Collection Description

The Department of Geological Sciences has a long-standing Senior Thesis research option for the B.S. Degree which involves a written thesis, and a public oral presentation done under the supervision of a faculty member. These independent research projects typically involve field work and laboratory analyses of samples, but can also include laboratory-based experimental projects, numerical modeling of geologic phenomena and literature reviews. Senior theses are kept in the permanent collection of the Malcolm A. Love Library on the SDSU campus.

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VLF survey conducted at a proposed landfill site on the Campo Indian Reservation
On November 5, 1991 a VLF geophysical survey was performed on the Campo Indian Reservation, a proposed future landfill location, to determine the degree of subsurface and near-surface fracturing in the immediate vicinity of a pump and tracer test. The survey was performed along four 100 ft long parallel lines 10 ft apart trending N38E (perpendicular to the line between the pumping well and the injection well), and four 100 ft long parallel lines 10 ft apart trending N52W (parallel to the line between the pumping well and the injection well). Plotted data from this survey may indicate a series of fractures, or a fracture zone trending essentially northeast-southwest. Borings drilled at this location also indicate an intensely fractured zone near HG-31, the well used as our pumping well. Although a d.c. resistivity survey was to be performed to obtain a skin depth estimate, a combination of the site conditions and equipment problems prevented the survey from being performed. Since we were unable to obtain any data from our d.c. resistivity survey, it is not possible to estimate a skin depth with any degree of accuracy. Therefore, due to the complications in our VLF survey involving a barbed wire fence, the lack of a skin depth estimate, and an absence of reasonable anomalous trends, I would have to conclude that our survey did not penetrate into the underlying bedrock present at a depth of approximately 100-130 ft., San Diego State University
Visualizing topographical maps using Macromedia Flash 4.0: A tutorial for freshman and sophomore geology students
The Earth's surface, a complex 3-dimensional form, is commonly represented by 2-dimensional topographic maps. Undergraduates at the freshman and sophomore levels have a difficult time in going from 2-dimensions to 3-dimensions, and have difficulty understanding, interpreting, and locating features on topographic maps. In order to aid them in visualizing landforms that are depicted on maps, I constructed a web-based tutorial using Macromedia Flash 4.0 and Metacreations Ray Dream 5.5. I chose Macromedia Flash 4.0 because it is vector based and, as a result, complex 3-dimensional graphic files are kept small. Due to the ease of creating and manipulating 3-dimensional objects all ini6al graphics were completed first in Ray Dream, and then were imported into Flash where they were redrawn in vector form. Resulting vector-based Flash files are small, and commonly less than 100 KB, and are quickly downloadable to client computers.The resulting tutorial leads students through the development of topographic contours of simple landforms such as hillside slopes, ridges, valleys, and closed depressions. The tutorial terminates with a simplis6c, but elegant, example of how to construct a topographic profile., San Diego State University
Volumetric analysis of the Poway group alluvial fan, San Diego County, California
The Eocene Ballena Gravels supplied the Poway Group alluvial fan whose apex lies southwest of San Vicente Reservoir. The sediments extend east to west from San Vicente to Del Mar, and south to north from Lemon Grove to Rancho Santa Fe. No estimates of the volume of sediments in the Poway fan are available. Through extensive fieldwork and utilization of geologic maps, I determined 91 stratigraphic thicknesses to describe the fan. By establishing thicknesses on an x,y coordinate frame, I have analyzed these data using Dr. David Huntley'sContour program. This program draws contour lines at prescribed intervals and calculates a volume from the data points. The existing outcrop of Poway fan has a volume of about 16.5 km3 •, San Diego State University
Water on Mars: can magnetotellurics tell us?
There is renewed interest in Mars exploration particularly pertaining to the presence of water and it's implication for life. A model for the martian subsurface constructed by meteorite impacts, volcanism, and fluvial deposition suggests that liquid water could exist below a permanently frozen layer called the cryosphere. The resistivity of the liquid water layer would be much less than the dry surrounding layers creating a geoelectric profile seemingly ideal for magnetotelluric (MT) exploration. A highly anomalous magnetic field would probably not generate electromagnetic plane waves. Therefore, controlled source MT must be used to create the incident electromagnetic plane waves needed for the MT method. The quasistatic approximation required for MT only holds beyond -900 m depth for the model tested. Higher frequency for sensing depths less than 900 m would violate the quasistatic approximation. Computer simulation show that liquid water would be very detectable. Small changes in cryosphere thickness would not be detectable. Changes in salinity of the liquid water give the same apparent resistivity sounding as changes in thickness. No direct conclusions could be drawn about the thickness of the liquid water layer. The data could only provide a maximum thickness estimate., San Diego State University
What are the La Posta series soils: Paleosol or Mollisol?
The 1973 Soil Survey of San Diego County revealed a distintive soil series in the mountainous regions east of San Diego. Pedologists involved in the Soil Survey named it the La Pasta Series. The La Pasta series is characterized by the following horizons: R (unweathered granodiorite), Cr (weathered granodiorite), C (medium to coarse-grained loamy sand), A (medium to coarsed loamy sand with high organic content). Previous work by students at San Diego State University showed that the Cr- and C-horizons developed from the R horizon primarily as the result of plagioclase, and to a lesser extent K-feldspar, biotite, and hornblende weathering. However, the A horizon was poorly exposed at the initial study site and was not sampled. In order to assess how representative the previous work is of the mollisols that characterize the La Posta Series, an additional profile was sampled. The new profile was located ~30-40 m west of the earlier profile, and includes a well developed A horizon. New geochemical and petrological analyses indicate that the La Posta Series mollisols are composite, consisting of a paleosol (the R, Cr, and C horizons) and an overlying significantly younger soil (the A horizon) that formed under the modern day climatic regime., San Diego State University
Whole rock chemistry of the La Posta pluton, Peninsular Ranges, Southern California
The La Posta pluton is the largest mapped intrusion of the Peninsular Ranges batholith and covers an area of about 1600 km2 that stretches out from the U.S. side of the border into northern Baja California on the Mexican side of the border. Different models have been presented in order to explain how large volume granitoids bodies such as the La Posta pluton were generated and whether they were emplaced in a single magmatic event or over more than one event. The purpose of this project is to try and help constrain possible models for generation and emplacement of the La Posta pluton by studying compositional variation over large areas. In order to accomplish this task, two sets of samples from the La Posta pluton were collected. The set analyzed for this thesis came from the U.S. side of the border from along Old Hwy 80 and are relatively closely spaced. The second set came from the Mexican side of the border and are more widely spaced. Whole rock major and trace element concentrations were determined for all samples by X-Ray Fluorescence. The whole rock XRF data demonstrates significant regional variation in the composition of the La Posta pluton to the north and south of the International border. Samples to the nmih of the border range narrowly in Si02 content from ~65 to 71 weight percent and have consistently higher strontium contents than samples south of the border., San Diego State University
Whole rock geochemistry of the Peñasquitos Formation, San Diego County California
The Late Jurassic Peñasquitos Formation is a newly recognized formation in San Diego County distinct from the Cretaceous Santiago Peak Volcanics. The Peñasquitos Formation consists of low grade metamorphosed, volcanically derived, bedded sedimentary rocks that are exposed in five stream canyons throughout San Diego County: Los Peñasquitos Canyon, La Zanja Canyon, Circo Diegueno Canyon, Lusardi Canyon and San Dieguito Canyon. These are deep marine sedimentary and volcanic rocks based on the presence of the pelecypod Buchia piochii that were deposited by sediment gravity flows, including debris-flow, fluidized-flow, and grain-flow (Balch, et al.1984). Outcrops from three localities, Los Peñasquitos Canyon, Circo Diegueno and Lusardi Canyon were analyzed in this study. Whole rock major and trace element concentrations of volcanic breccias and sandstone from the Peñasquitos Formation determined by X-ray fluorescence show that most of these rocks are andesite and basaltic andesites that range narrowly from ~52 to 56 wt% SiO2. The rocks are subalkaline and low potassium corresponding to the island arc tholeiite series of volcanic rocks based on major elements. Concentrations of relatively immobile trace elements including Ti, V, and Zr similarly yield coherent patterns consistent with an island arc tholeiite affinity on various trace element discrimination diagrams., San Diego State University
Whole rock major and trace element chemistry of the La Posta pluton, Northern Baja, California, Mexico
The eastern portion of the Peninsular Ranges batholith (PRB) in San Diego County and northern Baja California is dominated by the La Posta pluton which is characterized by a relatively homogeneous composition of rocks broadly similar in composition to trondhjemite-tonalite-granodiorite (TTG) suites of Archean cratons (Kimbrough et al., 2001). The La Posta pluton has an enormous outcrop area and is divided into western (~ 1200 km2) and eastern (~400 km2) outcrops areas that were emplaced at different crystal depths, 2.3 ± 0.2 kbar and 4.7 ± 0.2 kbar, respectively (Symons et al., 2003). The purpose of this study is to determine whole rock major and trace element composition of widely spaced La Posta pluton samples to search for chemical variations and to see if the data can help distinguish between prevailing theories about emplacement of large continental margin batholiths. This study focused on the larger western "lobe" of the pluton in Baja California. This area was a prime choice due to its close proximity, good accessible outcrops, and lack of analytical data. Most work up to now has been done in the Southern California portion of the pluton. Forty-one samples were analyzed. There is significant compositional variation that may reflect different depths for the source of the magmas as well as shallow level crystal fractionation processes. The Baja California samples are also characterized by lower strontium contents relative to samples north of the border along Interstate 8 which suggest regional variations in the composition of the pluton not previously reported. Incremental filling of the magma chamber by separate batches of magma may be required. Local planar discontinuities in the pluton defined by differences in grain size and modal composition may reflect incremental emplacement of magma batches., San Diego State University
Whole rock major and trace element geochemistry from the northern part of the La Posta pluton, San Diego County, California
The La Posta pluton is part of a great chain of similar intrusions that form from the eastern side of the Peninsular Ranges batholith from San Jacinto to southern Baja California. The La Posta-type intrusions are big. Outcrop areas range mostly from 200 to 1400km2. Large intrusions such as these pose important questions about how the magma is generated and emplaced into the crust and over what time period. The purpose of this study is to investigate compositional variations within the La Posta pluton. The focus is an apparently homogeneous and distinct domain within the La Posta in the northern part of the intrusion between the Carrizo overlook along McCain Valley Rd extending north to Aqua Caliente and the Elsinore Fault zone. La Posta rocks here are homogeneous non-foliated and nearly free of mafic enclaves. Relative to outcrops immediately to the south, these rocks stand out at bouldery solid outcrops. The rocks also have a very consistent mineralogy and texture in hand sample. The rock is a medium grained leucocratic biotite tonalite/granodiorite. Accessory minerals are distinctive. Prismatic allanite crystals up to ~2cm in length are present in virtually every sample collected for this study. These are most easily spotted on big faces of rocks. Most of the samples for this study were collected in Bow Willow Canyon and Indian Valley. Strontium concentrations from these samples are uniformly high, around 600ppm. The distinctly higher Sr concentrations relative to other parts of the La Posta is consistent with the possibility that these rocks may represent a separate intrusive suite within the La Posta pluton. On the other hand, light rare earth element (LREE) concentrations within the sample suite are highly variable and span nearly the entire range of compositions displayed by samples around the entire La Posta pluton. LREEs are strongly concentrated in allanite. The variation in LREEs may be due to nonrepresentative whole rock powders which do no adequately account for allanite distributions in the rock., San Diego State University
Whole rock silica and trace element contents of volcanic and plutonic conglomerate clasts from the late Cretaceous Cabrillo formation, San Diego California: Implications for sedimentary provenance
Whole rock trace element analyses of conglomerate clasts from the Upper Cretaceous Cabrillo Formation were determined for 25 volcanic clasts and 6 granitoid clasts to investigate possible source areas for the clasts. Strontium, zirconium, rubidium, titanium and silica contents were analyzed by X-ray fluorescence done at San Diego State University and at Otago University in New Zealand. The average Sr contents for volcanics and granitoids were 113 and 180 ppm respectively. These concentrations overlap with those reported from the Santiago Peak Volcanics (SPV) and western zone plutonic rocks of the Peninsular Ranges batholith (PRB) and are much lower than typical values from eastern zone La Posta-type plutonic rocks of the PRB. Rubidium contents however are much higher than western zone plutons. Titanium concentrations are consistent when compared to SPV, but zirconium contents may distinguish the conglomerate clasts from SPV. This study is unable to confirm a close compositional similarity between Cabrillo Formation conglomerate clasts and PRB plutonic and volcanics suites exposed at the present erosional level., San Diego State University