Posted on 03 June 2010.
Pretend you are walking down a path on campus and everything fades to black. The ground suddenly becomes moist, the wind picks up and debris falls from a canyon nearby. You open your eyes to a world 12,000 years ago. What would you see?
Botany, soil and geology experts say you would most likely be standing in a marshland. Tule elk by the thousands could be migrating nearby and mudslides would be much more frequent. These are only a few of the major players in a general consensus of what was characteristic in this time period.
San Luis Obispo 12,000 years ago was in the transition from one geological epoch to the next, from the Pleistocene to the Holocene. The Holocene is associated with the current warm period following the last glacial period, known as the last glacial maximum.
Antonio Garcia, a geology professor in the physics department said the biggest difference from the present was the lower sea level, sitting about 400 feet lower toward the end of the last glacial maximum, roughly 12,000 years ago.
The glaciers weighed the continent down, lowering the continent as whole, explained Brent Hallock, earth and soil sciences professor.
“We float on lava inside the earth,” Hallock said.
As temperatures rose, the glaciers began to retreat and the land mass rose up. This is known as the Isostatic rebound or post-glacial rebound, according to Hallock. He explained when visiting the current day shorelines at Montaña de Oro, “You can see some of the terraces as we rose up in elevation.”
Prior to the retreat, dune fields, also known as ergs, would consume places on the California coast like Montaña de Oro. These are characterized by little or no vegetation.
“Imagine the coast was much further out and then there was huge dune fields,” Garcia said. “They extended much further inland than they are today and there was actually dunes in Los Osos.”
These would have been similar to the Guadalupe dunes today. There’s a similar story for the Nipomo mesa and Santa Maria basin, which were formed by wind-blown silts.
“There was a dune field that extended from the coast, wherever that was, to past where (Highway) 101 is today,” Garcia said.
These are now the sea bottom where the continental shelf was flooded. As this rising process was happening, old stream beds were exposed, new stream beds were made and the coastline opened up.
“There was a lot more rainfall than there is today, almost for sure,” Garcia said. “The climate was generally wetter and much more stormy.”
Garcia said huge landslide deposits are evidence of this more turbulent climate and are as far south as the San Ardo area. Garcia’s research is looking at hill slopes with concavity by dating older sediments. The topic is well-studied further north in the Bay Area, but much of this research is untapped on the Central Coast. The studies indicate widespread landslide activity thousands of years ago.
Garcia also pointed out that the Cal Poly campus is most likely built on an alluvial fan (sediment deposits that fan out). This means if students were on campus 12,000 years ago, they might have been dodging debris flows from the nearby canyons.
San Luis Obispo and Laguna Lake area would probably look a lot like Morro Bay today, lowlands full of water. Atascadero was truly a big mud hole, representative of its name. Similarly, Arroyo Grande would have consisted of soft rocks with huge ditches and gullies, Hallock said.
Forests were more extensive and chaparral and coastal scrub were less abundant, according to David Keil, a biological sciences professor specializing in botany. The greater rainfall was more suitable for Bishop pine groves and similar large woodland areas. Cool season plants of Canada and the Pacific Northwest would have been more characteristic of the vegetation, Hallock said.
All the introduced plants would not exist, including eucalyptus, common weeds on roadsides and annual grasses from Eurasia. Keil said there would also be a greater proportion of wildflowers because of less competition from introduced grasses.
“The landscape would have been pretty colorful in the spring,” he said.
Streams flowing through would have created marshes and more local wetland communities. This also meant more Coast Live Oak woodlands and less in the way of shrub cover. The chaparral expanded at the expense of these woodlands.
There would have been streams with salmon runs and steelhead runs, Keil said. Grizzly bears would frequent the area as well as thousands of Tule Elk. The Chumash described one herd of Tule Elk, with thousands of individuals, taking days to walk by, Hallock said.
Goats, condors and eagles were other species that would dominate the area. At this time, deer were also starting to come in, Hallock said.
The oceans would have been more violent as well, according to Hallock, who found 11- to 13-inch Pismo clams at an archeological site on Highway 41 and Highway 1 in Morro Bay.
“The general distribution of mountains was about the same,” Garcia said.
The earliest known Native American settlements in San Luis Obispo County date back to 6500 BC, specifically Santa Margarita and Diablo Canyon area. About 9,000 years ago was the first settlement of Chumash Indians on the Central Coast. They were hunter-gatherers at the time, spending summers on the coast and moving East in the winters for shelter from storms.
From 8,000 to 4,000 years ago, dry climate expanded and deserts began to spread into their home range. Large bodies of water began disappearing. The streams prior to this period probably carried more water and the rate of evaporation might have been less, Keil said.
