Cholame Segment of the San Andreas Fault ZoneThe Cholame segment of the San Andreas Fault system is a 56km

stretch bounded to the northwest by the Parkfield segment and to the southeast by the Carizzo segment. This area is important as it is the tran-

sitional zone between the partially creeping Parkfield segment and the locked Carrizo segment. Parkfield and Carrizo exhibit significant rupture behavior differences. Until fairly recently there had been little paleoseis-

mic data here for several reason, including inaccessibility, poor conditions for historical seismic recording and detrimental human activity altering what little evidence that did exist. Within the last decade however, dis-

covery of paleoseismic evidence through trench logging, as well as analy-sis of historical cadastral surveying has provided new information that tends to refute prior estimations of slip rate and event magnitudes that

had been heretofore based solely on geomorphic evaluation techniques. This new evidence suggest slip offsets from the 1857 M8 Fort Tejon

quake in the Cholame segment to be significantly larger than the offset amount suggest by Sieh, 1978 of ~3-4 m. This has significant ramifica-

tions for estimating recurrence intervals.

Abstract

The area of the San Andreas fault from San Juan Bautista to an area a few kilometers Northwest of Parkfield is an area of gradual creep. The plane along the fault moves but not through large seismic activity, just

continual slippage and microseismicity. The Parkfield zone to the southeast is an area considered to be partially creeping. Meaning

medium sized events occur on a regular basis around every 22 years. The Cholame segment is the bridge from this creeping/locked Parkfield zone to the locked Carrizzo section. In this case, locked means there

is no gradual regular movement or small size quakes, but rather a buildup of strain energy over hundreds of years and then the release of

that energy in a single large event. The Cholame segment has not been studied much until recently and may provide clues that help

dispel the thought of a single fault model for the San Andreas in this area.

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In this Dibblee map, which is centered around the town of Cholame and Highway 46 you can see a striking example of en-echelon fissuring up to 7 feet long and 9

inches wide. These cracks appeared some days (or minutes, unclear as to

which) prior to the June-July 1966 M5.6 quake.

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Cholame Creek

Park�eld

Hwy 46 Cholame

Hwy 58

Wallace Creek

Van Matre

Ranch

Hwy 166

Santiago Canyon

Mil Potre

ro

Cuddy Valley

Frazier Park

Tejon Pass

Lake Hughes

Lake Elizabeth

Leona Valley

Lake Palmdale

Littlerock Creek

Pallett C

reek

Valyermo - B

ig Rock

Wrightw

wood

Cajon Creek

Cable Canyon

Devil Canyon

Waterman Canyon

City Creek Highland

1857 Fault O�sets along San Andreas Faultadapted from Sieh, K. 1978

Carrizo PlainCholame Valley

Cholame Segment

Bitter- water Valley LY4 Site

Cadastral Survey Site

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50 100 150 200 250 300 350 0 km

This classic work by Kerry Sieh from 1978 has been the gold standard of offset values attributable to the great 1857 quake. It was derived entirely by geomorphic landform ob-servation with the exception of a couple of pieces of dendrochronologic evidence. As

you can see there is a void or leap of faith from the observable 3 meter offset in the Bit-terwater Valley (part of the Cholame segment) to the 8-9 meter offset in the Carrizo

plain segment. What happened?? No surface observable evidence between these two segments? Recent paleoseismic studies hope to fill in some of these blank areas. The area around Las Yeguas Canyon (LY4) has been the subject of recent trenching activity. Just to the northwest of LY4 a comparison of pre and post 1857 event surveys indicate

1857 offset to be 16.2 +- 6.0m. This is a huge variation from Sieh 3-4 meter range. This cadastral survey study is a broad aperture view, 2km whereas the geomorphic ob-servations of Sieh are narrow aperture of 20m. Lienkaemper (2001) believes the 3-4 meter value is too low and should be around 5-7m. He bases this on more detailed

study of the geomorphic features in the Cholame segment. This has huge ramifications regarding recurrence intervals and predictions

In a bigger picture view, the Pacific plate is moving northwest in relation to the North American plate at a rate of 46 mm/yr. In the area of the northwest end of

the 1857 rupture, the San Andreas fault zone ac-counts for about 70% of this slippage; this results in about 33 mm/yr of slip in this zone. The subparallel Rinaconda Fault Zone may accommodate some of

the remaining 13mm/yr of slip.

Lienkaemper, J.J., and T.A. Sturm, Reconstruction of a chan-nel o�set in 1857(?) by the San Andreas Fault near Cholame, California, Bulletin of the Seismological Society of America, 79 (3), 901-909, 1989.

Lienkaemper, J.J., 1857 Slip on the San Andreas Fault South-east of Cholame, California, Bulletin of the Seismological So-ciety of America, 91 (6), 1659-1672, 2001.

Runnerstrom, E. E., Grant, L. B., Arrowsmith, J R., Rhodes, D. D., and Stone, E. M., Displacement across the Cholame seg-ment of the San Andreas Fault between 1855 and 1896 from cadastral surveys, Bulletin of the Seismological Society of America: Special Issue on Paleoseismology of the San An-dreas fault, 92, 2,659-2,669, 2002.

Sieh, K.E., Slip along the San Andreas fault associated with the great 1957 earthquake, Bulletin of the Seismological So-ciety of America, 68, 1421-1448, 1978b.

Stone, E.M., Grant, L., and Arrowsmith, J R., Recent rupture history of the San Andreas Fault southeast of Cholame in the northern Carrizo Plain, California, Bulletin of the Seismologi-cal Society of America, 92, 983-997, 2002.

Young, J. J., Arrowsmith, J R., Colini, L., Grant, L. B., and Gootee, B., 3-D excavation and measurement of recent rup-ture history along the Cholame segment of the San Andreas Fault, Bulletin of the Seismological Society of America: Spe-cial Issue on Paleoseismology of the San Andreas fault, 92, 2,670-2,688, 2002.

Why the data void?

Predicitions?

Homage to James Dean

Dibblee Map around Cholame

ReferencesRelationship to Major Features

Creep to Locked Bridge Overview

Event Ages

There are four important considerations for choosing paleoseismic (trenching) sites:1. Frequent deposition of bedded sedi-ments2. Production and preservation of datable material (charcoal, peat, pollen)3. A well defined fault trace4. A well located fault traceIn the Cholame segment it has been diffi-cult to finds sites that that have the fea-tures listed above. There are no good peat forming locations and patterns of deposi-tion do not lend themselves to preserving charcoal.Cattle ranching and climate change have modified the erosion and deposition pat-terns in the area. There are few incised drainages that cross the fault that are younger than the 1857 event and hence are not offset.A predominant portion of this segment , es-pecially in the southern end has geomor-phic characteristics of a rift valley and the stream channels run parallel to the fault.Finally, most of the land in this segment is owned by cattle ranchers who are not re-searcher friendly, so access is difficult. One exception is Darrel Twisselman who has allowed access to the LY4 site.

Actor/Icon James Dean was killed in a traffic accident on September 30, 1955 in Cholame, Ca. on the

present day Highway 46. His Porsche 550 Spyder was hit head on by a car driven by Donald Tur-nupseed, a student from Cal Poly

San Luis Obispo. James Dean had only 3 major movies but all are clas-sics, Rebel Without a Cause, East of Eden and Giant. He received Academy Award nominations for best actor in two of them. If you like There Will be Blood, then you

must see Giant, a story about an oil discovery in Texas.

A table from our textbook showing the extent of missing data and unac-counted for events, not only in the Cholame segment but along much of

the fault.

If using 3-4m of offset of Sieh then the recurrence interval is 103 years == 3.5m/3.4cm/yr.

1857 + 103 = 1960 hmmm.. come and gone Using Linkaemper’s 5-7m offset then the recurrence interval

is 170 years == 5.8m/3.4cm/yr.1857 + 170 = 2027 Yikes!!

Mike Tacsik Geol 533November 4, 2010

Cholame

Cholame - sha-lambA Salinan Indian

word meaning “The Pretty One”.