: 1) to retain productive forest soils, reduce sedimentation of north coast streams, and protect fish habitat; 2) to provide planning guides for timber harvesting and other forest management activities; 3) to comply with the Clean Water Goals of the Federal Water Pollution Control Act; and 4) to achieve the objectives in the state’s water quality control plans and other forest practice rules.

The maps provide information on the geology and geomorphic features affecting landslides for each of the watersheds studied. Physical characteristics that can be correlated to landslide potential, soil erosion potential and streambank erosion potential were mapped at a scale of 1:24,000. Sixty 7.5-minute quadrangles were completed by DMG between 1981 and 1985. Additional mapping in selected watersheds identified by CDF includes interpretative evaluations of relative slope stability for long-term planning purposes (see DMG Note 40).

Landslides  

Four categories of active and dormant landslides are depicted on the maps. They include debris slides, translational/rotational slides, earthflows, and debris flows and torrent tracks. Debris slide amphitheaters and slopes and inner gorges are not technically landslides, but features formed by landslides processes. These too are included on the watersheds maps. In some places, complex landsliding causes irregular ground surfaces that are indistinguishable or too small to map at the 1:24,000 scale. Such areas are depicted on the maps as disrupted ground or in those watersheds where relative slope stability maps exist, areas of extreme, high, moderate, and low relative stability are identified. Factors affecting landslide potential in these areas are described in DMG Note 50.

Use of the Maps

Debris flow following rotational/translational landslide, Mendocino County. Photo by Julie Sowma-Bawcom.

Watersheds maps are available to land managers, planners, and the public for uses aimed ultimately at the reduction of erosion and landsliding, and the enhancement of water quality.

The maps and legends will enable users to: 1) recognize and "flag" areas of potentially unstable ground, and 2) foresee and minimize potential problems in these areas. The maps should be most useful for identifying unstable and erosion-prone areas on a regional scale, and in the preparation of large scale, long-range management plans that use geologic information to minimize environmental impacts. The maps should not be used a substitute for on-the-ground site-specific studies (see DMG Note 45), but rather for identification of possible problem areas that need on-the-ground attention prior to development. Thus, identification of a landslide or geomorphic feature on the map does not preclude logging or other types of land development at that particular sight.

Availability

Hard copies of the watersheds maps may be  referenced at all three CGS offices and referenced in Sacramento. For office locations, see the Contact CGS web page. Information on obtaining digital versions of the maps is available at the CGS Publications page. Other types of watershed data may be viewed at the CDF web site http://frap.cdf.ca.gov under Watersheds.
 

Index to Landslide Mapping

Updated and now available on-line: Index to Published Landslide Maps, California Coast Ranges, Monterey County and North for Use in Timber Harvest Plan Preparation on Non-Federal Land, by Davies, R.I. and Spittler, T.E.: CGS Special Publication 120: $8.00 for printed copy. Available for free download as a 635 KB PDF file. Errata sheet (67 KB) also available separately.

CGS/CDF Watersheds Mapping Projects

To preview/download a Watersheds Map or view the metadata, click on desired map quadrangle on Index Map below or click on map name on Index List. Both geologic and geomorphic features maps are provided in black/white format. In the future, colored geologic features maps will be provided, and will be posted to this site as they become available.

Printing Notes: Map colors may differ somewhat between computer monitor and hardcopy print. To achieve the best quality print of black and white as well as colored maps it is suggested that the viewer use an inkjet printer. If using a laser printer, set graphics mode to vector (not raster). For large format plotting, paper size should be set to Arch E. Adobe Reader®  is required to view these maps.  

GIS Data

GIS Data for this project is available on CD-ROM from CGS Publications under the listing for "CD 99-002  North Coast Watershed Mapping".. Alternatively, for users with T1 or faster Internet access, the complete set of GIS data for this project may be downloaded from this web site.

NOTE TO GIS USERS CONCERNING PUBLICATION DMG CD 99-002 1999

An error exists in the geomorphology export file geomorph.e00 on the CD version of this data set. To allow this file to be imported into ArcGIS please follow these steps:

1. Copy the file (79,470 KB) to your hard drive.
2. Remove the read-only restriction. To do so, right-click on the file. Left-click on Properties. Under Attributes, click the Read-Only box to remove the check and click the Apply button.
3. Open the geomorph.e00 file using an ASCII text editor. Search for "-3," and replace it with "-3." Save file. This will allow the file to import into ArcGIS.

CGS/CDF Watersheds Mapping Index Map