Day 1: San Diego to Coalinga 320 Miles
The Bucket List Trip
So here we start June 5, 2021 San Diego California. A bit of irony as that there is no shortage of geologic wonders within a 3-4 hour drive of where we live: beaches, deserts, active fault lines, and exposures of rocks from a diverse set of ages. This trip we blow right past many of these places in favor of areas that have been "quiet" a much longer time, slow processes can sometimes reveal a new level of grandeur.
LA Basin
Some in our field are beginning to treat the freeways, skyscrapers, subdivisions, and sewers as geologic features and their models have plenty of natural analogues, but nothing moves quite as our species in these times. I am certainly not the first to think this . .
Crossing the San Andreas
It seems wrong to have only a paragraph or two of an Earth Science blog devoted to the San Andreas Fault and the Pacific North American Plate boundary. Like I've indicated these things are about 1/2 day's drive from us and thus can be explored on a long weekend. Many of our other destinations DO NOT fall in said category, and over the past year or so I've managed to document a good chunk of the San Andreas Fault Zone - so that material WILL find it's way somewhere.
It seems wrong to have only a paragraph or two of an Earth Science blog devoted to the San Andreas Fault and the Pacific North American Plate boundary. Like I've indicated these things are about 1/2 day's drive from us and thus can be explored on a long weekend. Many of our other destinations DO NOT fall in said category, and over the past year or so I've managed to document a good chunk of the San Andreas Fault Zone - so that material WILL find it's way somewhere.
On I-5, You Cross the San Andreas somewhere between the CA-138 interchange and Lebec. It's likely directly under the highway for the few miles in between. No sign, but if you look carefully you'll see a transition from poorly consolidated Sedimentary rocks to Igneous intrusive / Metamorphic Basement rocks. The Mountains rise up because we're on a left stepping bend of a right lateral fault and so the the stresses are obliquely compressional. Compression shortens and thickens the crust. The mountains bob up like a cork in water.
It Seems wrong to not to give a shout out to the Tehachapi Mountains here that rise up in Parallel to the Garlock Fault. The Garlock fault has an opposite sense of motion from the San Andreas, such that everything appears to move left. The Garlock San Andreas system can be thought of as a pair of conjugate joints forming an "X" that is getting squished from N-S while blocks of crust get squeezed out in the E-W directions. Nothing here is really solid. Today however we make it through earthwuake free
Following a dinner at Baja Fresh in Grapevine, we have ~ 2 hours left, The sky gets dark very slowly. Anita captures an absolutely epic sunset over the Southern Coast ranges. The Central Valley is of course famous for its agriculture. It's origins date back to a time when a now "lost" oceanic plate was subducting beneath a slightly skinnier North America. Sediment on the downgoing plate forms an offshore high that traps sediment eroding from the continent. Over the eons the deposits grow ever thicker giving rise to the "Great valley Sequence." These sediments are now exposed in the hills to our west, thanks to oblique compression on the San Andreas Fault and En Escehelon folding associated with more recent plate boundary stresses.
Many of the hills you see West of I-5 here are in fact Anticlines: folded packets of sediment shaped into into arches, whose axes run at an angle to the San Andreas fault. You can actually create these by shearing a layer of putty in a horizontal fashion. The alternating sequences of sediments of varying permeability led to some magnificent traps for the oil that formed from the organics in said sediment. While some of the anticlines are now eroded flat (Think "Lost Hills") at the surface the folded layers still show the same tilt in the subsurface and are mined for the hydrocarbons today
We Made Coalinga by ~ 930 and have been working on this blog before turning in. Until tomorrow.
enjoyed being on this road trip through the blog. Anita took an amazing photo of the sun set. I can tell exactly what is explained through the photos.
ReplyDeleteThis was super cool to read about! I enjoyed how you documented the different parts of your trip. Looking back at the post about the LA Basin, I agree that the area has geology written all over it. This is because there are many factors that play into geology; such as pollution, other natural disasters such as earthquakes of floods may occur, etc. Also, after reading the San Andreas Fault post, I noticed the mountains' landscape must be made from sedimentary or metamorphic rocks due to the weather. Also, the climate for San Andreas seems to be very dry and hot. I'm assuming there is high pressure in this region. Additionally, metamorphic rocks form when rocks are subjected to high pressure, which explains this rock in the San Andreas area! Overall, I enjoyed reading this blog and the sunset pictures look breathtaking! Thanks for sharing. :)
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