Rocks of the four basement rock assemblages are divisible into an older suite of Late Cretaceous and older rocks and a younger suite of post-Late Cretaceous rocks. The age span of the older suite varies considerably from assemblage to assemblage, and the point in time that separates the two suites varies slightly. In the Peninsular Ranges, the older rocks were formed from the Paleozoic to the end of Late Cretaceous plutonism, and in the Transverse Ranges over a longer period of time extending from the Proterozoic to metamorphism at the end of the Cretaceous. Within the Peninsular Ranges a profound diachronous unconformity marks the pre-Late Cretaceous-post-Late Cretaceous subdivision, but within the Transverse Ranges the division appears to be slightly younger, perhaps coinciding with the end of the Cretaceous or extending into the early Cenozoic. Initial docking of Peninsular Ranges rocks with Transverse Ranges rocks appears to have occurred at the terminus of plutonism within the Peninsular Ranges. During the Paleogene there was apparently discontinuous but widespread deposition on the basement rocks and little tectonic disruption of the amalgamated older rocks. Dismemberment of these Paleogene and older rocks by strike-slip, thrust, and reverse faulting began in the Neogene and is ongoing. The Peninsular Ranges basement rock assemblage is made up of the Peninsular Ranges batholith and a variety of metasedimentary rocks. Most of the plutonic rocks of the batholith are granodiorite and tonalite in composition; primary foliation is common, mainly in the eastern part. Tertiary sedimentary rocks of the Los Angeles Basin crop out in the Puente and San Jose Hills along with the spatially associated Glendora Volcanics; both units span the boundary between the Peninsular Ranges and San Gabriel Mountains basement rock assemblages.
The San Gabriel Mountains basement rock assemblage includes two discrete areas, the high standing San Gabriel Mountains and the relatively low San Bernardino basin east of the San Jacinto Fault. The basement rock assemblage is characterized by a unique suite of rocks that include anorthosite, Proterozoic and Paleozoic gneiss and schist, the Triassic Mount Lowe intrusive suite, extensive deformed and undeformed Cretaceous granitic rocks, the Pelona Schist, and Oligocene granitic rocks. Internal structure of the assemblage includes the Vincent Thrust Fault, at least two old, abandonded segments of the San Andreas Fault system, and extensive areas of well-developed to pervasively mylonitized rocks.
The main body of the San Gabriel Mountains is bounded on the north by the San Andreas Fault and on the south by the Sierra Madre-Cucamonga Fault Zone. East of the San Jacinto Fault, the San Bernardino basin is an asymmetric pull-apart basin bounded by the San Andreas Fault on the east, and underlain by many of the same rock units that characterize the San Gabriel Mountains. Cretaceous and older rocks of the San Gabriel Mountains basement rock assemblage are divided into two structurally and lithologically distinct groups by the Vincent Thrust Fault, a regional, low-angle thrust fault that predates intrusion of Oligocene granitic rocks. The Vincent Thrust separates the Mesozoic Pelona Schist in its lower plate from highly deformed gneiss, schist, and granitic rocks in the upper plate. The fault, along with its far-offset, dismembered analogs in the Orocopia and Chocolate Mountains east of the Salton Sea, may underlie much of southern California.
Crystalline rocks between the Mill Creek Fault and the main trace of the San Andreas Fault Zone range from highly deformed gneiss of unknown age to relatively undeformed Mesozoic biotite-hornblende diorite. They are overlain by Miocene sedimentary rocks and cut by the Wilson Creek Fault, that is considered to be an older segment of the San Andreas Fault system. Crystalline rocks of this basement assemblage are similar to rocks in the Little San Bernardino Mountains to the southeast, and appear to have been displaced about 50 km by the Wilson Creek and Mill Creek Faults.
About 80 to 85 percent of the San Bernardino Mountains bedrock assemblage in the quadrangle is Mesozoic granitic rocks, and the rest, highly metamorphosed and deformed Late Proterozoic and Paleozoic metasedimentary rocks. There is a pronounced gradient from east to west, and to a slightly lesser degree from south to north, in the magnitude of both deformation and metamorphism of the Late Proterozoic and Paleozoic metasedimentary rocks. In addition to the east to west gradient of increasing metamorphism and deformation, east of the quadrangle there appears to be a sharp break between highly deformed and relatively undeformed Late Proterozoic and Paleozoic rocks.
Late Proterozoic and Paleozoic units comprise a thick sequence of metasedimentary rocks generally consisting of a lower quartzitic sequence and an upper carbonate rock sequence. The entire lower quartzitic part is Late Proterozoic and Early Cambrian, and includes the Stirling Quartzite, Wood Canyon Formation and Zabriskie Quartzite; the upper carbonate rock sequence includes the Cambrian Carrara and Bonanza King Formations, the Devonian Sultan Limestone, the Mississippian Monte Cristo Limestone, and the Pennsylvanian Bird Spring Formation.
Mesozoic intrusive rocks in the San Bernardino Mountains and southern Mojave Desert include numerous Triassic and Jurassic plutons. The Triassic rocks are relatively alkalic and quartz deficient, and contrast with the voluminous, quartz-rich, calc-alkalic Cretaceous granitic rocks, which make up the largest part of the San Bernardino Mountains assemblage. The voluminous tonalitic rocks in the San Gabriel Mountains and Peninsular Ranges assemblages are essentially absent in the western San Bernardino Mountains. Many areas of dominantly Cretaceous granitic rocks are mapped as Mesozoic mixed-rock units, because they are extremely heterogeneous, and include large components of older rocks.
The relatively young, active San Andreas Fault system is by far the dominant structure in the San Bernardino quadrangle. Based on offsets of many of the rock units found in the San Bernardino quadrangle, different amounts of lateral displacement have been proposed for the San Andreas Fault system within and south of the Transverse Ranges. The Neogene evolution of the Transverse Ranges Province, and its relationship to the San Andreas Fault system in particular, are complicated by several abandonded segments and the shifting locus of the fault during the late Cenozoic. Most recent structural interpretations require relatively large rotations within the Transverse Ranges Province.
Other active faults in the quadrangle include the San Jacinto Fault and the reverse faults bounding and within the Transverse Ranges. Older faults considered to be abandoned segments of the San Andreas Fault system include the San Gabriel Fault, Punchbowl Fault, Mission Creek Fault, and Wilson Creek Fault. The Vincent Thrust and Squaw Peak Fault are both older faults, the Vincent probably of late Mesozoic to early Tertiary age.
Map nomenclature: 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.
Map plot: Some contacts are very poorly located or are gradational over a very wide interval. Many of these contacts would normally be shown as scratch contacts, but at 1:100,000 scale lead to unclear map relationships. For the purposes of clarity, these scratch contacts are drawn on the map plot with a short dashed line. Dune crests within units Qoed3 and Qyed1 are mapped and recorded in the database, but are omitted from the geologic map plot file, because they obscure unit contacts. Dikes making up unit Kg are mapped and recorded in the database, but are omitted from the geologic map plot file because they are too concentrated and plot as a mass of indistinguishable lines. Intra-unit grain-size boundaries within generic Quaternary units are recorded in the database, but are in most cases poorly defined and poorly located, because the contacts are anastamosing and gradational. They also are omitted from the geologic map plot file.
Use of this digital geologic-map database should not violate the spatial resolution of the data. Although the digital form of the data removes the constraint imposed by the scale of a paper map, the detail and accuracy inherent in map scale are also present in the digital data. Use of this digital geologic map should not violate the spatial resolution of the data. The San Bernardino 30' x 60' database was compiled from many sources including: (1) 1:62,500 reconnaisance mapping, (2) mapping from 1:24,000 USGS Open-File releases, (3) unpublished 1:24,000 mapping (4) Quaternary mapping from interpretation of 1:24,000 aerial photography, and (5) detailed 1:9,600 and 1:12,000 mapping from California Geological Survey Open-File releases. See Sheet 5, figure 3 for detailed sources of mapping. Any enlargement beyond the spatial resolution of the original geologic source data violates the spatial resolution of the data. Similarly, the digital topographic base data are derived from the U.S. Geological Survey, 1:100,000-scale San Bernardino 30' x 60' Digital Line Graphs (DLGs); any enlargement beyond this scale may be misleading. Where this database is used in combination with other data of higher resolution, the resolution of the combined output will be limited by the lower resolution data. No part of the database is intended to serve for site-specific studies.
Examination of a plot of the geologic map (Sheet 1) indicates detail in some areas that is far to fine to show well at 1:100,000 scale. This detail is purposely maintained to draw attention to areas where detailed information, compiled from large-scale maps is available. This detail may be viewed by on-screen examination of the digital map coverage or by plotting selected areas at larger scales. However, any enlargement beyond the spatial resolution of the original geologic source data violates the spatial resolution of the data.
Geologic mapping and digital preparation of this report were sponsored jointly by (1) the National Cooperative Geologic Mapping Program of the U.S. Geological Survey, and (2) the Southern California Areal Mapping Project (SCAMP).
Nation-wide geologic-map accuracy standards have not been developed and adopted by the U.S. Geological Survey and other earth-science entities. Until such standards are adopted, the SCAMP project has developed internal map-accuracy standards for 1:100,000-scale geologic maps produced by the project.
Geologic lines and points on 1:100,000 scale geologic maps are judged to meet SCAMP's internal map-accuracy standards if they are located to within +/-50 meters, relative to topographic or cultural features on the base map. On any derivative geologic-map plot, line data for faults that are judged to meet the SCAMP internal map-accuracy standard are denoted by solid lines; line data that may not meet the SCAMP internal map-accuracy standard are denoted by dashed or dotted lines. All non-fault contacts are represented by solid lines, and represent the same accuracy standards as their fault counterparts. The few non-fault dashed lines on the map represent very poorly located or highly gradational contacts, and are not as accurately located as their fault conterparts. There is no cartographic device for conveying the map-accuracy for geologic-point data (eg. symbols representing bedding, foliation, lineations, etc.).
The areal extent of the map is represented digitally by an appropriately projected (UTM 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.
In the course of the compilation, due to the varied detail of data sources, some units from these sources were combined to form composite units, and in some cases unit names were changed to conform to the most current usage or more recent geologic mapping. These changes and combining of units are noted and discussed in the Description of Map Units.
Geographic Information System (GIS) ArcInfo software developed by Environmental Systems Research Institute, Inc., (ESRI) v.8.1 on a SunOS, 5.8, sun4du UNIX system were used to process the work.
Ontario Morton, D.M. and Matti, J.C., Mapping and aerial photograph interpretation done 1990-1999. U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Guasti Morton, D.M. and Matti, J.C., Mapping and aerial photography interpretation done 1990-1999. U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Fontana Morton, D.M., Mapping and aerial photograph interpretation done 1990-1999. U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
San Bernardino South Morton, D.M. and Matti, J.C., Mapping and aerial photograph interpretation done 1990-1999. U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Redlands Matti, J.C. and Morton, D.M., Mapping done 1978-1998. U.S. Geological Survey, scale, 1:24,000 (paper)
Yucaipa Matti, J.C. and Morton, D.M., Mapping done 1978-1998. U.S. Geological Survey, scale, 1:24,000 (paper)
Azusa Morton, D.M., U.S. Geological Survey, mapping done 1990-1997, scale, 1: 24,000 (paper); Nourse, J.A., California State Polytechnic University, Pomona, mapping done 1997-2001, scale, 1:24,000 (base stable)
Glendora Morton, D.M., U.S. Geological Survey, mapping done 1990-1997, scale, 1: 24,000 (paper); Nourse, J.A., California State Polytechnic University, Pomona, mapping done 1997-2001, scale, 1:24,000 (base stable)
Glendora Bezore, S.P., California Geological Survey, mapping done 1997-1999, scale, 1:24,000. Compiled area also includes published mapping by Shelton, J.S. 1955 (paper)
Mount Baldy Morton, D.M., U.S. Geological Survey, mapping done 1988-1999, scale, 1: 24,000 (paper); Nourse, J.A., California State Polytechnic University, Pomona, mapping done 1997-2001, scale, 1:24,000 (base stable); Ehlig, P.L., mapping done 1955-1985, scale, 1:24,000 (paper)
Mount Baldy Morton, D.M., Matti, J.C., U.S. Geological Survey, mapping done 1988-1999, scale, 1:24,000 (paper)
San Bernardino North Matti, J.C., Quaternary mapping done 2000. U.S. Geological Survey, scale, 1: 24,000. (not included in published map) (paper, aerial photography, and base stable)
Harrison Mtn Miller, F.K., Morton, D.M., and Matti, J.C., Mapping done 1988-1999, 2000-2001. U.S. Geological Survey, scale, 1:24,000 (paper and base stable)
Keller Peak Miller, F.K., Morton, D.M., and Matti, J.C., Mapping done 1988-1999, 2000-2001. U.S. Geological Survey, scale, 1:24,000 (paper and base stable)
Crystal Lake Ehlig, P.L., mapping done 1955-1985, California State University, Los Angeles, scale 1:24,000 (paper); Nourse, J.A., mapping done 1996-2001, California State Polytechnic University, Pomona, scale, 1:24,000 (base stable); Morton, D.M., U.S. Geological Survey, mapping done 1990-1997, scale, 1:24,000 (paper)
Mount San Antonio Ehlig, P.L., mapping done 1955-1985, California State University, Los Angeles, scale 1:24,000 (paper); Nourse, J.A., mapping done 1996-2001, California State Polytechnic University, Pomona, scale, 1:24,000 (base stable); Morton, D.M., U.S. Geological Survey, mapping done 1990-1997, scale, 1:24,000 (paper)
Mount San Antonio Morton, D.M., U.S. Geological Survey, mapping done 1980-1990, scale, 1:24,000 (paper)
Cajon Morton, D.M., U.S. Geological Survey, mapping done 1980- 1999, scale, 1:24,000 (paper)
Silverwood Lake Miller, F.K. and Morton, D.M., mapping done 1996-2001, U.S. Geological Survey, scale, 1:24,000 (paper)
Lake Arrowhead Miller, F.K., reconnaissance mapping done 2000-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Juniper Hills Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Valyermo Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Mescal Creek Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Phelan Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Baldy Mesa Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Hesperia Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
Apple Valley South Morton, D.M. and Miller, F.K., reconnaissance mapping and aerial photography interpretation done 1999-2001, U.S. Geological Survey, scale, 1:24,000 (aerial photography and paper)
In addition to the customary software-defined attributes in each feature attribute table, user-defined attributes are included that allow the user access to more detailed geologic information including unit name, grain size where applicable, and rock assemblage. Two lookup tables are included: rockunit_color.lut (rockunit color assignment) and rockunit_pattern.lut (rockunit pattern assignment).
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 the delivery, installation, operation, or support by USGS.
This digital, geologic map database of the San Bernardino 30' x 60' quadrangle, 1:100,000 map-scale, and any derivative maps thereof, is not meant to be used or displayed at any scale larger than 1:100,000 (e.g., 1:24,000).