historical geology field assignment
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1Running head: HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
Historical Geology Field Assignment: Carrizo Plain
Elouise M. Hurst
West Hills Community College
2HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
Abstract
For the Historical Geology Field Assignement, I visited the Carrizo Plain National Monument in
San Luis Obispo County, California. The five subjects I picked were the overall history of the
Carrizo Plain, Soda Lake, saltbush plants, barn owls and the San Andreas Fault.
3HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
Historical Geology Field Assignment: Carrizo Plain
The Carrizo Plain National Monument, located approximately 100 miles north of Los
Angeles, encompasses 250,000 acres of grassland valley. On its eastern side it is bordered by the
Temblor Range and by the Caliente Range on its western side. The San Andreas Fault runs the
length of the eastern margin; along the western edge of the Temblor Range (Figure 1). Soda
Lake, a 3,000 acre seasonal alkali lake, lies in the northern portion of the plain.
This area was originally a shallow to intermediate depth marine basin which was uplifted
during the Pleistocene. Marine sedimentary rock, both non-organic and organic, is the
predominate rock of both the Temblor and Caliente Ranges (Geology, 1999).
Figure 1: Soda Lake with Temblor Range
4HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
The entire Carrizo Plain area drains internally (Hildinger, 1995). The water from the
western slopes of the Temblor Range and the eastern slopes of the Caliente Range all drain into
the Carrizo Plain. This water collects on the valley floor and creates Soda Lake and many other
small pools and ponds. Soda Lake (Figure 2) is not the remnant of a large ice age lake but was
formed due to uplift associated with the San Andreas Fault. Between 3-1 million years ago the
river formed from the runoff flowed southward out of the valley. Uplift to the south caused the
river to change direction and flow northward. Uplift to the north then blocked the river and led to
the formation of Soda Lake.
Figure 2: Soda Lake
5HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
During the late summer months or earlier in years of low precipitation, Soda Lake dries
up. The crust (Figure 3) left behind is a mixture of salts; 82% sodium sulfate, 9% sodium
chloride and 9% miscellaneous salts (Hildinger, 1995). The salts have accumulated from erosion
of the surrounding mountains that were transported by runoff and evaporated on the valley floor.
Figure 2: Salt Crust
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Figure 4: Saltbush
Saltbush (Figure 4) is a native plant of California and is found only from San Luis Obispo
to Fresno, CA (Wilson, 2011). It is found lining the shores of Soda Lake and other low-lying
areas on the Carrizo Plain where water collects in the spring.
This species, Atriplex spinifera, has evolved to thrive under harsh conditions. It does best
under water-stress conditions such as drought and salt. Under extreme drought conditions it will
shed its leaves. Saltbush removes the salt from the water and stores it in bladders located in its
7HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
leaves (Wilson, 2011). When the leaves are shed or are eaten by animals, the salt is then removed
from the plant.
Figure 5: Barn Owl
Figures 5 and 6 are photographs of Barn Owls. The Barn Owl (Tyto alba) is found on
every continent except Antarctica. It is the most wide spread of all owl species and very adaptive
to many environments. They prefer primarily open lowlands with some trees like farmland and
semi-arid shrub lands but are also found in various forest types and urban areas (Behrman,
2011).
The fossil record of the barn-owl goes back to the Eocene and then showing a decline in
the Neogene. The first time the barn owl was official described was in 1769 by Giovanni
Scopoli, an Italian naturalist. There are currently 16 known species of barn owl in the world.
8HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
The Barn Owl has adapted to feed on a wide variety of food sources. While the Barn Owl
feeds mostly on small mammals such as mice, voles, squirrels and skunks, they have also been
documented to feed on lizards, fish, birds and insects.
Certain areas such as Connecticut have seen a decline in Barn Owl populations. This is
due to loss of foraging and nesting habitat and the increased use of rodent poison which has
reduced the owls’ food base. Currently the Barn Owl is listed as an endangered species in the
state of Connecticut (Connecticut, 2011).
Figure 6: Barn Owl
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Figure 7: Wallace Creek Offset
The San Andreas Fault is the longest fault in California; measuring nearly 800 miles. The
fault runs along the western edge of the Carrizo Plain along the lower portion of the Temblor
Range. The San Andreas Fault was formed during the Cenozoic Era by the collision of the
Pacific plate with the North American plate (Levin, 2010). Instead of the Pacific plate being sub
ducted under the North American plate, it started a lateral or strike-slip motion. The land mass
west of the fault is moving in a generally northward direction at about 2 inches per year (Schulz,
1997). This rate is not fixed along the entire length of the fault as some sections slowly creep
each year while others lay dormant for long periods of time and move with earthquakes.
Geologists believe that since the formation of the San Andreas Fault 15-20 million years ago, the
total movement of the fault is 350 miles (Schulz, 1997).
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Figure 7 shows the offset caused by the San Andreas Fault. Wallace Creek flows across
the fault and its path has been altered by the plate movement. During runoff, the water flows
from right to left in the picture. In the last 3,800 years, Wallace Creek has been offset
approximately 420 feet by the San Andreas Fault.
11HISTORICAL GEOLOGY FIELD ASSIGNMENT: CARRIZO PLAIN
References
Behrman, L. (2011). Barn Owl. Retrieved from
http://www.peregrinefund.org/explore_raptors/owls/barnowl.html
Carrizo Plain National Monument. (2011, April 25). Retrieved from
http://www.blm.gov/ca/st/en/fo/bakersfield/Programs/carrizo.html
Connecticut Department of Environmental Protection. (2011). Barn Owl. Retrieved from
http://www.ct.gov/dep/cwp/view.asp?q=325962
Geology and Paleontology. (1999). Retrieved from
http://www.blm.gov/pgdata/etc/medialib//blm/ca/pdf/pdfs/bakersfield_pdfs/
bake_cpnaplan.Par.4e448b5d.File.pdf/GeologyPaleontology.pdf
Hildinger, J. (1995). Carrizo Plain Natural Area. Retrieved from
http://www.scec.org/wallacecreek/guides/blm-cpna.pdf
Levin, H. (2010). The Earth Through Time. Hoboken, NJ: John Wiley & Sons, Inc.
Schulz, S. (1997, June 24). The San Andreas Fault. Retrieved from
http://pubs.usgs.gov/gip/earthq3/safaultgip.html
Wilson, B. (2011). Atriplex spinifera. Retrieved from http://www.laspilitas.com/nature-of-
california/plants/atriplex-spinifera
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