Re: [DL] California's geography and climate... [Long]

[Soothsprayer <hercubadger@yahoo.com>]

Funnily enough, I was working on this today for a
report. It's long, geo-intensive and generally dull so
grab a coffee before attempting to read. It all
relates to California now, not the Deadlands revision.

Cheers,
Mr. B



[Regional Topography/Drainage]
The subject site lies within the Central or Great
Valley of California.   The Great Valley is an
elongate lowland located between the Sierra Nevada on
the east and the Coast Ranges on the west.  The
southern portion of the Great Valley drained by the
San Joaquin River is referred to as the San Joaquin
Valley and the northern portion drained by the
Sacramento River is referred to as the Sacramento
Valley.  The Great Valley is approximately 400 miles
long and approximately 50 miles wide and occupies the
central portion of the State of California.  It
extends from just north of Redding down to
approximately 20 miles south of Bakersfield.  Only two
major topographic breaks occur in the otherwise
relatively monotonous valley floor: the Kettleman
Hills in the San Joaquin Valley and the Sutter Buttes
in the Sacramento Valley.  Aside from these two
features, the entire valley lies between sea level and
500 feet in elevation.  The sole external drainage
from the valley is located southwest of Sacramento,
via the Sacramento River, through the Carquinez Strait
to San Francisco Bay.

[Regional Geology]
Rocks of the Great Valley consist of sedimentary
deposits ranging in age from late Mesozoic through
Holocene (Recent). The geology of the Great Valley is
relatively well understood due to the extensive
geophysical data that has been gathered during several
decades of oil and gas exploration and the high number
of oil and gas wells.  Prolific oil and gas production
has been established throughout the valley and dates
from the mid-1800’s.

The Great Valley is an asymmetrical synclinal trough
with its axis offset to the west.  The valley may be
divided into two roughly parallel belts.  The eastern
belt consists of undeformed alluvial fan and lake
deposits thinning to the west from the Sierra Nevada
front.  The western belt consist of deformed Mesozoic
and Cenozoic rocks dipping east into the valley from
the Coast Ranges.  Two major cross-cutting structural
features are the Stockton arch and the White Wolf
fault in and south of the Bakersfield arch.  Numerous
other lesser faults are known in the valley and
several are known to be currently active.

The geologic history of the Great Valley began with
Jurassic sedimentation towards the west from the
rising Sierra Nevada mountains.  Deposits include
shallow marine sands and shales in the east and deeper
marine clastics, volcaniclastics, and intrusives in
the west. The latter are represented by the Franciscan
Formation in outcrops in the Coast Ranges west of the
valley.  Marine deposition continued throughout the
Mesozoic.  Cenozoic deposition was accompanied by
regional deformation in the north and localized
intense deformation in the south.

By the Pliocene, most of the marine waters had
retreated from the valley and the valley was occupied
by numerous brackish and fresh water lakes.  This
pattern persisted until the present, when the climate
became much more arid and the lake beds dried up.  As
a result, numerous playa lakes (dry lake beds) are
scattered among fluvial, alluvial fan, and dune sand
deposits of Quaternary age.

[Regional Hydrogeology]
Unconsolidated continental deposits constitute the
primary source of groundwater in the Great Valley.  
The continental deposits consist primarily of
alluvium, however, some areas consist of permeable
lake bed sediments.

Within the central, western, and southeastern portions
of the San Joaquin Valley, the groundwater may be
subdivided into three informal units.  In downward
succession these are (1) unconfined and semi-confined
alluvial units of Holocene, Pleistocene, and possibly
late Pliocene age; (2) a widespread diatomaceous clay
bed of Pleistocene age that acts as a confining layer
to alluvial and lacustrine beds of Pleistocene and
late Pliocene age; and (3) saline connate water in
marine sediments of middle Pliocene age and older
units.  In the eastern part of the valley, the
diatomaceous clay layer is not present and units (1)
and (2) are both generally unconfined to
semi-confined.  Those areas lacking the diatomaceous
clay layer include the porous alluvial fans of the
major streams that drain westward from the Sierras,
such as the Stanislaus, Tuolumne, Merced, King,
Kaweah, and Kern rivers. South and east of the Kern
River, the deeper Pleistocene and Pliocene age
aquifers are confined beneath lacustrine clay layers
and finer-grained alluvial deposits.

In summary, coarse-grained well-sorted alluvial units
predominate near the canyon mouths of the streams
draining west from the Sierras into the valley.  Areas
progressively removed from the canyon mouths exhibit
finer-grained and more poorly sorted aquifers with
lower groundwater yields.  The stream channels act as
areas of recharge, as do irrigation canals and heavily
irrigated agricultural land in the valley.

Groundwater flow direction is generally towards the
west, to the lower part of the valley, then towards
the north; mimicking surface drainage.  Near major
rivers, groundwater flow is generally towards the
river.  Locally, flow direction may be influenced by
the presence of irrigation canals, streams, irrigated
land, and areas of extensive pumping.  

Depth to groundwater varies due to the same factors
cited above.  Groundwater mapping performed in 1952
showed groundwater depths to be a few tens of feet
below the ground surface in the Buena Vista Lake bed
area in the southwestern portion of the valley. In
contrast, depth to groundwater exceeded 350 feet along
the Sierra Nevada and Coast Range mountain fronts. 
Several local depressions of the groundwater table
exceeding 200 feet were also noted near major towns
such as Bakersfield and Fresno


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