Big Bear Valley lies at the northeast end of the San Bernardino Mountains at an elevation of about 6,750 feet, surrounded by peaks of 7,000 to 10,000 feet. To the north and east the mountains drop abruptly to the Mojave Desert, yet just ten miles to the south looms Mt. San Gorgonio, the tallest peak in southern California at 11,502 feet.
During the Ice Age, some 18,000 to 20,000 years ago, Mt. San Gorgonio was the southernmost peak on the Pacific Coast to have glaciers. It was an ice-bound island. At that time the Big Bear area was covered by a large lake and around its treeless shores grew tufted, little alpine plants much like what one might find on Sierran peaks further to the north today.
As the climate became warmer and drier during the xerothermic period, about 8,000 to 10,000 years ago, the Mojave Desert expanded to the west, cutting off the San Bernardino Mountains from the Sierra Nevada by an arid expanse of over one hundred miles.
The Ice Age lake diminished until today Baldwin Lake is all that naturally remains (Big Bear Lake being a reservoir). The lake left a deep clay deposit, which persists, on the hill and beaches of Big Bear and Holcomb Valley. As the climate warmed, trees took over the higher mountain slopes, but the clay soils are too hot and dry in the summer months, making it difficult for pine seedlings to become established. Thus these areas have persisted to this day as treeless islands within a conifer sea, and it is on these openings that the alpine plants have survived.
Big Bear Valley’s geologic history and desert-montane climate have conspired to create the usual species diversity of this area. This diversity, combined with isolation from parent population in the Sierra Nevada have allowed natural selection to act on the plant populations, which have slowly evolved into unique varieties and species in themselves. The Serrano Indians were right about new species being created here!
The clay soil covered with ice age alpine plants and called “pebble plains” due to the layer of orange and white quartzite pebbles pushed to the surface of the clay by frost heaving. During winter months, sunny days cause the frozen surface to thaw. Then, at night, the ground refreezes, like ice cubes expanding in a tray that push on the surface cobbles forcing plants to float to the top.
Taken From: A Guide to the Rare and Unusual Wildflowers of the Big Bear Valley Preserve by Tim Krantz.
