Geologic Map Database of the El Mirage Lake Area, San Bernardino and Los Angeles Counties, California

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. Where did the data come from?
  2. What changes have been made?
• How reliable are the data; what problems remain in the data set?
  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
  5. How consistent are the relationships among the data, including topology?
• How can someone get a copy of the data set?
  1. Are there legal restrictions on access or use of the data?
  2. Who distributes the data?
  3. What's the catalog number I need to order this data set?
  4. What legal disclaimers am I supposed to read?
  5. How can I download or order the data?
• Who wrote the metadata?

Title:

Geologic Map Database of the El Mirage Lake Area, San Bernardino and Los Angeles Counties, California

Abstract:

This geologic map database for the El Mirage Lake area describes geologic materials for the dry lake, parts of the adjacent Shadow Mountains and Adobe Mountain, and much of the piedmont extending south from the lake upward toward the San Gabriel Mountains. This area lies within the western Mojave Desert of San Bernardino and Los Angeles Counties, southern California. The area is traversed by a few paved highways that service the community of El Mirage, and by numerous dirt roads that lead to outlying properties. An off-highway vehicle area established by the Bureau of Land Management encompasses the dry lake and much of the land north and east of the lake. The physiography of the area consists of the dry lake, flanking mud and sand flats and alluvial piedmonts, and a few sharp craggy mountains. This digital geologic map database, intended for use at 1:24,000-scale, describes and portrays the rock units and surficial deposits of the El Mirage Lake area. It was prepared as part of a water-resource assessments of the area, describing and interpreting surface geology that provides information to help understand distribution and extent of deeper groundwater-bearing units. The area mapped covers the Shadow Mountains SE and parts of the Shadow Mountains, Adobe Mountain, and El Mirage 7.5-minute quadrangles. The map database includes detailed geology of surface and bedrock deposits, which represent a significant update from previous bedrock geologic maps by Dibblee (1960) and Troxel and Gunderson (1970), and the surficial geologic map of Ponti and Burke (1980); it incorporates a fringe of the detailed bedrock mapping in the Shadow Mountains by Martin (1992).

1. How should this data set be cited?

   Miller, David M., and Bedford, David R., 2000, Geologic Map Database of the El Mirage Lake Area, San Bernardino and Los Angeles Counties, California: U.S. Geological Survey Open File Report 00-222, U.S. Geological Survey, Menlo Park, CA.

   Online Links:

   • <http://wrgis.wr.usgs.gov/open-file/of00-222>
   • <http://geopubs.wr.usgs.gov/open-file/of00-222>

2. What geographic area does the data set cover?

   West_Bounding_Coordinate: -117.690702

   East_Bounding_Coordinate: -117.501459

   North_Bounding_Coordinate: 34.735409

   South_Bounding_Coordinate: 34.499069

3. What does it look like?

   elm_browse.jpg (JPEG)

   Thumbnail

4. Does the data set describe conditions during a particular time period?

   Calendar_Date: 1999

   Currentness_Reference: ground condition

5. What is the general form of this data set?

   Geospatial_Data_Presentation_Form: vector digital data

6. How does the data set represent geographic features?
   1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • Complete chain (2651)
      • Entity point (955)
      • GT-polygon composed of chains (955)
      • Point (49)

   2. What coordinate system is used to represent geographic features?

      Grid_Coordinate_System_Name: Universal Transverse Mercator

      Universal_Transverse_Mercator:

      UTM_Zone_Number: 11

      Transverse_Mercator:

      Scale_Factor_at_Central_Meridian: 0.9996

      Longitude_of_Central_Meridian: 117.0

      Latitude_of_Projection_Origin: 0.0

      False_Easting: 0

      False_Northing: 0

      Planar coordinates are encoded using coordinate pair
      Abscissae (x-coordinates) are specified to the nearest 0.000016
      Ordinates (y-coordinates) are specified to the nearest 0.000016
      Planar coordinates are specified in meters

      The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
      

7. How does the data set describe geographic features?

   elm-geol.aat

   Arc attributes for coverage 'elm-geol' (Faults, depositional contacts, and rock units) (Source: This Publication)

   FNODE#

   ARC/INFO maintained attribute (Source: ARC/INFO)

   topologic calculation

   TNODE#

   ARC/INFO maintained attribute (Source: ARC/INFO)

   topologic calculation

   LPOLY#

   ARC/INFO maintained attribute (Source: ARC/INFO)

   topologic calculation

   RPOLY#

   ARC/INFO maintained attribute (Source: ARC/INFO)

   topologic calculation

   LENGTH

   length of the feature (Source: ARC/INFO)

   topologic calculation

   ELM-GEOL#

   ARC/INFO maintained attribute (Source: ARC/INFO)

   Calculated

   ELM-GEOL-ID

   ARC/INFO maintained attribute (Source: ARC/INFO)

   Calculated

   LTYPE

   Description of the type of geologic line (Source: This Publication)

   Value	Definition
   contact, approx. located	Boundary between two mapped units that has been observed but the location is not precise
   contact, certain	Boundary between two mapped units that was observed, the location of which is well known and is described in Positional_Accuracy
   contact, gradational	Boundary between two mapped units that is transitional over an area.
   fault, approx. located	Structural boundary between mapped units or structural discontinuity within a mapped unit that has experienced relative offset. Locational accuracy is approximate, and described in Positional_Accuracy.
   fault, approx. located, queried	Structural boundary between mapped units or structural discontinuity within a mapped unit that has experienced relative offset. The existence is inferred from structural, stratographic, of lineament relations. Locational accuracy is approximate, and described in Positional_Accuracy.
   fault, certain	Structural boundary between mapped units or structural discontinuity within a mapped unit that has experienced relative offset. Locational accuracy is well located, and described in Positional_Accuracy.
   fault, concealed	Structural boundary between mapped units or structural discontinuity within a mapped unit that has experienced relative offset. The fault is obscured by overlying map units, so it is not well-located as described in Positional_Accuracy, but is constrained to within about 120 meters on the ground.
   fault, concealed, queried	Structural boundary between mapped units or structural discontinuity within a mapped unit that has experienced relative offset. The fault is obscured by overlying map units, so it is not well-located as described in Positional_Accuracy, but is constrained to within about 150 meters on the ground. Existence of the fault is inferred from lineaments or structural relations elsewhere.
   map boundary, certain	Edge of mapped area, used to bound polygons at the edge of the map database. Locational confidence is described in Positional_Accuracy
   scratch boundary	An arbitrary line usually with no geologic significance, but sometimes used to divide polygons with the same rock type, but divided by a separate attribute

   elm-geol.pat

   Polygon attributes for coverage 'elm-geol' (Faults, depositional contacts, and rock units) (Source: This Publication)

   AREA

   Area of the feature in map units (Source: ARC/INFO)

   topologic calculation

   PERIMETER

   Perimeter of the feature in map units (Source: ARC/INFO)

   topologic calculation

   ELM-GEOL#

   ARC/INFO maintained attribute (Source: ARC/INFO)

   Calculated

   ELM-GEOL-ID

   ARC/INFO maintained attribute (Source: ARC/INFO)

   Calculated

   PTYPE

   Geologic unit attribute (Source: This Publication)

   Geologic map unit labels are described in the accompanying geologic report, or in the map sheet.

   ITEMID

   Provides a common field to which other tabular data (ELM-GEOL.PID) can be used in a relational database (Source: This Publication)

   Range of values
   Minimum:	1
   Maximum:	967

   elm-str.aat

   Arc features in coverage 'elm-str' (Geologic structure layer - strike and dips, fold axis, etc) (Source: This Publication)

   elm-str.pat

   Point features in coverage 'elm-str' (Geologic structure layer - strike and dips, fold axis, etc) (Source: This Publication)

   elm-spr.pat

   Point Features in the coverage 'elm-spr' (Location of spring mound deposits) (Source: This Publication)

   elm-kar.pat

   Point Features in the coverage 'elm-kar' (locations of dated samples) (Source: This Publication)

   elm-srcs

   An index of previous mapping (Source: This Publication)

   elm-strat

   Mapping strategies used by the authors of this report (Source: This Publication)

   elm-topo

   Vector representation of a topographic map for the mapped area (Source: This Publication)

   elm-obs

   Point Features in the coverage 'elm-obs' (locations of field observations) (Source: This Publication)

   Entity_and_Attribute_Overview:

   This database consists of eight ARC/INFO format data sets (coverages), each of which is considered a layer comprising a geologic map. These layers are: a geology layer (elm-geol), a geologic structure layer (elm-str), locations of spring mounds (elm-spr), locations of dated samples (elm-kar), areas of previous mapping (elm-srcs), areas of mapping strategies (elm-strat), locations of field observations (elm-obs), and a vector representation of a topographic map (elm-topo).

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   The primary layer is the geology layer (elm-geol), which consists of both polygon features and arc features that describes map units (polygons), and depositional contacts, faults (which may or may not be polygon bounding features) and map boundaries.

   Map units (polygons) are described in the polygon attribute table (elm-geol.pat). The identities of the map units are recorded in the PTYPE field by map label (i.e. Qvof). For a description of the map units, consult the PostScript or PDF explanation pamphlets in this report. Areal features in the geology layer (ELM-GEOL) that require attributes other than a map unit, are given unique identification numbers in the ITEMID field. ITEMID provides a common field to which other tabular data (ELM-GEOL.PID) can be used in a relational database.

   Geologic lines (arcs) are recorded as strings of vectors and are described in the arc attribute table (elm-geol.aat). They define the boundaries of the map units, the faults, and the map boundaries. These distinctions, including the geologic identities of the unit boundaries, are recorded in the LTYPE field. Attributes for geologic lines generally follow a scheme of the type of geologic line (i.e. fault), followed by a locational and/or scientific modifier (i.e. approx. located or queried).

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   The geologic structure layer (elm-str) consists of arc and point features that describe geologic structures such as strike and dip of beds, and fold axis. Arc features are described in the arc attribute table (elm-str.aat), and in this report only describe linear representations of fold axis and lineaments interpreted from air photography. The type of linear structural feature is distinguished in the LTYPE field. Point features are described in the point attribute table (elm-str.pat) and are used to represent locations of structural measurements such as strike and dip, and foliation. The type of structural measurement of points is attributed in the PTTYPE field, and the measurements taken at that location are attributed in the STRIKE and DIP fields.

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   Point features representing location of spring mound deposits (elm-spr) are described in the point attribute table (elm-spr.pat). Attributes of features in this dataset are recorded in the PTTYPE field.

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   Point features representing location of Potassium/Argon (K/Ar) dated samples (elm-kar) are described in the point attribute table (elm-kar.pat). Attributes of features in this dataset are recorded in the PTTYPE field.

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   An index of previous mapping (ELM-SRCS) consists of four ARC/INFO regions: PREVMAP1, PREVMAP2, PREVMAP3, and PREVMAP4. ARC/INFO regions allow polygonal information to be stored in a way that areas, or regions, can be overlapping, or non-contiguous in nature. Attribute information for regions is stored in tables that have the name of the coverage Polygon Attribute Table (PAT), followed by the name of a region (i.e. elm-srcs.patprevmap1). Regions may have different table definitions (items) than the base Polygon Attribute Table, and regions within the same coverage may have different table definitions (items). Each region has identical table definitions, consisting of the following items: AUTHORS, YEAR, TITLE, PUBLICATION, and SCALE. The Polygon Attribute Table (ELM-SRCS.PAT) has no attributes with the exception of the default ARC/INFO attributes. For complete bibliographic references, see appendix 1 in the geologic discussion of this report.

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   Mapping strategies used by the authors of this report (ELM-STRAT) are represented as polygons. The mapping strategies are described in the Polygon Attribute Table (ELM-STRAT.PAT) for this coverage. The mapping strategies are described in the following items: FIELDID, GEOLOGIST, and METHODS.

   Entity_and_Attribute_Detail_Citation: This Publication

   Entity_and_Attribute_Overview:

   Point features representing location of field observations made by the authors of this report. Attributes of features in this dataset are recorded in the PTTYPE field in the point attribute table (elm-obs.pat). There is only one attribute in this field: Field Observation

   Entity_and_Attribute_Detail_Citation: This Publication

1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
   • Miller, David M.
   • Bedford, David R.

2. Who also contributed to the data set?

   U.S. Geological Survey

3. To whom should users address questions about the data?

   David M. Miller
   U.S. Geological Survey
   Geologist
   345 Middlefield Rd
   MS 975
   Menlo Park, CA 94025
   USA
   

   (650) 329-4923 (voice)
   (650) 329-4936 (FAX)
   dmiller@usgs.gov
   

This digital geologic map database, intended for use at 1:24,000-scale, describes and portrays the rock units and surficial deposits of the El Mirage Lake area. It was prepared as part of a water-resource assessments of the area, describing and interpreting surface geology that provides information to help understand distribution and extent of deeper groundwater-bearing units. Map data were assembled as a digital database using ARC/INFO to enable wider applications than traditional paper-product geologic maps and to provide for efficient integration with other digital data bases prepared by the U.S. Geological Survey's Southern California Areal Mapping Project (<http://geology.wr.usgs.gov/wgmt/scamp>), other federal and state agencies, and the Mojave Water Agency.

1. Where did the data come from?

   Dibblee (1960) (source 1 of 4)

   Dibble, T.W., 1960, Preliminary geologic map of the Shadow Mountains quadrangle, Los Angeles and San Bernardino Counties, California: U.S. Geological Survey Mineral Investigations Field Studies Map MF-227.

   Type_of_Source_Media: paper

   Source_Scale_Denominator: 62500

   Source_Contribution:

   Distinguished a few surficial geologic units, four granitoid units, and several metamorphic rock units. Mapped the most evident faults, as well as folds in metamorphic rocks.

   Troxel and Gunderson (1970) (source 2 of 4)

   Troxel, B.W. Gunderson, J.N., 1970, Geology of the Shadow Mountains and northern part of the Shadow Mountains SE quadrangles, western San Bernardino County, California: California Division of Mines and Geology Preliminary Report 12.

   Type_of_Source_Media: paper

   Source_Scale_Denominator: 24000

   Source_Contribution:

   Distinguished a few surficial geologic units, a few granitoid units, and several metamorphic rock units. Mapped granitoid and metamorphic rock units in detail, as well as faults and folds in metamorphic rocks. Mapped lineaments and faults in pediments.

   Ponti and Burke (1980) (source 3 of 4)

   Ponti, D.J. Burke, D.B, 1980, Map showing Quaternary geology of the eastern Antelope Valley and vicinity, California: U.S. Geological Survey Open File Report OFR80-1064.

   Type_of_Source_Media: paper

   Source_Scale_Denominator: 62500

   Source_Contribution:

   Mapped a wide range of surficial geology with a focus on areas with active faulting. Mapped several previously unrecognized faults in the El Mirage Lake area but did not break out many surficial geology units in this area.

   Martin (1992) (source 4 of 4)

   Martin, M.W., 1992, Stratigraphic and structural evolution of the Shadow Mountains, western Mojave Desert, California: Implications for the tectonic development of the central and western Mojave Desert.

   Other_Citation_Details: Unpublished Ph.D. dissertation, University of Kansas, 196 p

   Type_of_Source_Media: paper

   Source_Scale_Denominator: 12000

   Source_Contribution:

   Conducted very detailed (1:12,000) mapping of bedrock in Shadow Mountains but none in pediments. Distinguished several map units in metamorphic rocks and deduced sedimentary, metamorphic, and structural history.

2. What changes have been made?

   Date: 1999 (change 1 of 1)

   ARC/INFO version 7.2.1, 8.0.1, ArcView version 3.1

1. How well have the observations been checked?

2. How accurate are the geographic locations?

   Accuracy of line locations is carried in the database and displayed by different line symbols (solid vs. dashed lines) in the cartographic display. For the purpose of this database, solid lines represent contacts and faults located with an accuracy greater than 10 m and commonly greater than 5 m. Dashed lines represent two kinds of less certainly located features, each distinguished in the database: 1) contacts and faults located with an accuracy of 10 to 15 m, 2) contacts that represent gradational boundaries between adjacent units. Gradational contacts represent interleaving of sediments and smooth gradations in characteristics such as percentage of eolian sand. In general, these gradations take place over distances of 50 to 150 m. Lineaments and fold axes are lines whose positions do not affect location of polygons; they are located with an accuracy of 25 m.

3. How accurate are the heights or depths?

4. Where are the gaps in the data? What is missing?

   This report is intended to completely describe the surficial and bedrock materials of the map area at a scale of 1:24000.

5. How consistent are the relationships among the observations, including topology?

   Polygon and chain-node topology present. Geologic lines attributed as a 'contact' do not separate geologic map units of the same type.

Are there legal restrictions on access or use of the data?

Access_Constraints: None

Use_Constraints:

Acknowledgement of the U.S. Geological Survey, Southern California Areal Mapping Project, Mojave Water Agency, and California Division of Mines and Geology would be appreciated in products derived from this dataset

1. Who distributes the data set? (Distributor 1 of 1)

   U.S. Geological Survey
   c/o El Mirage Lake California Database
   Database coordinator
   345 Middlefield Road, MS 975
   Menlo Park, CA 94025
   USA
   

   (650) 329-2923 (voice)
   

2. What's the catalog number I need to order this data set?

   All files for this report can be accessed via the World Wide Web at: <http://wrgis.wr.usgs.gov/open-file/of00-222> or through File Transfer Protocol (FTP) at <ftp://wrgis.wr.usgs.gov/pub/open-file/of00-222/>

3. What legal disclaimers am I supposed to read?

   This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

   This database, identified as "Geologic Map Database of the El Mirage Lake Area, San Bernardino and Los Angeles Counties, California," has been approved for release and publication by the Director of the USGS. Although this database has been subjected to rigorous review and is substantially complete, the USGS reserves the right to revise the data pursuant to further analysis and review. Furthermore, it is released on condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.

4. How can I download or order the data?
   • Availability in digital form:

     Data format:	ARC/INFO export files, explanatory materials, and printable maps for the digital database can be downloaded at the specified URL in format ARCE (version 8.0)
     Network links:	<http://geopubs.wr.usgs.gov/open-file/of00-222/> <ftp://geopubs.wr.usgs.gov/pub/open-file/of00-222/>

   • Cost to order the data: None

5. Is there some other way to get the data?

   Database files, PostScript plotfiles, and related files can be obtained by sending a tape or CDR (Recordable CD-ROM) with request and return address to:

   El Mirage Lake, California Database c/o Database Coordinator U.S. Geological Survey 345 Middlefield Road, M/S 975 Menlo Park, CA 94025

   Do not omit any part of this address!

   The compressed tar file will be returned on the tape or CD-ROM. The acceptable tape type is: 2.3 or 5.0 GB, 8 mm Exabyte tape.

Dates:

Last modified: 23-Mar-2000

Metadata author:

David R. Bedford
U.S. Geological Survey
Geologist
345 Middlefield Rd
MS 975
Menlo Park, CA 94025
USA

650-329-4924 (voice)
650-329-4936 (FAX)
dbedford@usgs.gov

Metadata standard:

FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)

Metadata extensions used:

• <http://www.esri.com/metadata/esriprof80.html>