Aerial Reconnaissance of Stream Terraces and Landslides

within Bitterwater Creek Watershed in Kern County, California

A Senior Project

presented to the Faculty of the Natural Resources Management and Environmental Sciences Department

California Polytechnic State University, San Luis Obispo

In Partial Fulfillment

of the Requirements for the Degree

Earth Science; Bachelor of Science

by

Zachary Smith

May, 2011

© 2011 Zachary Smith Introduction

The California Coast Ranges are relatively recent formations, possibly still being formed, and the understanding of their development is still incomplete. The process of hillslope formation requires uplift, through volcanism, folding, and/or faulting, and subsequent erosion. By looking at a hill's morphology it is possible to understand how it developed and what local forces were involved. For this report I have mapped landslides, fluvial surfaces, and stream terraces within the Bitterwater creek watershed which can later be dated and used to advance the understanding of hillslope development, local tectonism, and climate of California’s Coast Ranges.

Study Area

The area of interest for this study is the

Bitterwater creek watershed (fig. 1). The

Bitterwater creek watershed is located within

Kern County, California, as part of the southernmost extent of the Temblor Range.

The Temblor Range parallels the east side of the San Andreas Fault and is the easternmost set of the Coast Ranges. It is estimated that the whole of the coastal ranges began to form starting ~ .4 Ma due to compressional stress Figure 1. Location of Bitterwater Creek watershed normal to the SAF and resultant thickening of the upper and middle crust (Page et al. 1998). Based on the age of the Tulare formation, Page et. al. (1998) estimates an uplift rate of about 1.4 mm/year. The lack of major erosion within the relatively weak Franciscan formation may indicate that there has been recent uplift (Page et. al. 1998). The presence of uplifted marine terraces as young as .1 Ma suggest uplift could still be occurring and some geodetic surveys confirm this (Page et. al. 1998). Stream Power

A very important aspect of hillslope development is the amount of available stream power vs. the critical stream power threshold. Critical power as defined by Bull (1979) is the amount of stream power needed to transport the average sediment load. Above the threshold a stream will incise vertically into the hillside; below this threshold a stream will aggrade. Available stream power is determined by stream discharge and slope. Local climate and elevation above base level determine discharge and slope respectively. A change in climate would provide more or less water to an area. More precipitation increases discharge and available power and therefore the increases the ability of a stream to carry sediment load and downcut into a hillside. Inversely the opposite is true; less precipitation decreases discharge and available power. Uplifting the land drops base level, imparting more potential energy to the water and increasing the ability of a stream to carry sediment load and downcut into a hillside. Of course other variables are present such as stream roughness, sediment load, and vegetation; however, the dominant controls are climate and uplift.

Methods

This survey was conducted using a stereoscope and NAPP infrared aerial imagery. The IR imagery aided in distinguishing between vegetation and bare ground. Differences in cover were used for determining relative ages of landslides. In addition a field survey was completed to verify aerial findings. Landslides, stream terraces, and alluvial surfaces were recorded on the Maricopa and

Ballinger Canyon 7.5 minute USGS quadrangles reduced to 1:67,200 scale.

Results

Extensive landslide complexes and stream terraces were mapped (Fig 2, Append A). Landslides were recorded at the headwaters originating in the south and extending downstream to the north. Stream terraces were found within the alluvial surfaces in the north. The majority of the area is a very old landslide complex being distinguished from the surrounding landscape by its hummocky topography. Younger landslides cut into this older landslide complex. The youngest of the landslide deposits are located towards the headwaters with older landslides being found downstream.

Figure 2. Map Units and Descriptions

Discussion

The stream terraces within the Bitterwater creek watershed are all fill terraces. Unlike strath and cut-fill terraces which record a period of equilibrium, fill terraces represent the transition of stream power from below critical power to above (Bull 1990). Such transitions are thought to be climactic in origin (Bull 1990). Therefore, by dating the terrace deposits it is possible to link the terrace formation with climactic events. The rate of incision can also be determined by comparing the age of the terraces and their heights. It is important to note that because the terraces do not record a state of equilibrium, but only a cross over the critical power threshold, there will not be a synchronous age of all the terraces.

Throughout the watershed the shift in available stream power may have occurred at different times creating diachronous terraces within the watershed (Bull 1990). However, other local watersheds with similar geomorphic parameters may have synchronous terraces with the Bitterwater Creek allowing for more accurate timing of events (Bull 1990).

The landslides are mechanisms which compensate for rapid stream incision (Burbank et al

1996). This rapid incision suggests that there was a period of extreme storminess similar to what was described in Garcia’s and Mahan’s 2008 paper on Pancho Rico Valley. Whether or not these landslides were deposited within the valley will need to be investigated, providing clues to the amount of stream power.

Conclusion

Now that the stream terraces and landslides have been mapped it is possible to return to

Bitterwater creek to collect samples for dating purposes. Future studies done in this area can expand the understanding of hillslope development, specifically of the Coast Ranges and this region in particular. References

Bull, William B. 1990. Stream-terrace genesis: implications for soil development. In: P.L.K. Knuepfer a

nd L.D. McFadden (Editor), Soils and Landscape Evolution. Geomorphology, 3: 351-367.

Bull, William B. 1979. Threshold of critical power in streams: Geological Society of America Bulletin

v. 90 no. 5 p. 453-464.

Burbank, D. W., Leland, J., Fielding, E., Anderson, R. S., Brozovic, N., Reid, M. R., Duncan, C. 1996.

Bedrock incision, rock uplift and threshold hillslopes in the northwestern Himalayas: Nature

379, p. 505-510.

García, A. F., and Mahan, S. A., 2009. Sediment storage and transport in Pancho Rico Valley during and

after the Pleistocene-Holocene transition, Coast Ranges of central California (Monterey

County). Earth Surface Processes and Landforms, v. 34, p. 1136-1150.

Page, B.M., Coleman R.G., & Thompson, G.A. 1998. Late Cenozoic tectonics of the central and

southern Coast Ranges of California. Geological Society of America Bulletin v.110 no. 7 p.

846-876.

Pazzaglia, F.J., and Brandon, M.T. 2001. A fluvial record of long-term steady-state uplift and erosion

across the cascadia forearc high, western Washington State. American Journal of Science v. 301

April/May p. 385-431.