prehistoric san diego county

Prehistoric SD County, Part 4

Prehistoric SD County, Part 4

By Tom Oberbauer, President CNPS-San Diego

During the Pleistocene, the San Diego County deserts would have looked very different. The coniferous forest would have grown far down slope onto the leeward side of the mountains into the upper deserts. Acer macrophyllum (Big leaf maple) grew in stands on the upper slopes. Lower down, Pinus monophylla (Single leaf pinyon) grew down to the desert floor near Blair Valley and Oriflamme Canyon.

Granite Mtn and the Pinyon Mtns not far from Earthquake Valley (aka Shelter Valley) as well as the slopes of the San Ysidro Mountains, and the slopes of Rabbit Peak northeast of Borrego near the San Diego/Riverside County Line were covered with coniferous forest of Pinus jeffreyi (Jeffrey pines), maybe some Pinus coulteri (Coulter pines), Quercus chrysolepis (Canyon live oak) and Juniperus occidentalis (Western junipers). Pinus flexilis (Limber pine) grew on Rabbit Peak. They were predominantly coniferous forest but the deciduous tree Quercus kelloggii (California black oak) would have also been found on the western parts.

Juniper woodland grew in Borrego Palm Canyon with 14 inches of precipitation per season. The Junipers occurred in groves around the perimeter of Borrego Valley except for the very sandy areas and the bottom of the Borrego Sink, the low point of the basin in the valley, that held water during winter and spring. Clark Lake was also full of water most of the year and was surrounded by Juniper and Pinyons. South toward Ocotillo and east toward Ocotillo Wells, the vegetation gradually dried and thinned. The Junipers dropped out to the east of Borrego Valley and near what is now the east County Line, the vegetation was semi-desert scrub with Larrea tridentata (Creosote bush) and Fouqueria splendens (Ocotillo). This vegetation would have existed on the eastern and southern edges of the County where rainfall was roughly 5-6 inches a season. The snow would have occasionally reached the desert floor. However, during summer, monsoonal moisture still occurred on the floor of the desert, augmenting the winter/spring rainfall.

Prehistoric SD County, Part 3

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) andArbutus 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.