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    <titleInfo>
      <title>Geologic Mapping Symbology, Freshwater Creek Watershed, California, 1999</title>
    </titleInfo>
    <name type="corporate">
      <namePart>California Geological Survey</namePart>
      <role>
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      </role>
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      <namePart>California. Division of Mines and Geology</namePart>
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      </role>
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    <abstract lang="eng" displayLabel="Abstract">This line shapefile contains geologic mapping symbology such as landslide scarps and direction of movement arrows, used for mapping watersheds in Freshwater Creek, located in Humboldt County, California. These data are represented at 1:24,000 scale. These data were derived from digital maps of landslide potential and geologic features in Humboldt County originally published in 1999 by the California Division of Mines and Geology (OFR 99-10 and OFR 99-10a). The data for the original mapping were compiled from multiple sources including published maps and reports, aerial photograph mapping, and reconnaissance geologic mapping.</abstract>
    <abstract lang="eng" displayLabel="Purpose">The maps/data are useful in preparation of Timber Harvesting Plans, and for use by land managers for identifying areas of potentially unstable ground. The maps/data serve as a guide to potential problem areas where more site-specific review is required.</abstract>
    <note lang="eng" displayLabel="Preferred citation">California Division of Mines and Geology and California Geological Survey. (2002). Geologic Mapping Symbology, Freshwater Creek Watershed, California, 1999. California Dept. of Conservation and California Geological Survey. Available at http://purl.stanford.edu/tq388jw2383.</note>
    <note displayLabel="Supplemental information">The discussion below was excerpted from OFR 99-10 and 99-10a.

The geology of the drainage is dominated by the Freshwater Fault.  This fault is 
considered a normal fault with blocks on either side stepping down to the west in a 
regional context.  Multiple strands of the fault appear to be present in the study 
area.  The fault is considered inactive because no evidence of movement after late 
Quaternary time has been observed along it.  The Freshwater Fault splits the 
watershed into two sections having different geologic conditions, topographic styles
and potentials for landsliding (Plate 1).

Much of the western half of the drainage has relatively steep topography underlain by 
gently dipping, interbedded mudstone, siltstone, sandstone and minor conglomerate of 
the Wildcat Group (early Pleistocene to late Miocene). These rocks are typically prone 
to shallow debris flows/slides and occasional translational/rotational rock slides.  
The Wildcat Group in this part of the drainage rests uncomformably atop interbedded 
sandstone and shale of the Yager Formation (early Tertiary).  The Yager Formation dips
steeply to the northwest (Plate 1).  Only one translational/rotational rockslide was 
identified in this unit.  Several lineaments were noted on the aerial photographs 
throughout this part of the drainage, but no faults are indicated.

The geology of the eastern half of the drainage is complex and most of the larger 
translational/rotational landslides and earthflows are found there.  The western third 
of this area is underlain by Wildcat Group rocks that rest unconformably atop dense 
sandstones and shales of the Yager Formation and Coastal Belt of the Franciscan 
Assemblage (PLATE 1).  The contacts between Yager and Franciscan rocks probably 
represent multiple strands of the Freshwater Fault (Keith Knudsen, May 1999, personal 
communication).

The remainder of the eastern half is dominated by a series of northeast-dipping 
thrust faults.  These faults are considered inactive at this time because they are 
not indicated on the State of California Earthquake Fault Zone map (State of California, 
1983).  The thrust faults juxtapose irregular slabs of dense sandstone/shale and melange 
of the Coastal Belt of the Franciscan Assemblage.  The erosional contrast between the two 
units is seen as discrete bands of "hard" and "soft" topography that cut through the 
drainage in a north-westerly direction (Plate 1).

The characteristics and properties of the various rock units found in this area were 
taken into account during the assessment of relative landslide potential.  The primary 
sources of geological data used in preparing the relative landslide potential map are 
compiled on Plate 1 of Open-File Report 99-10.

The Relative Landslide Potential Map has been prepared to aid in resource management and 
general land-use planning.  It is not intended, nor should it be used for, evaluation of 
specific sites.  Site specific evaluations often require detailed engineering geologic 
studies and soil engineering investigations of the underlying soil and bedrock for proper 
planning of specific projects.

This map is derivative, based on the following: 1) the occurrence and distribution 
landslides, other types of slope failure, and features indicating slope instability 
(Plate 1, Open-File Report 99-10); 2) the geology of the area, including bedrock types 
and lithologic properties relative to slope stability and distribution of various earth 
materials, as well as the structural framework, such as the folded and faulted strata 
found throught the region; and 3) the relative behavior of slopes within the area as 
interpreted from analysis of historic aerial photographs and recent field observations.

Studies of the stability of specific sites commonly require development of quantitative  
data through laboratory testing of field samples.  This level of testing was not done for 
this regional evaluation.  In producing this map, it was assumed that actively sliding 
material has the lowest relative strength, and thus, the highest relative potential for 
landsliding of all the geological materials underlying the slopes.  Recent alluvial 
deposits in the valley bottom were assumed to possess the least potential for landsliding 
due to their flat slope.  The relative potential for landsliding between these extremes 
was evaluated subjectively based on aerial photograph interpretation, field observations 
and the following principal factors:

 The broad apparent stability characteristics of geological materials underlying 
        the slopes and adjacent lower-lying areas, as expressed in their natural 
        exposures and their observed responses to alteration by land-use activities.  
        For example, slopes that exhibit abundant evidence of landsliding or downslope 
        creep of the soil are considered oversteepened relative to the strength of the 
        materials that underlie them.

 Steepness of slopes, whether or not landslides are apparent.

 The presence of active or intermittent natural influences that tend to cause  
        slope failure.  These include gravity, climatic conditions, fluvial processes,  
        and the tendency of certain soils to shrink and swell under varying moisture 
        conditions.
    
These criteria are combined to yield the five-value scale used on the Relative Landslide 
Potential Map to indicate the comparative capacity of the slopes within the map area to 
resist failure by landsliding.

The map, Landslide Potential with Geologic and Geomorphic Features, Freshwater Creek, 
Humboldt County, California is a digital representation of the map, Geological and 
Geomorphic Features Related to Landsliding, OFR 99-10, combined with the map of Relative 
Landslide Potential, OFR 99-10a. 

Purpose:

The maps/data are useful in preparation of Timber Harvesting Plans, and for use by land 
managers for identifying areas of potentially unstable ground. The maps/data serve as a 
guide to potential problem areas where more site-specific review is required.
                             
Data Capture Procedures:

As noted previously, geomorphic features were mapped on stereo pair photographs and 
transferred to 7.5 minute quadrangle mylar overlays.  These overlays were scanned and 
converted to ArcInfo vector coverages.</note>
    <note displayLabel="WGS84 Cartographics">This layer is presented in the WGS84 coordinate system for web display purposes. Downloadable data are provided in native coordinate system or projection.</note>
    <subject authority="lcsh" lang="eng">
      <topic authority="lcsh" authorityURI="http://id.loc.gov/authorities/subjects.html">Faults (Geology)</topic>
    </subject>
    <subject authority="lcsh" lang="eng">
      <topic authority="lcsh" authorityURI="http://id.loc.gov/authorities/subjects.html">Landslides</topic>
    </subject>
    <subject authority="lcsh" lang="eng">
      <topic authority="lcsh" authorityURI="http://id.loc.gov/authorities/subjects.html">Watersheds</topic>
    </subject>
    <subject authority="lcsh" lang="eng">
      <topic authority="lcsh" authorityURI="http://id.loc.gov/authorities/subjects.html">Landslide hazard analysis</topic>
    </subject>
    <subject lang="eng">
      <geographic>California, Northern</geographic>
    </subject>
    <subject lang="eng">
      <geographic>Humboldt County (Calif.)</geographic>
    </subject>
    <subject lang="eng">
      <geographic>Freshwater Creek (Calif.)</geographic>
    </subject>
    <subject>
      <temporal encoding="w3cdtf">1999</temporal>
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    </subject>
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      <dateIssued encoding="w3cdtf" keyDate="yes">2002</dateIssued>
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      <publisher>California. Dept. of Conservation.</publisher>
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        <title>Maps and GIS data for the Watersheds mapping series. Map set 3, Digital representation of OFR 99-10 &amp; OFR 99-10a, Freshwater Creek, Humboldt County, California</title>
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