Prehistoric SD County, Part 3

By Tom Oberbauer, Chapter President, CNPS-San Diego


The foothills and valleys in San Diego County would have exhibited even greater differences in vegetation from those of modern times. In addition to El Cajon, the major valleys, including Escondido and Ramona, would have supported low growing shrubs but also grassland due to increased precipitation and fine soils and the large numbers of herbivorous mammals.

Except for the big animals, the environment including the vegetation here would have modeled that of the inner mountain foothill slopes of the Monterey/Santa Cruz areas. Winter snow levels would have been repeatedly at 2,000 to 2,500 feet rather than the 3,500 feet that it is now. The foothill mountains, like Otay Mountain, Big Black Mountain, Mount Woodson, Viejas, Poser, Potrero and Tecate Peaks, were regularly snow-capped forested peaks following winter storms.

The vegetation on the foothill mountains would have been pines with Pinus coulteri (Coulter pine), more Hesperocyparis forbesii (Tecate cypress), Hesperocyparis stephensonii (Cuyamaca cypress) Pseudotsuaga macrocarpa (Big-coned Douglas fir) mixed with Quercus chrysolepis (Canyon live oak), and Quercus kelloggii (California black oak). Average precipitation on Otay Mountain would have been close to 40 inches. Acer macrophyllum (Big leaf maple) and Arbutus menziesii (Madrone) were also part of the forest vegetation community, the big leaves providing large yellow patches on the hillsides in the fall. However, Madrones were dark and grew with large shiny leaves and red bark. In the favorable locations with a bit more shade and rainfall, these trees would have also been mixed with Pinus lambertiana (Sugar pine), Pinus ponderosa (Ponderosa pine), Abies concolor (White fir), and Calocedrus decurrens (Incense cedar). This was the same type of forest that currently occurs near the top of the Cuyamaca Mountains and Palomar Mountain. In the hilly areas, Saber tooth cats, Jaguars, and Short-faced and Grizzly bears were common, preying on the Elk, Mule deer, and Bighorn sheep. Mastodons and sloths were individual food processors pulling down low hanging tree branches and shrubs in the forested areas, feeding machines that were actively engaged in eating through much of the day. Shrub oxen browsed on the chaparral and sage scrub vegetation, feeding and chewing for hours at a time, moving in small clusters and tilting their heavy horned heads at unexpected sounds. A Scimitar cat watched them from a shadowy vantage point.

Rainfall in Ramona, Escondido and Alpine would have reached over 30 inches on average as well with forests of oaks, Pinus coulteri, Pinus jeffreyi (Jeffrey pine) and Pseudotsuga macrocarpa. The hills east of El Cajon would have been covered with a mix of chaparral and woodlands of oak and pine. However, the vegetation would have been open on much of the slopes and river valleys interior basin valleys due to the high numbers of grazing and browsing mammals that were present in these locations, as well as low marshy habitats in the center of the valleys.

California Huckleberry (Vaccinium ovatum var saporosum) Photo by John Rusk

The hills north of Santee and near Mount Woodson were covered with pines and oaks mixed in the north again with Quercus kelloggii, the deciduous oak, turning rusty gold in the Fall. Celtis reticulata (Western huckleberry) and Acer macrophyllum would have also grown here with Calocedrus decurrens, Arbutus menziesii on north slopes in canyons and Umbellularia californica (Bay laurel) and Cercis occidentalis (Western redbud). Beneath the forests, Vaccinium ovatum (California huckleberry) grew as a major component of the vegetation. It would be difficult to say if Sequoia sempervirens (Redwood), the Thuja plicata (Red cedar) known from central California in modern times, and the Pseudotsuga menziesii (Douglas fir), were here. As mentioned, there are fossil indications from the trees of the La Brea tarpits that Redwoods were in the Los Angeles Basin. Douglas fir grows in small numbers in northern Santa Barbara County. If they weren’t actuallypresent in San Diego County at that time, they may have been close. The Redwoods may not have found conditions favorable enough for them since they thrive on coastal fog and high rainfall. While it would have been cooler, the coastal areas may not have had quite enough rainfall though they received some fog and in the interior the rainfall was greater but the fog was possibly less prevalent. However, there may have been certain hills such as the Santa Margarita Mountains that could have had enough rainfall and could have been an area where the fog settled with a cooler California current creating perhaps more fog. Case Springs in the Santa Margarita Mountains would have received more than 40 inches of precipitation in an area not as interior and therefore less likely to receive heavy snowfall and cold temperatures or dry periods but close to the coast to be affected by heavy fogs. It could have supported mixed evergreen forests with Maples, Oaks, Bay Laurel, Vaccinium ovatum and maybe, just maybe, some stunted groves of redwoods and Douglas fir.

Quaking Aspen (Populus tremuloides) Tewy, Aspen (Populus tremuloides) 02, CC BY-SA 3.0


The mountains were obviously subject to significant winter snowfall. The averages were higher until the prolonged drought of the last 20 years in which only 3 years were above normal. During the Pleistocene, snowfall on Palomar Mountain would have been over 100 inches per season and more than 160 inches per season on Mount Laguna, based on estimates of the mean level for those mountains in modern times that would have been more than doubled since a greater percentage of precipitation would have fallen as snow (Close et al. 1970). Average seasonal precipitation would be estimated to range from 50 inches on Mount Laguna to 65 at Cuyamaca Lake and 70 plus for parts of Palomar Mountain. While the original conditions would have been predominantly winter precipitation, summer monsoon rainfall would probably have also occurred in the mountain areas, particularly the Mount Laguna area. With colder mountains, the area around Cuyamaca would have looked different. Populus tremuloides (Quaking aspen) would have grown along the eastern edge of Cuyamaca Valley over to the desert slopes and would have spread down the east side of Mount Laguna with a continuous band extending down from the Santa Rosa Mountains, Santa Ysidro Mountains above Borrego Springs, and on the east side of Volcan Mountain. Pinus contorta (Lodgepole pine), Pinus lambertiana (Sugar pine), Abies concolor (White fir), Quercus kelloggi, Pinus Jeffreyi and Pinus ponderosa and Calocedrus decurrens (Incense cedar) would have all grown to the larger sizes in this area. On the upper slopes of Cuyamaca Peak, the precipitation would be approaching 80 inches with a lush, thick forest of conifers and probably more patches of Quaking aspen.

The view of Cuyamaca Lake would have been that of a broad, shallow lake that held water all year long. The east side of the lake would have had groves of fall yellow aspen with subalpine conifers to the west on Middle Peak and Stonewall Jackson Peak to the south.

Subalpine forest had many of the trees that were at the intermediate level forest around Cuyamaca Lake as well as a couple more, including Juniperus occidentalis (Western juniper), Pinus contorta ssp. murryana (Lodgepole pine), and Pinus flexilis (Limber pine), which is found just north of San Diego County now. Other interesting subalpine plants include Monardella species and Erythranthe purpureaus that grows in the San Bernardino Mountains around Big Bear Lake and the Sierra de San Pedro Martir. Douglas tree squirrels (Tamiascurrus douglasii) mentioned earlier, that is closely related to the Tamiascurrus mearnsii in the Sierra de San Pedro Martir, occupied the forests along with flying squirrels, Purple finches, Yellow-rumped warblers, and Red-breasted nuthatches. Ruby crowned kinglets with their strong warbling song were also flying around in the forests. Sooty grouse may have occurred in the higher elevations. The grating, hoarse call of the Clark’s nutcrackers would have been a common soundin the forest. Pileated woodpeckers, Lewis’swoodpeckers and white-headed woodpeckers would have been regular inhabitants in these areas as well.

Alpine Shooting Star (Dodecatheon alpine)

Sugar pines, White fir, Ponderosa pine and Hesperocyparis montana (San Pedro Martir cypress) were also present in the higher mountains but not quite to the highest elevations. The forest was dense and extensive. Mount Laguna was covered with aspen and subalpine coniferous forest. Laguna Lake was perennial, holding water all summer, and the forest extended to the edge of desert escarpment. However, what are now desert slopes would have also supported forests. The rest of the Laguna Meadow was an extensive subalpine meadow with Carex, Juncus and other wetland species including wildflowers like Iris missouriensis (Blue flag iris), Dodecatheon alpinum (Alpine shooting stars) and beautiful pink Lewisia brachycalyx (Short sepaled lewisia) and white-flowered Lewisia redivivum (Bitterroot).

Doane Valley and Mendenhall Valley would have had similar alpine and subalpine conditions. Volcan Mountain and the area around Julian had the subalpine vegetation but also deep forests. Hot Springs Mountain would have had subalpine as well on the slopes of its peak. Winter snow would have been extensive in the upper elevations, standing on the ridges and peaks for weeks at a time instead of just days as it does now.

The top of Cuyamaca Peak, the second highest point in San Diego County, would have been alpine or close to it, with Lodgepole pines, Aspen, Pinus flexilis and theSarcodes sanguinea (Snowplant) mixed at the level below the highest point. Similar to what is currently found near the top of the San Bernardino Mountains on top of Cuyamaca Peak and Hot Springs Mountain, there would have been an area of Alpine fell fields with Heuchera spp. (alum roots), Penstemon spp., and buckwheats (Eriogonum spp.).

On a walk out into the meadow in Mendenhall Valley on Palomar Mountain during a late winter evening one might have seen a few deer and a Puma skulking in the shadows of the massive 180-foot tall Sugar and Ponderosa pine trees. The Sugar pines had trunks more than 9 feet in diameter. On the nearby rocky ridge over on Eagle Crag on Agua Tibia Mountain, Bighorn sheep climbed up, pulling themselves through the chaparral and the adjacent woodlands. A lithe and graceful Jaguar watched them closely from the entrance of a rocky den nearby.

Banner photo: Big-coned Douglas Fir (Pseudotsuaga macrocarpa) Bigcone Douglas-fir at mtbaldy, CC BY 1.0