Prehistoric San Diego County, Part 2

By Tom Oberbauer, CNPS-San Diego President


The cool west wind blew across the broad mesa several miles west of the dark pine covered ridge of what is now Point Loma. The vegetation was a mix of Artemisia californica (California sagebrush), Eriogonum fasciculatum (California buckwheat) and Eriogonum giganteum (Island buckwheat) and Ceanothus (wild lilac) shrubs, and prairie habitat. The grass was dominated by Stipa species but was blended with a lot of wildflowers, including butter yellow Layia platyglossa (Tidy tips), purple Castilleja spp. (Owl’s clover), blue and white Lupinus spp. (lupines) and the bright orange Eschscholzia californica (California poppy). The color of the flowers was brilliant under the hazy sun.  A herd of North American Stilt-legged llama grazed in the midst of the color, bending their long necks to feed on the grasses. They were more slender than modern Llamas in South America and built for speed. The afternoon breeze fluffed the fur of these animals as a couple of them stood holding their heads high, watching for predators.  Down the bluff below, the ocean swell created a dull roar and foamy spray.  

Steeler Sea Lion, Early T, U.S. Fish and Wildlife Service

On a dark, gravelly beach section, masses of Elephant seals that grow up to 4,500 pounds and 13 feet long lay flipping coarse sand on their backs and rolling in the surf. They were in the midst of Guadalupe fur seals, California sea lions and Steller sea lions, large, dark animals at 2,200 pounds (males) and 11 feet long that may be nearly three times the size of the California sea lion.  Large numbers of these massive animals were lounging on the beach below, barking and growling.  Sea otters floated and bobbed on their backs in the near shore water past the surf line. The offshore rocks were covered with roosting Cormorants, Brown pelicans, and Guillemots.  The rocks were white with guano, and the odor of bird colonies and pinnipeds drifted up the slopes that above were covered with brilliant yellow flowered Leptosyne gigantea (Giant coreopsis), its thick, succulent trunk providing its own prehistoric aura.  Shaded canyons above the ocean supported Lyonothamnus floribundus (Ironwood tree) with their scallop-edged dissected leaves and the dark needled Pinus muricata (Bishop pine).  

During the late Pleistocene, coastal San Diego County would have received roughly 20 inches of rain, much like modern day Monterey to the north. The coastal ridges and many terraces would have been vegetated with Pinus radiata (Monterey pine), Pinus torreyana (Torrey pine), Pinus muricata, and probably patches of Hesperocyparis forbesii (Tecate cypress) and Hesperocyparis macrocarpa (Monterey cypress). Chaparral would have grown in openings between the trees, on south facing slopes, and where the soil was not good enough for the trees, though these trees seem to thrive on poor soils. Most of Point Loma would have been covered with pines that extended northward through La Jolla and Mount Soledad and of course, Torrey Pines State Park and on past Carlsbad.  In addition to the north slope areas covered with trees, canyons off the side of the hills and the area around the intersection between SR-52 and I-5 would have also supported a mix of pines and chaparral, and oaks would have grown in the areas of San Clemente Canyon like they do today. Inland, pines and cypress trees also grew on many of the coastal mesas.  Vernal pools would have formed on the clay soils and hard sandstone.  The lower slopes and valleys such as the flats around San Diego, in what is now San Diego Bay and Coronado Island, would have had chaparral with various species of Arctostaphylos (manzanita) and Ceanothus (wild lilac) and a mix of scrub vegetation dominated by Artemisia spp. (sagebrush) and Eriogonum spp. (buckwheat), though at that time, only in the driest locations in contrast to the more widespread distribution in modern times. San Diego Bay itself would have existed as a shallow valley that supported Artemisia and Eriogonum in the low dry area that is in the rain shadow of Point Loma. The area around Chula Vista would have also supported mostly chaparral, but in especially favored locations conifers may have existed down the canyons much like a few Hesperocyparis forbesii do today, with riparian forest in the riverine portion of the valley.  Ceanothus pappillosus (Wartleaf Ceanothus) and Ceanothus thyrsiflorus (Buckbrush), both more common in Central California today, would have been growing on chaparral slopes. 

Stan Shebs, Hysperocyparis forbesii, CC BY-SA 3.0

Mira Mesa, Kearny Mesa, Rancho Santa Fe and on up to the mountains west of Escondido (Mount Whitney, San Marcos Mountains, Merriam Mountains) would have all supported mosaics of pines, Pinus muricataPinus attenuata (Knobcone pine), which would have been in areas of chaparral that burn, Pinus torreyana and Pinus radiata (Monterey Pine), Hesperocyparis forbesii and Hesperocyparis macrocarpa and chaparral. With more rain and clay soils, grasslands would also have occurred in patches and in valley bottoms. With the high diversity of closed cone species and chaparral, periodic fires would have occurred following dry periods as they do in Northern California today.

The wildlife diversity and variations based on fossils from La Brea and Anza-Borrego and other San Diego County locations would have been beyond imagination. There is little reason that any of the La Brea and Anza-Borrego fossils would not have occurred in San Diego County. Some of the animals are familiar to those of us interested in fossils, but the numbers of different large animals would have been extreme. There were two kinds of bison, a camel, llamas (as mentioned), and two kinds of horses (since camels and horses originally evolved in North America), a Shrub ox that was a bit like a large Musk ox and is thought to have been a browser on chaparral plants, Tapirs, two types of Pronghorns with one only 22 pounds, Elk, Mule deer, Bighorn sheep, Peccaries, a Mastodon, Columbia mammoth, and three species of large Sloths. These were just the herbivores. The carnivores included the Dire wolf, Timber wolf, Coyote, lion sized Saber tooth cat, Scimitar cat (with saber shaped teeth that was larger than the average lion and had heavy fore legs for grasping prey), American lion, Jaguar, Puma, Lynx, and American cheetah. The bears included the Giant short-faced bear, Black bear, and Grizzly bear. To scavenge and feed on the carnage resulting from the interaction of all of these animals, there were 6 types of eagles, 6 vultures including the giant Teratorn with a 12-foot wing span, and Caracaras. Other birds of note are Whooping crane, Turkey vulture, Clark’s nutcracker, Stellar’s jay, Pine siskin, Roseate spoonbill, and Pileated woodpecker. 

All these animals that have been found in various locations of southern California provide an indication of the vegetation and its productivity. The growth of shrubs and trees and grasses must have been extensive and rapid when considering the level of mammalian browsers and grazers. Considering the numbers of fossils that have been found, the types of predators and the level of prey that would be needed to support them, the numbers of wildlife would have been on the level of Ngorongoro Crater in Tanzania, Africa. They would have had an effect on the formation of the vegetation. While there are species that give the impression that the landscape supported open habitat, the presence of Pileated woodpeckers, Stellar’s Jays, Clark’s nutcrackers and Passenger pigeons indicate extensive forests of conifers, and oaks. Clark’s nutcrackers are now found in pine forests in the highest mountains, feeding primarily on pine seeds, and Pileated woodpeckers are inhabitants of large coniferous forests. Pine siskins are also indicators of forests; however, they are also migratory and during winter can sometimes be found in lowlands even today. But if they were only migratory, it would be very rare that they would be randomly stuck in the tar at La Brea. The Passenger pigeons that were so famous for flocks of millions of birds in hardwood forests in the eastern US, must have found large areas of favorable hardwood forests in the lowlands of Southern California, most likely dense oak forests. While turkeys may have existed here in the Pleistocene, they do not naturally occur here because they completely died out after the Pleistocene just as Mammoths and Horses did. The natural environment evolved after they were extinct here so that now their presence, since they have been introduced, is a threat to endangered butterflies and even oaks since they eat acorns necessary for reproduction in a modern environment of drought and oak killing Gold-spotted oak borer beetle.  

The presence of five-foot tall Whooping cranes is another indication of the habitat in the area since they both breed and winter in wetland areas with large expanses of standing water. They would have occurred in moist valley bottoms and in the broad edges of the major stream courses.

It is not clear if Redwoods extended into San Diego County but the precipitation here during the period of the La Brea tarpit fossils would have been very close to that of the Los Angeles Basin.  The vegetation would have been familiar at some level to Californians, though not for the San Diego area in modern times. However, the animals were like a combination of our normal North American mammals combined with a number from Africa, with the Giant ground sloth representing an animal seeming to be from a Star Wars planet.  

Imagine traveling up I-15 route from Mira Mesa through groves of pines, watching for Dire wolves that were very common and larger than the Gray wolf, and keeping an eye out for Saber-toothed cats. In the open valley where I-15 crosses the San Luis Rey River, herds of giant Bison that weighed nearly two and a half tons and had huge horns moved with the two types of horses and camels that were 7 feet tall at the shoulder.  Mammoths, Mastodons and Mule deer kept to the edge of the forests and woodlands, passing across openings in the trees, chaparral and scrub. Columbian mammoths grew more than three feet taller than African elephants and grew tusks that could be 16 feet long, five feet longer than an Elephant’s tusks.  Mastodons were a bit smaller than the African elephant though their tusks were formidable and in some cases longer than African elephants’ tusks. As mentioned, mammals that are still bewildering are the Giant ground sloth and its two relatives. The largest was a slow moving, massive animal with ossified skin that may have served as armor against the massive predators that existed at that time.  

In Pleistocene El Cajon Valley on a warm summer day, dawn broke as a herd of zebra horses grazed in a grassland on the dryer northwest side of the valley, toward where Santee is currently located. The area was rimmed with oaks, pines and cypress. A pride of lions eyed the herd, not far away but close enough to reach when the opportunity arose. The massive America lion could be 900 pounds, twice the size of an African lion. One Zebra in the herd seemed just a bit slower, leaning a bit to one side when it walked, suffering from an injured leg that broke through a Badger hole in an open grazing area. This was noted by the lions as they slowly spread out, working to isolate the weakened animal. Then suddenly, they made a trigger fast motion and charged the horses, dust flew and hooves thundered as the lions moved directly toward the weaker animal that was clearly not as fast. One female lion lept onto the horse’s neck and dragged it down. Condors and the larger predatory Teratorn vulture-like raptor joined in with other vultures that directed their flight to the scene of the attack.  

Down in the southern part of the valley near where Chase Avenue in El Cajon is currently located, a similar set of events were occurring only that time, the American cheetah chased down a Pronghorn. It is thought that the cat and Pronghorn co-evolved, each getting faster as natural selection limited the slower individuals.  

A Short-faced bear emerged from the shadows and moved slowly along the riparian woodland near the San Diego River, stopping to tear open a slope with pitch fork claws to devour Dichelostemma (Wild hyacinth) corms, digging up a gopher and grabbing a streamside estivating Arroyo toad that it unearthed. Short-faced bears, which were larger than the largest Grizzly, averaged 1,800 pounds but a maximum much heavier stood 12 feet tall and that could move much faster than a man were common. 

A small family of Columbia mammoths continued to feed, pulling branches off the Populus fremontii (Cottonwood) and Salix laseolepis (Arroyo willow) with their trunks and placing them into their mouths to grind them with their teeth. When darkness came, Dire and Timber wolves produced their mournful howl and Coyotes provided their yip-yip cries. Some Elk or Mule deer nearby were to be the target of the wolves in the waning light.  

At a settlement along the San Diego River, a group of huts made of bark, branches and tules (1) housed families of human inhabitants. These people had been here for many thousands of years (Deméré et al. 2017). Men with dogs, the dogs domesticated from wolves long before, stand watch on the outside to call alarm if a Short-faced bear came to the camp.  The main stream courses, the San Diego, Sweetwater, Otay, San Dieguito, and San Luis Rey, flowed long during the dry season with forests of willows, cottonwoods, White alder, and Box elders.  Steelhead trout that grew to nearly 40 inches in length inhabited the river water, returning to the sea after spawning.  Short-faced bears would have waded into the water to catch these silvery fish.  

Ceanothus verrucosus at San Diego Zoo Safari Park (formerly San Diego Wild Animal Park), Escondido, California, USA.

The north slopes around Mission Valley and the San Diego River Valley would also have supported conifers mixed with chaparral in the areas with Ceanothus verrucosus (Wart-stemmed ceanothus) and Quercus agrifolia (Coast live oak) in modern times. 

In what is now Camp Pendleton, a herd of hump-shouldered Ancient bison moved from their seasonal landscape, the ground rumbling beneath their hooves. They were followed by a pack of Dire wolves, waiting for a bison to stumble or show some indication of weakness before they charge.  Along the San Luis Rey River, a heavy muscled Smilodon (Saber-toothed cat) with powerful forelimbs has waited in the riparian vegetation for a mobile food source, which in this case was an Elk. Separate from its herd, it meandered along the edge of the open canopy following a Mammoth trail through the willows and cottonwoods. The Elk was unaware that a Saber-toothed cat, colored with spots and marks that blend with the shadows, was lying in wait for it to take just a few more steps before the cat leapt on the Elk’s back to deliver a fatal bite. 

Photographed and Copyright (c)2007 by John Kaufman, San Francisco, California, U.S.A., Wiki-llama, CC BY-SA 3.0

To support the massive predators like the American lion, Saber-toothed cats, American cheetah and both Dire and Timber Wolves, herd animals, Camels, Horses, Pronghorns, Llamas, Elk and Bison were necessary at high concentrations. As mentioned, browsing and grazing herd animals in those numbers would have affected the vegetation especially in valleys where grazing and browsing might have stimulated more grassland. Those grasses would have been dominated by Stipa and increased rainfall would have saturated wide areas of the soil to support herbaceous plants like Muhlenbergia rigens (Deergrass) rather than the woody shrubs. Even many of the forests and woodlands would have been open due to the heavy feeding by the Mammoths, Mastodons and Sloths. All of these animals would have needed continuous supplies of fresh water as an indication of the amount of moisture that must have been present all year.  The rainfall would have been predominantly during winter with a Mediterranean climate, but there must have been enough for permanent sources and wetlands to provide for large herds of herbivores and the associated carnivores.  There would have been a dynamic balance between the level of heavy natural browsing and grazing and the productivity of the vegetation. The high level of animal grazing and browsing may have created an environment where components of moist conditions such as coniferous forests are in close proximity in a mosaic pattern with chaparral and sage scrub components and low, marshy wetlands. The grazing may have created a false impression of aridity where the vegetation seems drier than it is due to the consumption by numerous large animals.


(1) Tules are grasslike perennial herbs which grow abundantly along the marshy areas of California. The term tule was derived from the Aztec tullin or tollin, which designated a grouping of plants including the common cattail, bulrushes, and similar plants. The term was used similarly by the Spanish to designate any such marshland plant.

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