historical geology field assignment

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.


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


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


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


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


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.


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


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).


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.


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

historical geology field assignment

Education

soda lake figure

barn owls

temblor range figure

barn owl feeds

barn owl populations

formation of soda lake

shores of soda lake

owl species