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GEOLOGY IN OUR BACKYARD - THE KERN
RIVER VALLEY and
SOUTHERN SIERRA NEVADA
Dr. Jason and Ms. Zorka Saleeby
Division of Geological and Planetary Sciences
and the Caltech Tectonics Observatory, California Institute of
Technology, Pasadena CA 91125
The geology that one can observe in the Kern Valley-South Fork Valley
area may be thought of as developing in three major phases. The latest
phase occurred over the past approximately 20 million years (m.y.) with
much action in the past 2 m.y. This phase of geologic history has
rendered the landscape that we now observe with the relatively narrow
north-south trending Kern Valley, and the broader east-west trending
South Fork Valley. Both Valleys are controlled by groups of faults. The
South Fork Valley faults were active mainly between 20 and 15 m.y., with
a dominant set trending northwest-southeast, and a subordinate set
trending northeast-southwest. Most of these faults have undergone
substantial erosional modification resulting in a relatively open
valley. Such faults are widely distributed across the southern Sierra
Nevada, south of the Kernville area, as well as within the southern San
Joaquin basin. They commonly terminate against the north-south trending
Kern Canyon fault (KCF), which assisted with their 20-15 m.y. movement
patterns by making small adjustments in response to their differential
motions. Some time after 3.5 m.y. ago the KCF, including its
Breckenridge segment, began a major phase of west-side-up vertical
displacement that uplifted the Breckenridge Mountain and Greenhorn
Mountains region. The lower Kern River gorge began to incise its deep
channel as a response to this uplift, and the South Fork Valley was
partially filled with sediments due to natural damming along the KCF.
Additional north-south trending vertical motion faults formed parallel
to the KCF resulting in the Kern Valley. The youthfulness of these
faults give the Kern Valley its steep profile. The fault controlled Kern
Valley controlled the main course of the Kern River. Unlike most major
river canyons of the Sierra Nevada the main valleys of the Kern River
are strongly controlled by local faulting.
Stepping back in geologic time to the period of 100 to 85 m.y. we
venture into the phase of geologic history that produced most of the
hard crystalline rocks that the valleys of the Kern drainage were carved
into, and which form the greater Sierra Nevada. These rocks consist of
various granites that formed by the upward emplacement, coalescence and
solidification of hundreds of balloon and dike like magma bodies that
were generated about 50 miles deeper than their current resting site at
the Earth’s surface. The granitic magmas formed in response to the
underthrusting (subduction) of ancient Pacific ocean floor beneath the
western edge of North America, which delivered trapped ocean water and
sediments to depth under the future Sierra Nevada region. These wet
materials promoted melting at the base of the crust and the formation of
granitic magmas, which rose to within 10-20 miles of the Earth’s
surface, back then. The KCF originated at this time taking up horizontal
and vertical displacements in response to irregularities in the surface
morphology and the subduction trajectory of the Pacific ocean floor that
was underthrusting eastwards beneath the region. For example, in the
South Fork Valley area granites east of the KCF formed at roughly 15
miles deep, while those to the west at roughly 8 miles deep, even though
currently the west side of the KCF is moving up. The early KCF
profoundly influenced the manner in which the granites were denuded of
their overburden.
The earliest phase of geologic history that may be observed in the
region is recorded in metamorphic rocks that represent the environment
into which the granitic magmas rose. Some of these rocks are readily
observed at a distance for they make the impressive grey marble spires
and ridge line bands of the region. The starting materials for these
metamorphic rocks were laid down as sediments in shallow seas in two
main episodes spanning roughly 500-400 m.y. and 240-170 m.y. During the
early period of deposition sands derived from the ancient interior of
North America accumulated on a broad marine shelf. The resulting
sedimentary rocks were deformed and partly eroded between 300-250 m.y.,
and then re-submerged to be covered by the younger sedimentary sequence
that was compositionally more variable with sands, muds, silts, volcanic
ashes and limestones, the later of which were produced by corals, shell
fish and algae. The resulting composite sequence of sedimentary rocks
was highly deformed and metamorphosed into quartzite, schist and marble
when the granitic magmas rose into the area between 100 and 85 m.y. ago.
The igneous granites and their metamorphic host rocks underwent an early
phase of rapid denudation between 85 and 75 m.y. ago, and then very slow
erosion between 75 m.y. ago and the onset of the 20 m.y. and younger
faulting. This geologically young phase of faulting, along with stream
erosion of the Kern River drainage, has carved out the three dimensional
exposures that we have today through the igneous and metamorphic bedrock
of the region.
Dr. Jason and Ms. Zorka Saleeby have been examining
the terrains of the Southern Sierra and Southern San Joaquin
Valley for over 30 years. Dr. Saleeby is one of the experts in the basic geology video
series "Earth Revealed," where his down to earth (no pun
intended) teaching style allows for understanding of an
otherwise difficult topic.
Dr. Saleeby's research includes: Regional
field, petrologic and radiogenic isotopic and geochronologic
studies applied to the interactions of oceanic and continental
plates, tectonic and magmatic accretion of continental crust,
dynamics of continent edge batholithic belts and the
paleogeographic development of western North America;
petrogenesis and geodynamic setting of the upper mantle beneath
the Sierra Nevada region based on studies of Neogene volcanic
hosted xenoliths integrated with regional geophysical studies;
tectonic and petrogenetic development of the Greater Caucasus
Mountain Range, southern U.S.S.R. and its relations with the
paleogeographic evolution of the northern Tethys ocean basin;.
study of pre-industrial levels of Pb in human bone and tooth
remains from ancient ice burials as a base line for the study of
anthropogenic global Pb pollution.
Dr. Saleeby is a professor of Geology at
CalTech in Pasadena. He teaches introductory and advanced
geological field mapping, structural geology, physical geology,
Cordilleran regional geology and tectonics, global mountain
building and plate tectonics, application of petrogenetic and
geochemical studies to regional and global tectonics. He earned
his PhD in Geology from the University of California at Santa
Barbara. His dissertation was on "Structure, Petrology and
Geochronology of the King-Kaweah Mafic-Ultra mafic Belt,
Southwest Sierra Nevada Foothills, California."
Ms. Saleeby received an Engineer of
Geology Degree, Zagreb University, Croatia and an M.S. in
Geology at Indiana University.
She worked as a Senior Geologic Engineer with Shell Oil and Cal
Resources, Bakersfield (1990-1997), private consultant,
1997-1999, and is currently a Staff
Geologist, Caltech Tectonics Observatory.
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Birding the Kern River Valley & Southern Sierra Nevada
Bob Barnes
Kern River Valley Birding
Ridgecrest, CA
Bob Barnes has been birding through California for
the past 35 years. His expertise in Southern Sierra species distribution
and status is unparalleled. He has led over 200 local birding tours, and
spends countless hours independently birding the region. He authored the
section on Kern River Valley and Southern Sierra Nevada birding in "A
Birder's Guide to Southern California" by Brad Schram. Bob was integral in bringing the South Fork
Valley to the attention of Audubon and The Nature Conservancy resulting
in protection of this precious resource. He also worked on the Desert
Protection Act which added thousands of acres of protected wilderness to
Kern County's deserts and the southern Sierra Nevada.
He serves as the Field Trips Chair for
the
Spring Nature Festival. Since 2004, Bob has worked on
birding/wildlife tourism development project teams in Missouri,
northwestern and southern Nevada, and
Pennsylvania. He was the Meeting Chair for
the June 26-29, 2008 North American Butterfly Association (NABA)
Biennial Meeting which was held in the Kern River Valley; the first time
this national meeting was held in California. He also organizes
custom tours to Costa Rica and serves on the board of the
Kern River Valley Heritage Foundation.
Bob is an independent Biological Consultant and
serves as the Executive Director of the Arthur & Sidney R. Barnes
Foundation; which works to sustain the unique cultural and environmental
character of rural communities facing rapid development , especially
along California's Highway 178 Corridor from Death Valley National Park
through the Kern River Valley to Bakersfield. |
