The last step in earning my master’s degree in geology was to submit a thesis. Its citation and abstract are as follows:
Citation
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Groffie, F.J., 1985, Geology and Late Cretaceous depositional environments in the northern corner of Camp Pendleton, southern California: M.S. thesis, San Diego State University, San Diego, California.
Abstract
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The main contributions of this thesis include (1) a detailed geologic map of the general geology of the northern corner of Camp Pendleton, (2) a model for the depositional environments of the Upper Cretaceous units, and (3) a better understanding of the Late Cretaceous paleography and relationships between the Upper Cretaceous units in Orange and San Diego Counties.
Methods used included geologic field mapping, section measuring, paleocurrent and conglomerate clast analysis, and sandstone thin-sectioning and grain-size analysis.
The study area contains a homoclinal and structurally intact sequence of Upper Cretaceous and Tertiary strata deposited on a Mesozoic basement complex. The Upper Cretaceous section has been subdivided into the Trabuco Formation, the Holz Shale Member of the Ladd Formation, and the Schulz Ranch Sandstone and Pleasants Sandstone Members of the Williams Formation. A Paleocene oxisol and the Eocene Santiago Formation overlie the Upper Cretaceous rocks. Extensional faulting is present in the study area. Sediments in the Upper Cretaceous units were derived from adjacent basement complex units and display characteristics typical of immature forearc basin sediments. Peleocurrents are bipolar (east-west) in the Upper Cretaceous marine sandstones and unipolar (west to southwest) in the fluvial sandstones and conglomerates. The Upper Cretaceous section is largely unfossiliferous, aside from plant fragments, common Ophiomorpha, and large angiosperm leaf impressions.
A transgressive fan-delta model is indicated for the Upper Cretaceous section. In this model, the fanglomerates of the Trubuco Formation toe directly into a marine environment. The Holz Shale and Schulz Ranch Sandstone Members record a complex interplay between braided stream, interdistributary bay, and beach foreshore environments. The Pleasants Sandstone Member contains turbidites and other rhythmically bedded sandstones deposited below wave base on a delta front. The presence of fanglomerates, plutonic and metamorphic sediments, and a transgressive sequence all imply a rapid downfaulting of the Late Cretaceous forearc basin in which these sediments were deposited. Significant differences distinguish the Upper Cretaceous Camp Pendleton sequence from strata of the same age in southern San Diego County. As a result, the Camp Pendleton section cannot be considered as transitional between the Upper Cretaceous Santa Ana Mountains and [southern] San Diego County sections, and few lithologic correlations can be made between the two districts.
The locality
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Camp Pendleton is a huge U.S. Marine Corps base situated on the Pacific Ocean in southern California. If the base hadn’t been there since 1942, urban development, beginning sometime in the mid-20th century, would have marched southward from San Clemente (Orange County) and northward from Oceanside (San Diego County) and knitted together to form a megalopolis. We might now be calling the resulting giant beast Santa-San: an uninterrupted urbanized corridor extending from Santa Barbara to San Diego, obviously including L.A.
Much of the base is essentially wilderness. In my study area, there were bulldozed roads to towers supporting electric power lines and a few other sketchy roads connecting one tiny valley to another. Otherwise, this was wild country.
Doing the field work
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Camp Pendleton contains a moderate level of development for military purposes along its valley-floor corridors. However, its rugged eastern portion and areas on the west are essentially wilderness. On most of my many days in the field, I decided against the 60-mile commute back to my apartment in San Diego and instead car-camped in the Camp Pendleton outback. I fondly recall
- Frustration on the first couple days in the field, in Talega Canyon, before the basic Cretaceous stratigraphy and its outcrop pattern there became clear.
- Being awakened in the middle of the night by the half-eaten remains of a rat dropped beside my head by an owl.
- Enjoying the Pacific Ocean surf alongside the Marines and enjoying showers from a primitive beach-side shower head.
- Studying my literature research and inking in my geologic mapping of the day beside a campfire.
- Swimming in a tiny, isolated reservoir somewhere in the middle of the base.
- Coaxing a young woman, another geology student who was working on the geology of a nearby area, to swim in the reservoir with me …
- … And she asking me to sleep with her in the bed of her small Toyota truck. She, as I did, wanted to avoid the commute back to the city, and I, for her, represented security. I shared with her my favorite campsite in Talega Canyon in the Camp Pendleton outback. She soon fell soundly asleep next to me in the bed of the truck. I, after suffering through a few cramped, sleepless hours, transferred down to the adjacent spacious forest floor to get a good night’s sleep.
- Climbing a steel stairway up into a range-control tower to discuss, with the range-control officers, whether it was safe to enter an area.
- Waiting for tanks to pass through San Mateo Canyon so I could do my field work there.
- The salute-to-civilians given by the soldiers as I passed through or past their guard stations.
- A small herd of bison, say twenty head, that was given refuge on the base for reasons unknown to me and that I came across on occasion, and, among them, a sad small calf with a broken leg that I spotted a few times.
- Hauling 1½ gallons of drinking water (warm) in a backpack on each of the many days of field mapping in the unusually hot summer of 1984.
- Heading off an attack by a small pack of large dogs, emerging from a cabin, evidently on privately owned land, by walking backward slowly, looking them in the eye, and pointing the butt of my long-wooden-handled rock hammer at them, ready to strike.
The geology is interesting. The sedimentary rocks record an interplay of onshore, beach, and offshore environments that received terrigenous sediments from igneous sources to the east, all of it associated with the North American–Pacific plate boundary. In the 1950s, oil was extracted nearby from one Cretaceous formation from depths of 4,000 to 6,000 ft.
I’m not inordinately beholden to everything in this thesis. Occasionally I think “what junk” when reviewing certain portions. Yet, I found it fascinating to compare my mapping with what later workers (who seemingly didn’t recognize work that came before) mapped.
Download the thesis: text and graphics
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Geologic map (plate 1), 11-Mb PDF