Geologic map and digital database of the Redlands 7.5' quadrangle, San Bernardino and Riverside Counties, California

The Redlands 7.5' quadrangle is located in the southeastern margin of the San Bernardino
Basin, an extensional region situated in a right-step-over zone within the San Andreas
Fault system. The quadrangle is traversed by several important fault zones, including:
(1) northwest-trending right-lateral strike-slip faults of the San Andreas system
(Banning Fault, the Mission Creek and San Bernardino Strands of the San Andreas Fault,
the San Jacinto Fault); (2) northeast-trending normal dip-slip faults that have
downdropped the San Bernardino Basin; (3) east-trending contractional faults of the San
Timoteo Canyon Fault zone. Some of these faults bound distinctive packages of
crystalline basement rock.
Northwest of the Mission Creek Strand of the San Andreas Fault lies an igneous and
metamorphic complex characterized by textural and compositional heterogeneity. This
terrane, the Wilson Creek block, is strongly gneissose but includes foliated to massive
granitoid rocks intimately intermingled with the gneisses. Thin slices of the gneissose
complex have been displaced a few kilometers by the San Bernardino Strand of the San
Andreas, the modern trace of the San Andreas Fault in the Redlands quadrangle and
elsewhere along the southwest margin of the San Bernardino Mountains.
The Mission Creek strand is inferred to lie beneath Quaternary surficial deposits along
the southwestern base of the San Bernardino Mountains. This fault is the major strand
of the San Andreas Fault zone, has about 100 km of right-slip, and has juxtaposed
distinctive crystalline rocks of San Gabriel Mountains-type against the Wilson Creek
block and the San Bernardino Mountains.
The Banning Fault probably demarcates an important boundary between rocks of San Gabriel
Mountains-type to the north and rocks of Peninsular Ranges-type to the south. This
hypothesis is difficult to test because outcrops of the two terranes are several miles
apart and between them the trace of the Banning Fault must be inferred beneath surficial
deposits and beneath the San Timoteo beds of Frick (1921). The rocks of Peninsular
Range-type are very different from those of San Gabriel Mountains-type, and consist of
massive to foliated granitoids of monzogranitic, granodioritic, and tonalitic
composition.
Much of the Redlands quadrangle is covered with unconsolidated Quaternary surficial
deposits of sand and gravel that have accumulated over the last 600,000 years or so.
These are thickest on the modern and ancestral flood plains of the Santa Ana River. In
the south part of the quadrangle within the San Timoteo and Reche Canyon drainage
systems, Quaternary surficial deposits are less extensive and have distribution patterns
determined by displacements on the San Timoteo Canyon Fault zone (reverse faulting) and
the San Jacinto Fault (strike-slip faulting). In this region, folded and faulted
deposits of the San Timoteo beds of Frick, (1921) formed upwarps and downwarps that
influenced the evolution of the landscape and its sedimentary deposits.
Digital Data:
This geologic database of the Redlands 1:24,000-scale 7.5' quadrangle, San Bernardino
and Riverside Counties, California, was prepared by the Southern California Areal
Mapping Project (SCAMP), a geoscience project sponsored jointly by the U.S. Geological
Survey (USGS) and the California Geological Survey. The database was created in
ARC/INFO (Environmental Systems Research Institute), and includes the following files:
(1) a readme file, (2) this metadata file, (3) coverages containing geologic-map data
and station-location data, (4) associated data tables, (5) a browse graphic of the
geologic-map plot and map-marginal explanatory information (.pdf file), (6) a PostScript
graphics file of the geologic-map plot with map-marginal explanatory information, and
(7) .pdf files describing map units of the Redlands quadrangle (Description of Map
Units) and their geologic age and correlation (Correlation of Map Units).