Week 6 Geological Interpretation
The county I chose to visit is San Diego County. I chose this county due to its complex geology. According to the California Geomorphic Provinces map, San Diego county incorporates mostly the Peninsular Ranges and a little bit of Colorado Desert, and Transverse Range. San Diego stretches from ocean to desert and can see a wide range in geological complexity without traveling very far.
Geologic Map of California
Starting on the coastline and then moving north-east we can discover quite a bit. Along the southernmost coastline budding up against Mexico to the south, we see Cenozoic marine sedimentary rocks. These rocks are made up of medium to fine-grained marine siltstone and sandstone layers.
Geologic Map of California
As we move north-east we see Mesozoic sedimentary and volcanic rocks in places strongly metamorphosed. This is where shale and sandstone were deposited in the ocean at a much earlier time. This is mixed with volcanic rock, much of which is basaltic volcanic pillow rock. It is called pillow rock due to the fact that it was the molten rock that reached the surface and most likely formed under water causing it to cool very quickly so it could not create any crystalline structures and was smooth and bulbous like a pillow.
Geologic Map of California
As we travel along our north-east path we can see Mesozoic Granitic rocks. These rocks were formed in a zone of melting that intersected both upper mantle and lower crust (Kistler, Peterman, 1973). These rocks cooled in the earth’s crust and later were exposed by erosion. You can tell this happened due to the extensive crystalline structures formed causing us to know that it cooled slowly. If it cooled quickly it would have not been able to have the time to create crystalline structures like the basaltic volcano pillow rocks.
Geologic Map of California
As we travel further we reach the corner of the San Diego county limits and the San Andres fault. This is where a few geomorphic provinces come together. Along with this San Andres fault line to the north-west, we see the Transverse Ranges. Due to the strong compression from the north and the south, the Transverse Ranges is one of the world’s most rapidly rising regions. This very thick rock area and it has been faulted and folded many times over. Due to the faulting and folding of these petroleum-rich sedimentary rocks, this is one of the United States most important oil-producing areas.
The things I would request to do aid in my interpretation would be any preexisting Geological relative dating time-scale map and Radiometric dating data. I would take this with an addition to the ability to take samples to measure chemical compounds found in the rocks along the various ranges. I would then compare them to the data already gained to compare and contrast in order to see if I can find any new cross-cutting sections to learn about any new and unfounded rock timelines. I would then give this to the USGS to be able to add as an understanding of this complex geological area.
Thank you,
Will
Resources:
GSA Bulletin (1973) 84 (11): 3489-3512.
Geologic Maps of California.
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