Open-File Report 02-491
The quadrangle is underlain by a basement terrane comprising Proterozoic metamorphic rocks, Mesozoic plutonic rocks, and Mesozoic and Mesozoic and (or) Cenozoic hypabyssal dikes. The basement terrane is capped by a widespread Tertiary erosion surface preserved in remnants in the Hexie and Pinto Mountains and buried beneath Cenozoic deposits in Pinto Basin. Locally, a cover of Miocene sedimentary deposits and basalt overlie the erosion surface. Quaternary and (or) Tertiary lacustrine deposits crop out in the center of Pinto Basin and interfinger laterally with sandstone, conglomerate, and debris flows originating in the Pinto and Hexie Mountains. A sequence of at least three Quaternary pediments is planed into the north piedmonts of the Hexie and Eagle Mountains, each in turn overlain by successively younger residual and alluvial, surficial deposits. The Tertiary erosion surface is deformed and broken by north-northwest-trending, high-angle, dip-slip faults in the Pinto and Eagle Mountains and an east-west trending system of high-angle dip- and left-slip faults along the range fronts facing Pinto Basin. In and around the Pinto Mountain quadrangle, faults of the north-northwest-trending set displace Miocene sedimentary rocks and basalt deposited on the Tertiary erosion surface and some of the faults may offset Pliocene and (or) Pleistocene deposits that accumulated on the oldest pediment. Faults of this system appear to be overlain by Pleistocene deposits that accumulated on younger pediments. East-west trending faults are younger than and perhaps in part coeval with faults of the northwest-trending set.
The Pinto Mountain database was created using ARCVIEW and ARC/INFO, which are geographical information system (GIS) software products of Envronmental Systems Research Institute (ESRI). The database comprises eight coverages: (1) a geologic layer showing the distribution of geologic contacts and units; (2) a structural layer showing the distribution of faults (arcs) and fault ornamentation data (points); (3) a layer showing the distribution of dikes (arcs); structural point data layers showing (4) bedding attitudes, (5) foliation attitudes, (6) lineations, (7) minor fold axes; and (8) cartographic map elements, including unit label leaders and geologic unit annotation. The dataset also includes a scanned topographic base at a scale of 1:24,000. Within the database coverages, geologic contacts , faults, and dikes are represented as lines (arcs and routes), geologic units as areas (polygons and regions), and site-specific data as points. Polygon, region, arc, route, and point attribute tables uniquely identify each geologic datum and link it to descriptive tables that provide more detailed geologic information.
The digital database is accompanied by two derivative maps: (1) A portable document file (.pdf) containing a navigable graphic of the geologic map on a 1:24,000 topographic base and (2) a PostScript graphic-file containing the geologic map on a 1:24,000 topographic base. Each of these map products is accompanied by a marginal explanation consisting of a Description of Map Units (DMU), a Correlation of Map Units (CMU), and a key to point and line symbols. The database is further accompanied by three document files: (1) a readme that lists the contents of the database and describes how to access it, (2) a pamphlet file that describes the geology of the quadrangle, and (3) this metadata file.
The digital geologic map database for the Pinto Mountain quadrangle has been created as a general-purpose data set that is applicable to land-related investigations in the earth and biological sciences. Along with geologic map databases in preparation for adjoining quadrangles, the Pinto Mountain database has been generated to further our understanding of bedrock and surficial processes at work in the region and to document evidence for seismotectonic activity in the eastern Transverse Ranges. The database is designed to serve as a base layer suitable for ecosystem and mineral resource assessment and for building a hydrogeologic framework for the Pinto Basin.
Within the geologic map database, map units are identified by standard geologic map criteria such as formation-name, age, and lithology. The authors have attempted to adhere to the stratigraphic nomenclature of the U.S. Geological Survey and the North American Stratigraphic Code, but the database has not received a formal editorial review of geologic names.
Geologic map unit labels are present in three forms in the database. First, map unit labels are entered into the database through various items in the polygon attribute table, dike arc attribute table, and region attribute tables. Geologic map units are tabulated in items such as UNIT_LABEL and POLY_LABEL, where they are identified by plain-text unit labels (e.g., Qyam1, Prjgg). These labels do not show subscript offsets and do not contain conventional stratigraphic age symbols, i.e., Proterozoic appears as 'Pr'. Second, for the purpose of plotting the map, the item PLOT_LABEL, located in the polygon attribute and map display tables, identifies the unit label as it is plotted by Arc/Info (e.g., Qyam1, <jgg), again without subscripts and containing substitute characters for conventional stratigraphic age symbols: Proterozoic appears as '<'. The substitute character in PLOT_LABEL invokes its corresponding symbol from the GeoAge font group to generate map plots that display conventional stratigraphic symbols. Third, annotation labels for map units, derived from the item PLOT_LABEL but showing subscripts (e.g., Qyam1), are stored in the annotation subclass anno.geo of the arc coverage pmtn_carto/.
Content. This database, identified as "Geologic map and digital database of the Pinto Mountain 7.5 minute quadrangle, Riverside County, California" has been approved for release and publication by the Director of the U.S. Geological Survey. 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 the condition that neither the USGS nor the United States Government may be held responsible for any damages resulting from its authorized or unauthorized use. This database 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.
Faults. The Pinto Mountain database is sufficiently detailed to identify and characterize many actual and potential geologic hazards represented by faults, but it is not sufficiently detailed for site-specific determinations or evaluations of these features. Faults shown do not take the place of fault-rupture hazard zones designated by the California State Geologist (see, for example, Hart, 1988; Hart and Bryant, 1997).
Hart, E. W., 1988, Fault-rupture zones in California; Alquist-Priolo Special Studies Zones Act of 1972 with index to special studies zones maps (revised, 1988): California Division of Mines and Geology Special Publication 42.
Hart, E. W., and Bryant, W.A., 1997, Fault-rupture zones in California; Alquist-Priolo Special Studies Zones Act of 1972 with index to special studies zones maps (revised, 1997): California Division of Mines and Geology Special Publication 42.
This database was prepared in the GIS laboratory at the Spokane Field Office of the USGS in Spokane, Washington. The facility is maintained primarily by the Mineral Resource Surveys Program and supported in part by the National Geologic Mapping Program.
Technical review by Fred K. Miller has led to significant improvements in the database and in the map plot file. Digital review by Rachel Hauser Alvarez has allowed us to further improve the digital database.
The areal extent of the map is represented digitally by an appropriately projected (Polyconic projection), mathematically generated box. Consequently, polygons intersecting the lines that comprise the map boundary are closed by that boundary. Polygons internal to the map boundary are completely enclosed by line segments which are themselves a set of sequentially numbered coordinate pairs. Point data are represented by coordinate pairs.
Geologic lines that are not discrete (e.g., gradational or transitional contacts), are not well exposed, or cannot be located within the limits defined by the national map accuracy standard are considered to be approximately located. Linear features in the Pinto Mountain geologic map database are represented as solid, dashed, and dotted lines. Using a DOQQ base, linear features represented by solid lines are located to within 33.3 ft (10 m) or less of their position on the ground. Linear features represented as dashed or dotted lines may or may not be located to within 10 m of their position on the ground. Linear features represented by dotted lines are concealed beneath overlying mapped units.
The accuracy of point features in the Pinto Mountain database is +/-10 ft for points located on the DOQQ base, +/-33 ft for points located on a 1:24,000-scale topographic base, and +/-52 ft for points located on a 1:62,000-scale topographic base. Contacts between lithologic domains that make up surficial deposits as mapped on the DOQQs typically are readily located to within 10 m, but to make domains that can be resolved at 1:24,000 contacts are often drawn by approximating the dominant unit on a percentage basis. Interspersal of well- and approximately located segments is common among the many thousands of contacts present in the Pinto Mountain quadrangle. Given that many quadrangles are being mapped in a relatively short time interval, it was deemed too time-consuming to distinguish well-located and approximately located contacts between surficial deposits; therefore, all surficial contacts are represented as approximately located and shown with a dashed line symbol.
Powell, R.E., 1981, Geology of the crystalline basement complex, eastern Transverse Ranges, southern California: Constraints on regional tectonic interpretation [Ph.D. thesis]: Pasadena, California Institute of Technology, 441 p.
USGS, 1973, True color aerial photographs labeled GS-SE. Photographs taken along northwest-southeast oriented flight lines covering the eastern Transverse Ranges south of the Pinto Mountain fault. Lines flown at moderate to low sun-angle in October 1973; scale 1:36,000.
Powell, R.E., 1993, Balanced palinspastic reconstruction of pre-late Cenozoic paleogeology, southern California: Geologic and kinematic constraints on evolution of the San Andreas fault system, in Powell, R.E., Weldon, R.J., II, and Matti, J.C., eds., The San Andreas fault system: Displacement, palinspastic reconstruction, and geologic evolution: Geological Society of America Memoir 178, p. 1-106.
USGS, 1998, True color aerial photographs labeled J.T.N.P. Photographs taken along east-west oriented flight lines covering part of Joshua Tree National Park in Pinto Basin and parts of the Coxcomb, Pinto, Eagle, Cottonwood, Hexie, and Little San Bernardino Mountains. Lines flown at high sun-angle in May 1998; scale 1:24,000.
(1) The coverage pmtn_geo includes the following feature tables: (a) A polygon attribute table (pmtn_geo.pat) that lists labels for the geological characteristics and identifies plot labels for the rock units represented in the Postscript (.ps) and Portable Document Format (.pdf) plotfiles of the geologic maps; (b) Region subclass attribute tables that describe the geospatial distribution of rock units represented in the Postscript (.ps) and Portable Document Format (.pdf) plotfiles of the geologic maps (pmtn_geo.patrockunit), the hierarchical array of stratigraphic parents of rock units in the crystalline basement (pmtn_geo.patbasement1, pmtn_geo.patbasement2, pmtn_geo.patbasement3, pmtn_geo.patbasement4), the hierarchical array of stratigraphic parents of rock units in sedimentary and volcanic cover to the basement rocks (pmtn_geo.patcover1, pmtn_geo.patcover2), and the hierarchical array of stratigraphic parents of surficial units (pmtn_geo.patsurficial1, pmtn_geo.patsurficial2, pmtn_geo.patsurficial3, pmtn_geo.patsurficial4, pmtn_geo.patsurficial5). This hierarchy of stratigraphic units can be related in ArcInfo, ArcMap or ArcView to display or plot more generalized, derivative geologic maps than that represented in Postscript (.ps) or Portable Document Format (.pdf) files. (c) A region subclass attribute table that describes surface units (veneers) (pmtn_geo.patsurfunit). (d) A region subclass attribute table that describes mixed surface units (pmtn_geo.patmxd_surfunit). (e) A region subclass attribute table that shows those areas where unit identification is uncertain (pmtn_geo.patident). (f) An arc attribute table (pmtn_geo.aat) that describes the contacts that bound rock-unit polygons.
(2) The coverage pmtn_flt contains and displays the complete distribution of fault features within the extent of the Pinto Mountain quadrangle. Structural line ornamentation is included in this layer as point data. Faults are characterized in two route attribute tables (pmtn_flt.ratsegment and pmtn_flt.ratfault).
(3) The coverage pmtn_dk includes an arc attribute table (pmtn_dk.aat) that describes hypabyssal dikes. Dikes are planar intrusive features that intersect the Earth's surface as linear features; they are represented as lines where their surface widths are too narrow to be represented as areal features at a scale of 1:24,000.
(4) The coverages str_bedding, str_foliation, str_lineatn, and str_mnrflds include point attribute tables (<cover_name>.pat) that describe geologic structural point data, including the types and orientation of bedding, foliation, lineation, and minor fold axes, respectively. Annotation subclasses (anno.dip - planar data, anno.plunge - non-planar data) display the dip or plunge value associated with each point datum.
(5) The coverage pmtn_carto includes both geologic unit symbol annotation and an arc attribute table (pmtn_carto.aat) that displays annotation leaders. Unit symbols placed outside the perimeter of a particular polygon are identified by annotation leaders.
Concealed units listed in parentheses, surface units in <brackets>.
Map units are described in region feature subclasses.
In no event shall the USGS have any liability whatsoever for payment of any consequential, incidental, indirect, special, or tort damages of any kind, including, but not limited to, any loss of profits arising out of use of or reliance on the geographic data or arising out of delivery, installation, operation, or support by USGS.
This digital, geologic map database of the Pinto Mountain 7.5'quadrangle, and any derivative maps thereof, is not meant to be used or displayed at any map scale larger than 1:12,000 on the DOQQ base or 1:24,000 on the topograhic base.