The following is from a work-in-progress about the history of Fullerton. You can support my ongoing research and writing on Patreon.
“The earth is over 4 billion years old, but the oldest rocks in the county are less than 200 million years old. Thus, the geologic history recorded in the rocks found in Orange County only covers about 5% of the entire earth history! But, an amazing variety of changes to the landscape has occurred in that relatively short span of geologic time. We shifted plate boundary types, evolved through changing climates and organisms, emerged from the sea, and witnessed mountains to grow over a mile high!”
–Richard Lozinsky, Our Backyard Geology in Orange County, California
Not being a geologist, I rely upon the work of geologists to tell the story of Fullerton in time scales that are much larger and harder for humans to comprehend. We measure our lifetimes in decades. Geologists measure the Earth’s history in ages, eras, and epochs spanning millions of years.
Thankfully, I was guided on this journey by Fullerton College professor Richard Lozinsky, whose Earth Science class I took back around 2001. I found his class fascinating, as he used the rocks and landscapes of Orange County to teach us about geology concepts. We took field trips to places like Coyote Hills and Dana Point to learn about the stories rocks had to tell. A while back, I interviewed professor Lozinsky. You can read that HERE.
Recently, I re-read Lozinsky’s excellent book Our Backyard Geology in Orange County, California and so I present here a much simplified version of the local geologic story. For the sake of clarity (and my own comprehension), I am leaving out many technical terms and details.
About 200 million years ago, the supercontinent known as Pangea began breaking up into smaller plates. One of these new plates, the North American, began drifting westward.
About 29 million years ago, the North American Plate made contact with the Pacific Plate, and the two began a lateral (up-down movement) with the Pacific Plate moving upward. This created coastal depressions such as the Los Angeles Basin.
“Lands surrounding the basin began to emerge from the ocean forming a new coastline along the rising San Gabriel and Santa Ana Mountains. These new lands were relatively low lying and probably enjoyed a subtropical climate with rainfall amounts of 30-40 inches,” Lozinsky writes.
The marine life of the Los Angeles basin (like plankton) eventually died and formed the rich oil deposits that were discovered millions of years later.
“The ocean began its final retreat from the Orange County area about 5 million years ago when the convergence between the North American and Pacific plates intensified,” Lozinsky writes.
The San Andreas Fault Zone (SAFZ) formed at this time, and the Santa Ana river began to flow across the coastal zone, carrying sediment.
“By 1 million years ago,” Lozinsky writes, “the hills and mountains had almost reached their current elevations, defining the basin to look more like it does today. During the Pleistocene, the climate of the area was cooler and the landscape was grassland as indicated from the La Habra and Los Coyotes Formations. Here, sabre-tooth cat, giant ground sloth, dire wolf, horse, camel, bison, mammoth and mastodon roamed the region to eventually become extinct also.”
An excellent place to learn about this period is the Interpretive Center in Ralph B. Clark Regional Park, which contains fossils recovered locally of the above mentioned extinct creatures.
Over the next several thousand years, sea levels rose and fell as glaciers rose and melted.
“The present-day Orange County coastline was established about 10,000 years ago with the end of the Pleistocene. The earliest humans to visit our county probably came along the coast where food was more abundant,” Lozinsky writes.
Professor Lozinsky gives a glimpse into the future: “In the future, our coastline will slowly change as worldwide sea levels increase due to the melting of the polar ice caps and locally due to tectonic activity. Orange County will continue on its northwestward cruise towards Alaska as the Pacific Plate shifts with each earthquake that occurs along the SAFZ (San Andreas Fault Zone).”
Fullerton History 