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.

Authors hold full copyright ownership of their original works. Please contact the repository manager at digital@sdsu.edu for any further questions.

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Geology of the Gaudalupe River Gorge Area, Baja California, Mexico
At the Guadalupe River Gorge area in northern Baja California, five Ordovician-related allochthonous blocks, consisting of alternating metaquartzarenite and carbonate with subordinate hornfels, metasubarkoses and chert rests upon metasiltstones, metasandstones, metamudshales, phylli tes, and cherts of Mesozoic (?) age within a 4 square kilometer area. These distinct suites are separated by melange terrains which contain randomly oriented allochthon­derived blocks within an argillaceous matrix. All the metasediments are intruded by granitics and dikes of the Cretaceous Peninsular Ranges batholith. The metasediments possess a metamorphic grade no higher than green­schist facies and exhibit a strong westward dipping foli­ation within the argillaceous units. The entire terrain at Guadalupe has been litho­logically correlated to a strikingly similar terrain at San Marcos, 6kms to the north, which has previously been lithologically and paleontologically correlated to the Ordovician Valmy Formation of north central Nevada. Existing models suggest that roughly 800km of southward movement along a proposed Triassic to Jurassic "mega­shear" followed by the northward movement of the Neo­gene San Andreas Fault would place Valmy equivalent rocks at the general location of Guadalupe and San Marcos., San Diego State University
Geology of the Mesa Redonda area, Northwest Baja California, Mexico
The lfesa Redonda area includes about 34 square miles lying approximately 12 mi es south of Tijuana, Baja California. The rocks in the area range in age from Early Cretaceous to Quaternary. Two Cretaceous formations are present: the meta­volcanic Alisitos Formation and the Rosario Formation of interbedded sandstone and conglomerate. Plutons intruded the Alisitos during ¥.iddle Cretaceous. Prior to Tertiary deposition, a paleosol was developed on an irregular surface. Formation A, an =ocene marine mudstone, was deposited over the paleosol, followed by Formation B, a sandstone, and Formation C, a con­glomerate. Exact age of Tertiary ormation D, a basalt, is undeterminable., San Diego State University
Geology of the Santiago Peak Volcanics at San Miguel Mountain, San Diego County, California
The Santiago Peak Volcanics (SPY) is an elongate belt of volcanic and volcaniclastic rocks exposed along the western margin of the Peninsular Ranges batholith in Southern California. In the San Miguel mountain area exposures of the SPV are dominated by coarse-grained poorly bedded matrix supported lapilli tuff and breccia with lesser tuff and rhyolitic flow rock. These rocks have been statically recrystallized under greenschist facies conditions. The SPY here forms a NW striking NE dipping stratigraphic sequence that is cut by steeply dipping NNE striking cataclastic shear zones. This package is intruded by mid-Cretaceous granitic rocks of Pennisular Range batholith and unconformably overlain by Miocene Rosarito Beach Formation. Tilting of SPY and development of shear zones predates intrusion by granitic rocks. Lithologic characteristics and geometry of map units suggest emplacement on the flanks of an active volcanic center(s). A preliminary U-Pb zircon date from a rhyolite flow on San Miguel Mountain yields an Early Cretaceous age., San Diego State University
Geology of the migmatite exposures near Santa Ysabel, San Diego County, California
The migmatite exposures near Santa Ysabel, San Diego County, California, are pre-batholithic, and consist primarily of two rock types, tonalites and hornblende-biotite schists, with but minor biotite-bearing pegmatites. The area mapped consists of three exposures and encompasses approximately an area 375 by 375 feet. From the apparent geological evidence, the basic schistose feet. From the apparent geological evidence, the basic schistose dikes intrude the tonalites with sharply defined contacts, and in­trude earlier basic schistose dikes with less defined contacts. Xenoliths of basic rocks, in various stages of assimilation, and with some transaction by the basic dikes, occur in the tonalites; a few tonalite xenoliths are evident in the basic dikes. The schistosity of the dikes parallels the trend of the dikes and is controlled by flowage during emplacement of the dikes rather than by metamorphism. Polymetamorphism is apparent from the several generations of transecting intrusive basic dikes, and from the textures of the rocks displayed in thin sections., San Diego State University
Geology of the northwest portion of the Rancho Santa Fe quadrangle
The Santiago Peak Volcanics of Late Jurassic age are the oldest rocks exposed in the North­west portion of the Rancho Santa Fe quadrangle. There are more than 5000 feet of interbedded flows of andesite, basalt, agglomerate, brec­cia, tuff, and felsite exposed along strike normal stream beds. The origin of this ande­sitic sequence 1s thought to be from strong steam explosions of ultra-volcanian or Peleen volcanism whose source ls thought to be close by. Low grade metamorphism is indicated by the occurrence of epidote, chlorite, and pyro­phyllite. Joints are well developed in these highly indurated and locally silicified rocks. Two small northwest trending plutons of middle Cretaceous leucogranodiorite have intruded the older basement rocks. The granodiorite is fine grained, contains abundant mafic inclu­sions and is quarried in one locality as rip­rap. Flat lying Eocene sandstone unconformably over­lies the older meta-volcanic and granitic rocks. The sandstone is of marine origin and has been terraced by wave action. Stream gravels and conglomerates locally overlie the sandstone with unconformity., San Diego State University
Geology of the southern portion of the alpine quadrangle San Diego County, California
The mapped area in the southern part of the Alpine topographic quadrangle, San Diego County, California contains a few small roof pendants, batholithic rocks, and alluvium. The roof pendants are the oldest rocks in the area. One is composed of quartz-muscovite-silli­manite schist, containing dumortierite. Two others are composed of quartz-mica schist and quartzite. Exposures are mainly batholithic rock, probably of Cretaceous age. These, in order of decreasing age, are Cuyamaca Gabbro, Diorite, Green Valley Tonalite, Bonsall Tonalite, and Woodson Mountain Granodiorite, aplite and pegmatite dikes. Quat­ernary alluvium has been deposited in stream channels. The structural features include foliations, inclusions, and joints. The foliations were developed by the flowage of magma and appear near contacts and parallel to them. They are particularly pronounced in Green Valley Tonalite and Woodson Mountain Granodiorite in the north­west part of the area. Inclusions are abundant in tonalites and are believed to have been formed from gabbroic rock. They bear no preferred orientation. Joints are well-developed in Woodson Mountain Granodiorite striking north and northwest and dipping steeply. Dikes are numerous in all units and frequently strike in the same direction as joints. These primary structures together with the contacts of the batholithic rocks were useful in the determination of the intrusive sequence. The field evidence and petrographic studies indicate an origin from differentiated magma., San Diego State University
Geology of the western coyote mountains San Diego County, California
The western portion of the Coyote Mountains lies about fourteen miles west north west of Ocotillo in south western San Diego County. Late Paleozoic to Triassic schists and dolomitic marbles were faulted up against Cenozoic marine and non marine sediments of the Salton Basin by the Elsinore Fault during the late Pliocene or early Pleistocene. The throw of the Elsinore Fault is increased eastward by high angle distributive faults which meet the Elsinore at 30 to 40. A facies change of the canebrake conglomerate and the Palm Spring Formation is separated left laterally 1000 feet. Minor faults with the same sense as the Elsinoror related faults have cut terrace gravels developed after the major tectonic activity of the Elsinore Fault., San Diego State University
Geometrical analysis of a complex fold-fold fabric, Ocotillo Wells State Vehicular Recreation Area, SE California
Aerial photographs and Google Earth images clearly show that the Pliocene-Pleistocene sedimentary infill of the Salton Basin is complexly folded and faulted. However, little detail geometrical analyses of such structures have been completed. Hence, I undertook a detailed study of a complexly folded and faulted area lying east of Poleline Road in the Ocotillo Wells State Vehicular Recreation Area. Within the specific study area, in ascending order, the following three informal lithostratigraphic units were mapped: mudstone, interstratified mudstone and sandstone, and conglomerate. These units are folded about an EW trending anticline, and are cut by a high-angle reverse fault. These two structures define a high strain zone, bounded to the east by a NW striking dextral strike-slip fault zone, and to the west by several NE striking sinistral strike-slip faults, and imply NW shortening and EW extension during the development of the fold-fault fabric. Lying immediately to the north of the high strain zone is the Powerline syncline. A major dextral-reverse oblique-slip fault subdivides the syncline into EW and NW trending segments. In order to constrain the geometry of the Powerline syncline within these two segments, six cross-sections were constructed and labeled from east to west, A-A’ through F-F’. Along each cross section the geometry of the Powerline syncline was evaluated through a detailed stereonet analysis. The first step of this stage of my work was to plot and contour poles to bedding attitudes within each limb of the fold along each cross section. In each case, poles to bedding attitudes clustered in lower hemisphere equal area space, and as a result, an average of the cluster of points was used to define the attitude of each limb of the syncline. The resulting average attitudes of each limb were used to solve for the interlimb angle and the attitudes of hinge lines and axial surfaces along each of the six cross sections. This analysis indicated that the Powerline syncline varies from tight to open with interlimb angles varying from 60o -116o in EW trending segment. In contrast, in the NW trending segment it is open with interlimb angles varying from 128o-163o. In addition, in segments the syncline varies from gently plunging and upright to sub-horizontal plunging and upright. The general geometry of the fault/fold fabric within the study area is consistent with a maximum principal stress direction oriented ~NS while the minimum principal stress direction was oriented ~EW. The dextral-reverse oblique-slip fault that subdivides the Powerline syncline into two major domains, likely formed as a result of material being driven westward out of the high strain zone., San Diego State University
Geometry and morphology of cracks in saprock: Implications for ground shaking
Lying between the Elsinore and San Jacinto faults is a band of precariously balanced rocks first identified by J. Brune and colleagues. Peak accelerations during ground shaking events on the San Jacinto and Elsinore faults were shown by these investigators to reach minimal values about midway between the two faults. As a result ellipsoidal plutonic blocks (corestones), balanced on narrow pedestals of saprock connected to underlying bedrock, remain intact and extend above the land surface. In contrast, such precariously balanced rocks are generally absent at closer proximities to the faults, apparently a result of being knocked down during past ground shaking events. Several recent numerical models show that surrounding large‐slip strike‐slip fault zones is a large flower‐like envelope of damaged rock. Along the fault, this zone is generally narrow at depths but then widens significantly when traced to shallower depths reaching up to 10+ km at the land surface. Work by G.H. Girty, C. Replogle, and M. Maroun has shown that volumetric strains of saprock surrounding corestones within the band of precariously balanced rocks varies from ~0% to ~15%. However, at the few locations that have been studied adjacent to the Elsinore fault, volumetric strains range from ~26% to ~38%. Crack density analysis of saprock within ~14 km of the fault trace indicate that the formation of open and sealed cracks is likely a result of ground shaking. While there is a pronounced visible fracture fabric at each site, the microscopic open and sealed crack systems studied during this investigation show different orientations and thus are a result of a separate stress field. Data obtained during this study support the hypothesis that ground shaking due to fault rupturing is of sufficient strength to crack saprock and that microscopic open and sealed cracks may be indicators of such ground shaking intensity., San Diego State University
Geometry of Langford Well Lake Basin as estimated by gravity data, Fort Irwin, Southern California
A gravity survey was conducted at Langford Well Lake basin in Fort Irwin in Southern California to help determine the basement geometry. In the spring of 1996, a grid of field gravity data was collected in Langford Well Lake basin covering a 6 x 5 mile area. These data were collected and processed with the assistance of the United States Geological Survey and then compiled into a complete bouguer anomaly map. Three areas of the basin were then selected for modeling using a two dimensional gravity modeling computer program. All three sections were chosen to terminate on basement. The main section, A, is located in the middle of the basin, it mns northeast-southwest and crosses two negative gravity anomalies, the larger of which is centered on a dry lake bed, Langford Well Lake. This section was modeled using a typical density contrast between basement and the basin's sedimentary fill, then calibrated using preexisting well and seismic data. At the eastern end of Langford Well Lake the basement dips west at an angle of 21 degrees to a maximum depth of about 9 50 feet, and then gradually rises to the west until reaching the surface. An east-west cross section was created north of section A. This section, B, is asymmetrical, and, as in section A, shows the basement dipping fairly steeply on the eastern side but only to a depth of 250 feet. Section C was constructed on the west side of the study area and trends north-south. The interpretation of this cross section shows three sediment-filled channels which trend east-west between outcrops of basement. Sediments in the channels range in depth from 40 to 90 feet. The three cross sections give a reasonable idea of the basins sedimentary thickness, or the general geometry of the basin's basement., San Diego State University
Geophysical investigation of the Santa Margarita River San Diego, California using DC resistivity
The purpose of this investigation was to define the depth and nature of the Santa Margarita River basin in San Diego County California. The dc resistivity technique of geophysical investigation is well-suited to characterizing the depth and hydrogeologic nature of the saturated alluvial deposits because water is a good electrical conductor. Three dc resistivity soundings using the Schlumberger array were carried out along the west flank of the river. Survey #1 was conducted 30 m from the river; the results indicate a surface layer about 5 m thick with a resistivity of 45 ohm-m and a second layer about 24 m thick with a resistivity of 64 ohm-m. These two layers represent a saturated medium grained sand with varying silt and organic content. These conductive layers overlay a highly conductive clay-rich layer with a resistivity of 11 ohm-m. Survey #2 was conducted 70 m west of the river and parallel to survey #1. The results indicate a surface layer of dry sand with a resistivity of 24 70 ohm-m to a depth of 1. 3 m. Under this surface layer was a conductive zone about 22 m thick with a resistivity of 41 ohm-m representing a saturated silty sand layer. Underlying the conductive layer was a basement rock with a resistivity of 7600 ohm-m, representing a fractured granite. Survey #3 was conducted 100 m west of the river and parallel to the canyon wall. The results of the survey indicate a dry sandy surface layer about 1.4 m thick with a resistivity of 2370 ohm-m. The second layer was composed of sandy gravel about 15 m thick with a resistivity of 118 ohm-m overlying a resistive basement of fractured granite having a resistivity of 6000 ohm-m., San Diego State University
Geophysical mapping of San Diego River paleochannels within the San Diego Bay
High-resolution seismic data from within San Diego Bay was examined to identify faulting and ancient river drainages (paleochannels) of the San Diego River and Chollas Creek. These data revealed two fault zones, the Harbor Island fault zone and Spanish Bight fault zone, as well as numerous channel and delta features. The results of paleochannel and fault mapping indicate a relationship between the Spanish Bight fault and the past channels of the San Diego River, which used to empty into the Bay at the current site of the San Diego Airport. There is evidence of at least four channels following the trend of the Spanish Bight fault, suggesting that the channels were fault-controlled. The multiple channel system, may be indicative of an anastomosing river, which is different than the current San Diego River system that has undergone significant anthropogenic modifications. Alternatively, these channels may have been part of the San Diego River delta system where channels commonly bifurcate and change course. Studying the paleochannel network and its relationship to faulting will help geologists understand the broader hydrology and geomorphology of San Diego Bay. For example, these systems could be important for groundwater resources as they may act as fluid flow pathways in the subsurface., San Diego State University

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