Preliminary geologic map of the San Guillermo Mountain quadrangle, Ventura County, California, version 1.0
Originator: U.S. Geological Survey
Scott A. Minor
Preliminary geologic map of the San Guillermo Mountain quadrangle, Ventura County, California, version 1.0
Series_Name: Open-File Report
Publication_Place: Denver, Colorado
Publisher: U.S. Geological Survey
New 1:24,000-scale geologic mapping in the Cuyama 30' x 60' quadrangle, in support of the USGS Southern California Areal Mapping Project (SCAMP), is contributing to a more complete understanding of the stratigraphy, structure, and tectonic evolution of the complex junction area between the NW-striking Coast Ranges and EW-striking western Transverse Ranges. The 1:24,000-scale geologic map of the San Guillermo Mountain quadrangle is one of six contiguous 7 1/2' quadrangle geologic maps in the eastern part of the Cuyama map area being compiled for a more detailed portrayal and reevaluation of geologic structures and rock units shown on previous geologic maps of the area (e.g., Dibblee, 1979). The following observations and interpretations are based on the new San Guillermo Mountain geologic compilation:
(1) The new geologic mapping in the northern part of the San Guillermo Mountain quadrangle allows for reinterpretation of fault architecture that bears on potential seismic hazards of the region. Previous mapping had depicted the eastern Big Pine fault (BPF) as a northeast-striking, sinistral strike-slip fault that extends for 30 km northeast of the Cuyama River to its intersection with the San Andreas fault (SAF). In contrast the new mapping indicates that the eastern BPF is a thrust fault that curves from a northeast strike to an east strike, where it is continuous with the San Guillermo thrust fault, and dies out further east about 15 km south of the SAF. This redefined segment of the BPF is a south-dipping, north-directed thrust, with dominantly dip slip components (rakes > 60 deg.), that places Middle Eocene marine rocks (Juncal and Matilija Formations) over Miocene through Pliocene(?) nonmarine rocks (Caliente, Quatal, and Morales Formations). Although a broad northeast-striking fault zone, exhibiting predominantly sinistral components of slip (rakes < 45 deg.), extends to the SAF as previously mapped, the fault zone does not connect to the southwest with the BPF but instead curves into a southwest-directed thrust fault system a short distance north of the BPF. Oligocene to Pliocene(?) nonmarine sedimentary and volcanic rocks of the Plush Ranch, Caliente, and Morales(?) Formations are folded on both sides of this fault zone (informally named the Lockwood Valley fault zone [LVFZ] on the map). South-southeast of the LVFZ overturned folds have southward vergence. Several moderate-displacement (< 50 m), mainly northwest-dipping thrust and reverse faults, exhibiting mostly sinistral-oblique slip, flank and strike parallel to the overturned folds. The fold vergence and thrust direction associated with the LVFZ is opposite to that of the redefined BPF, providing further evidence that the two faults are distinct structures. These revised fault interpretations bring into question earlier estimates of net sinistral strike-slip displacement of as much as 13 km along the originally defined eastern BPF, which assumed structural connection with the LVFZ. Also, despite sparse evidence for repeated Quaternary movement on the LVFZ (e.g., Dibblee, 1982), the potential for a large earthquake involving coseismic slip on both the LVFZ and the central BPF to the southwest may not be as great as once believed. (2) Several generations of Pleistocene and younger dissected alluvial terrace and fan deposits sit at various levels above modern stream channels throughout the quadrangle. These deposits give testimony to the recent uplift and related fault deformation that has occurred in the area. (3) A vast terrane of Eocene marine sedimentary rocks (Juncal and Matilija Formations and Cozy Dell Shale) exposed south of the Big Pine fault forms the southern two-thirds of the San Guillermo Mountain quadrangle. Benthic foraminifers collected from various shale intervals within the Juncal Formation indicate a Middle Eocene age (Ulatisian) for the entire formation (K. McDougall, unpub. data, 1998) and deposition at paleodepths as great as 2,000 m (i.e., lower bathal). (4) The Lockwood Clay, of probable Pliocene age, forms a thick seam of industrial-quality clay that extends westward into the quadrangle from the area where it is currently being mined in Lockwood Valley. New mapping of the Lockwood Clay in the quadrangle indicates that, although it extends across the northern part of the quadrangle, it locally pinches where it rests unconformably on rocks of the Caliente Formation. The distribution of this clay is important not only because of its economic importance, but also due to its susceptibility to landsliding.
To update and reinterpret earlier geologic mapping, and to achieve a uniform regional geologic database.
Map political location: Ventura County, California Compilation scale: 1:24,000 Geology mapped in 1996 through 1998. Compilation completed October, 1998. Review and revision completed December, 1998. Archive files prepared April, 1999.
Currentness_Reference: publication date
Irregular. Mapping is continuing in adjacent quadrangles and a more complete final map of this area may eventually be produced.
Theme_Keyword_Thesaurus: AGI Glossery of Geology
Theme_Keyword: Geologic map
Theme_Keyword: Eocene marine sedimentary rocks
Theme_Keyword: Oligocene-Pliocene(?) terrigenous sedimentary rocks
Theme_Keyword: Quaternary surficial deposits
Theme_Keyword: transpressional faults and folds
Big Pine fault
none. Acknowledgment of the U.S. Geological Survey would be appreciated in products derived from these data.
U.S. Forest Service. California Department of Conservation, Division of Mines and Geology.
Data was entered and checked by the geologist who made the observations.
Map elements were visually checked by the author for overshoots, undershoots, duplicate features, and other errors. The report is preliminary and has not been thoroughly reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. The map was reviewed by another geologist for consistency with basic geologic principles and general conformity to USGS mapping standards.
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards and stratigraphic nomenclature. Data is complete: no features were eliminated or generalized. Unit properties are described in the text explanation. A digital base map coverage is not included but is available separately.
Lines were primarily mapped by photointerpretation of 1:24,000-scale color aerial photographs. Lines were digitized from the annotated aerial photographs by inspection using rectified and georeferenced digital orthophoto quarter quadrangles (DOQQ's) with ground resolution of 1 meter. Most digitized positions on the map are estimated to have about 20 m horizontal accuracy. Additional point observations were added using positions determined by a Rockwell PLGR-96 GPS unit with horizontal accuracy of about 10 meters. There is no elevation data in the database.
The sanguill geologic database was compiled using the GSMCAD public domain program (USGS Open-File Report 96-007; program availible at <http://ncgmp.cr.usgs.gov/ncgmp/gsmcad>). It was exported to ARC/INFO using the GSMCAD export function to create ARC generate ASCII files and the gsmarc.aml program in ARC was used to convert the ASCII files to ARC coverages and build polygons.
- Direct_Spatial_Reference_Method: Vector
- Map_Projection_Name: Lambert Conformal Conic
- Standard_Parallel: 35.46666666667
- Standard_Parallel: 34.033333333333
- Longitude_of_Central_Meridian: -118.0
- Latitude_of_Projection_Origin: 0.0
- False_Easting: 0.000
- False_Northing: 0.000
- Planar_Coordinate_Encoding_Method: coordinate pair
- Abscissa_Resolution: 0.001
- Ordinate_Resolution: 0.001
- Planar_Distance_Units: METERS
- Horizontal_Datum_Name: North American Datum of 1927
- Ellipsoid_Name: Clarke 1866
- Semi-major_Axis: 6378206.4
- Denominator_of_Flattening_Ratio: 294.98
- The data is supplied in ARC/INFO export format.
- DATABASE STRUCTURE - ARC/INFO ====================================
- The database of the map consists of four coverages (root name = sgm), including corresponding INFO files:
- sgmpoly coverage: Contains all contact lines and labelpoints for each polygon. In the coverage's sgmpoly.aat INFO file the CODE item provides a numeric code that specifies the geologic identity and positional quality of each contact line (e.g., fault, approximately located), and the P1 and P2 items are relic cartographic parameters from the GSMCAD compilation program. The sgmpoly.aat CODE values are defined below. In the sgmpoly.pat INFO file the CODE and P2 items are relic cartographic parameters from the GSMCAD program, the P1 item provides a numeric code that specifies the polygon's map unit identity, the TEXT item indicates the map unit label for each polygon, and the SYMBOL item defines the polygon color as chosen from the color524.shd shadeset (included in bundled file archive). The sgmpoly.pat P1 and TEXT items are listed below.
- sgmline coverage: Contains faults, fold axis, and other non-contact lines. Faults that are contacts also appear in the sgmpoly coverage. In the sgmline.aat INFO file the CODE item provides a numeric code that specifies the geologic identity and positional quality for each type of line, the P1 and P2 items are relic cartographic parameters from the GSMCAD program, and the TEXT item describes the geologic identity, positional quality, and, in some cases, additional aspects of each line. The sgmline.aat CODE and TEXT items are listed below.
- sgmpoint coverage: Contains points recording site-specific observations and measurements, such as strike and dip of bedding. In the sgmpoint.pat INFO file the CODE item provides a numeric code that specifies the type of point observation, the P1 and P2 items indicate the associated strike azimuth (or trend) and dip (or plunge), respectively, and the TEXT item describes the type of point observation. (In the case of bedding attiudes the P1 strike azimuths are always 90 deg. counterclockwise from the associated dip directions.) The sgmpoint.pat CODE and TEXT items are listed below.
- sgmdec coverage: Contains points used for cartographically decorating lines, such as "ball-and-bar" fault symbols, as well as a repeat of points in the sgmpoint coverage recording site-specific observations and measurements. Such point data provide additional qualitative information mainly for line features representing faults and folds, such as sense of fault displacement or fold type. In the INFO file sgmdec.pat the CODE item defines a numeric code for each type of point decoration and the P1 and P2 items indicate the orientation (or strike azimuth) and, where appropriate, dip (or plunge) value associated with each point symbol. The sgmdec.pat CODE items are listed below.
- Auxiliary files:
- color524.shd: This shadeset file defines the rgb values of colors assigned to polygons in the sgmpoly coverage (see SYMBOL item). sgm24k.pdf: A file for viewing and printing a graphics version of the map and accessory elements using Adobe Acrobat viewing software (version 4.0). (Adobe Acrobat 4.0 viewing software is free and can be downloaded at the following URL: <http://www.adobe.com/products/acrobat/readstep.html>) Accessory map elements displayed in this graphics file are: (1) geologic cross section A-A", (2) geologic cross section B-B', (3) correlation of map units diagram, (4) list of map unit symbols and names, and (5) explanation of map symbols. sgmexpl.pdf: A detailed textual description of geologic map units and a brief discussion of deposits, structure, and geologic history of the map area. Can be displayed using the Adobe Acrobat viewing software (version 4.0).
- P1 | GEOLOGIC MAP UNIT LABELS 1 | Qa 2 | Qac 4 | Qma 5 | Qmac 11 | Qoa 12 | Qoac 13 | Qls 14 | Qols 15 | Qbd 18 | Tm 20 | Tqb 21 | Tqc 23 | Tlc 24 | Tc 25 | Tcau 26 | Tcv 28 | Tcl 29 | Tcg 30 | Tcc 32 | Tcal 33 | Tcp 36 | Tjs 37 | Tjsh 38 | Tjm 40 | Tjc 42 | Tps 43 | Tpl 44 | Tpb 47 | Tpbn 57 | Tcsh (sheared Tc) 58 | Tpsh (sheared Tp) 59 | Tma 60 | Tmam 61 | Tcd 62 | Tcds 63 | Qya
- DEFINITION OF CODES IN THE DATABASE COVERAGES (CODES AND TEXT LISTED IN THE .AAT AND .PAT FILES) CODE | TEXT (DEFINITION) 1 | contact; certain 3 | contact; approximately located 4 | contact; inferred 8 | custom contact A 10 | fault; certain 11 | fault; concealed 13 | fault; approximately located 14 | fault; inferred 40 | thrust fault; certain; upthrown on right side 41 | thrust fault; concealed; upthrown on right side 44 | thrust fault; approximate location; upthrown on right side 45 | thrust fault; inferred; upthrown on right side 70 | anticline axis; certain 71 | anticline axis; concealed 72 | anticline axis; inferred 74 | syncline axis; certain 75 | syncline axis; concealed 76 | syncline axis; inferred 80 | dike 83 | marker bed A 86 | conglomeratic marker bed 92 | landslide scarp; slide block on right 94 | landslide scarp; slide block on right 97 | scratch boundary 98 | cross section profile line 99 | map boundary 201 | bedding attitude (P1=strike azimuth 90 deg.CCW from dip direction, P2=dip angle) 204 | anticline symbol (P1=orientation azimuth) 205 | syncline symbol (P1=orientation azimuth) 207 | ball & bar symbol (P1=orientation azimuth) 208 | fault attitude (P1=strike azimuth, P2=dip angle) 209 | left lateral symbol (P1=orientation azimuth) 210 | right lateral symbol (P1=orientation azimuth) 219 | OT bedding attitude (P1=strike azimuth 90 deg.CCW from dip direction, P2=dip angle) 220 | approximate bedding attitude (P1=strike azimuth 90 deg.CCW from dip direction, P2=dip angle) 227 | OT anticline symbol (P1=orientation azimuth) 228 | OT syncline symbol (P1=orientation azimuth) 241 | fold axis plunge symbol (P1=orientation azimuth) 268 | fault slickenside lineation (P1=trend, P2=plunge) 299 | bedding attitude from previous mapping (P1=strike azimuth 90 deg.CCW from dip direction, P2=dip angle) 362 | Flat bedding 376 | Drill hole 410 | Shear zone fill symbol 500 | Unit labels text & tag 501 | Hidden unit tags 502 | rock text 510 | ordinary text 701 | Splined text
U.S. Geological Survey, National Cooperative Geologic Mapping Team
Address_Type: mailing address
Address: Scott A. Minor
Address: U.S. Geological Survey
Address: MS 913, Box 25046 DFC
Although this digital spatial data has been subjected to rigorous review and is substantially complete, it is released on the condition that neither the USGS nor the United States Government may be held liable for any damages resulting from its authorized or unauthorized use.
Format_Name: ARC/INFO export
File_Decompression_Technique: GZIP self-extracting archive, Unix or Windows versions
- Metadata_Date: 19990401
- Metadata_Review_Date: 19990421
- Contact_Person: Scott A. Minor
- U.S. Geological Survey, National Cooperative Geologic Mapping Team
- Address_Type: mailing address
- Address: U.S. Geological Survey
- Address: MS 913, Box 25046 DFC
- City: Lakewood
- State_or_Province: CO
- Postal_Code: 80225-0046
- Contact_Voice_Telephone: 303-236-0303
- Contact_Voice_Telephone: 303-236-7880
- Metadata_Standard_Name: FGDC Content Standards for Digital Geospatial Metadata
Generated by mp version 2.3.6 on Fri Apr 23 15:35:33 1999