Preliminary geologic map of the San Bernardino 30' x 60' quadrangle, California (includes preliminary GIS database)

The San Bernardino 30'x60' quadrangle, southern California, is diagonally
bisected by the San Andreas Fault Zone, separating the San Gabriel and San
Bernardino Mountains, major elements of California's east-oriented Transverse
Ranges Province. Included in the southern part of the quadrangle is the northern
part of the Peninsular Ranges Province and the northeastern part of the
oil-producing Los Angeles basin. The northern part of the quadrangle includes
the southern part of the Mojave Desert Province. Pre-Quaternary rocks within the
San Bernardino quadrangle consist of three extensive, well-defined basement rock
assemblages, the San Gabriel Mountains, San Bernardino Mountains, and the
Peninsular Ranges assemblages, and a fourth assemblage restricted to a narrow
block bounded by the active San Andreas Fault and the Mill Creek Fault. Each of
these basement rock assemblages is characterized by a relatively unique suite of
rocks that was amalgamated by the end of the Cretaceous and (or) early Cenozoic.
Some Tertiary sedimentary and volcanic rocks are unique to specific assemblages,
and some overlap adjacent assemblages. A few Miocene and Pliocene units cross
the boundaries of adjacent assemblages, but are dominant in only one. Tectonic
events directly and indirectly related to the San Andreas Fault system have
partly dismembered the basement rocks during the Neogene, forming the modern-day
physiographic provinces.

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