Miller, David M. Bedford, David R. 2000 1.0 vector digital data U.S. Geological Survey Open File Report 00-222 Menlo Park, CA U.S. Geological Survey http://wrgis.wr.usgs.gov/open-file/of00-222 http://geopubs.wr.usgs.gov/open-file/of00-222 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). 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. 1999 ground condition Complete As needed -117.690702 -117.501459 34.735409 34.499069 None Mojave El Mirage Geology geologic map geologic database None Mojave Desert San Bernardino County Los Angeles County Southern California El Mirage Nash Hill Shadow Mountains Adobe Mountain None 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 David M. Miller U.S. Geological Survey Geologist mailing and physical address

345 Middlefield Rd MS 975

Menlo Park CA 94025 USA (650) 329-4923 (650) 329-4936 dmiller@usgs.gov elm_browse.jpg Thumbnail JPEG U.S. Geological Survey Windows NT Version 4.0 (Build 1381) Service Pack 5; ESRI ArcInfo 8.0.297 Polygon and chain-node topology present. Geologic lines attributed as a 'contact' do not separate geologic map units of the same type. This report is intended to completely describe the surficial and bedrock materials of the map area at a scale of 1:24000. 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. Dibble, T.W. 1960 U.S. Geological Survey Mineral Investigations Field Studies Map MF-227 62500 paper 1960 publication date Dibblee (1960) 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, B.W. Gunderson, J.N. 1970 California Division of Mines and Geology Preliminary Report 12 24000 paper 1970 publication date Troxel and Gunderson (1970) 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, D.J. Burke, D.B 1980 U.S. Geological Survey Open File Report OFR80-1064 62500 paper 1980 publication date Ponti and Burke (1980) 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, M.W. 1992 Unpublished Ph.D. dissertation, University of Kansas, 196 p 12000 paper 1992 publication date Martin (1992) 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. ARC/INFO version 7.2.1, 8.0.1, ArcView version 3.1 1999 Vector Complete chain 2651 Entity point 955 GT-polygon composed of chains 955 Point 49 Universal Transverse Mercator 11 0.9996 117.0 0.0 0 0 coordinate pair 0.000016 0.000016 meters North American Datum of 1983 Geodetic Reference System 80 6378137.000000 298.257222 elm-geol.aat Arc attributes for coverage 'elm-geol' (Faults, depositional contacts, and rock units) This Publication FNODE# ARC/INFO maintained attribute ARC/INFO topologic calculation TNODE# ARC/INFO maintained attribute ARC/INFO topologic calculation LPOLY# ARC/INFO maintained attribute ARC/INFO topologic calculation RPOLY# ARC/INFO maintained attribute ARC/INFO topologic calculation LENGTH length of the feature ARC/INFO topologic calculation ELM-GEOL# ARC/INFO maintained attribute ARC/INFO Calculated ELM-GEOL-ID ARC/INFO maintained attribute ARC/INFO Calculated LTYPE Description of the type of geologic line This Publication contact, approx. located Boundary between two mapped units that has been observed but the location is not precise Author contact, certain Boundary between two mapped units that was observed, the location of which is well known and is described in Positional_Accuracy Author contact, gradational Boundary between two mapped units that is transitional over an area. Author 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. Author 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. Author 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. Author 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. Author 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. Author 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 Author 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 Author elm-geol.pat Polygon attributes for coverage 'elm-geol' (Faults, depositional contacts, and rock units) This Publication AREA Area of the feature in map units ARC/INFO topologic calculation PERIMETER Perimeter of the feature in map units ARC/INFO topologic calculation ELM-GEOL# ARC/INFO maintained attribute ARC/INFO Calculated ELM-GEOL-ID ARC/INFO maintained attribute ARC/INFO Calculated PTYPE Geologic unit attribute 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 This Publication 1 967 elm-str.aat Arc features in coverage 'elm-str' (Geologic structure layer - strike and dips, fold axis, etc) This Publication elm-str.pat Point features in coverage 'elm-str' (Geologic structure layer - strike and dips, fold axis, etc) This Publication elm-spr.pat Point Features in the coverage 'elm-spr' (Location of spring mound deposits) This Publication elm-kar.pat Point Features in the coverage 'elm-kar' (locations of dated samples) This Publication elm-srcs An index of previous mapping This Publication elm-strat Mapping strategies used by the authors of this report This Publication elm-topo Vector representation of a topographic map for the mapped area This Publication elm-obs Point Features in the coverage 'elm-obs' (locations of field observations) This Publication 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). This Publication 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). This Publication 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. This Publication 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. This Publication 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. This Publication 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. This Publication 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. This Publication 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 This Publication U.S. Geological Survey El Mirage Lake California Database Database coordinator mailing address

345 Middlefield Road, MS 975

Menlo Park CA 94025 USA (650) 329-2923 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/ 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. ARCE 8.0 ARC/INFO export files, explanatory materials, and printable maps for the digital database can be downloaded at the specified URL no compression applied http://geopubs.wr.usgs.gov/open-file/of00-222/ ftp://geopubs.wr.usgs.gov/pub/open-file/of00-222/ None 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. 20000323 David R. Bedford U.S. Geological Survey Geologist mailing and physical address

345 Middlefield Rd MS 975

Menlo Park CA 94025 USA 650-329-4924 650-329-4936 dbedford@usgs.gov FGDC Content Standards for Digital Geospatial Metadata FGDC-STD-001-1998 local time http://www.esri.com/metadata/esriprof80.html ESRI Metadata Profile