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Geoscience and technology > Geology of Camp Pendleton M.C.B.

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.


Remarks
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Camp Pendleton is a huge U.S. Marine Corps base situated on the Pacific Ocean in southern California. If not for it, urban development would have marched southward from San Clemente, Orange County, and northward from Oceanside, San Diego County, and knitted together. The result would have been the megalopolis of Santa-San: an uninterrupted urbanized corridor from Santa Barbara to San Diego, and obviously including L.A..

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

  • Enjoying the surf alongside the Marines and enjoying showers from a primitive beach-side shower head.

  • Studying my literature research and my mapping of the day beside a campfire.

  • Swimming in a tiny, isolated reservoir somewhere in the middle of the base.

  • Being awakened in the middle of the night by the half-eaten remains of a rat dropped beside my head by an owl.

  • Frustration the first couple days before the stratigraphy and its outcrop pattern became clear in Talega Canyon.

  • 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, given refuge for reasons unknown to me, which I came across on occasion.

  • Hauling 1½ gallons of water in a backpack every day of field mapping in the harsh summer of 1984.


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. See the Comparisons page.


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One must excuse the primitive methods used to prepare this document and its associated graphics for presentation. The text was written and edited on a primitive personal computer of the day (a Victor 9000; perhaps one resides in a museum somewhere). This thesis may have been one of the first developed using word-processing software. Access to a good printer was lacking back in 1985, so the final text product was typed on an IBM Selectric. Obviously, the photos were prints glued onto the pages, and all graphics were pen-and-ink. The digitized versions (2012) of Plates 1 and 2 leave much to be desired; better versions may be uploaded at a later date.

       Text of thesis           Plate 1, geologic map           Plate 2, stratigraphic column           Plate 3, cross sections

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