Pebble Plains are a unique Ice Age-relict plant community found only in the Big Bear area of the San Bernardino Mountains. Consisting of many rare and endemic miniature plants growing on clay soils covered with orange quartzite pebbles, the pebble plains support a very specialized plant community that has adapted to these peculiar soil conditions.
During the Pleistocene Epoch (the Ice Ages)--beginning about 2.6 million years ago—Mt. San Gorgonio, just a few miles south of Big Bear Valley, was the southernmost peak on the Pacific Coast to have been glaciated. During glacial periods, Big Bear and environs was covered with a treeless alpine flora much like what one finds on Sierran peaks today. Then during warmer inter-glacial episodes, trees would climb higher on the mountain slopes, generally overtaking the alpine plants except on the clay soils. During winter months, the clays become saturated and freeze at night and thaw during the day. The freezing ice expands and then melts and contracts, the “frost heave” literally pushing the quartzite pebbles to the surface; then during summer months the clays become brick-hard and hot and dry, killing any pine seedlings. Thus, the pebble plains have remained as treeless openings in a sea of conifers to this day, harboring their alpine-relict species. The miniature plants of this area are both fascinating and fragile, with several of the plants federally listed as endangered or threatened species.
This sensitive habitat is very susceptible to high-impact recreational activities like off-road vehicles. To preserve these habitats for their unique ecological value organizations like the Inland Empire Resource Conservation District, San Bernardino Mountain Land Trust, U.S. Forest Service and other public and non-profit organizations have worked to safeguard these important habitats. For more information or to request a guided tour contact the California Native Plant Society’s Riverside/San Bernardino Chapter at email@example.com.
*Our Natural Resource and Outreach Teams would like to thank Dr. Krantz, professor at the University of Redlands, for his expertise and input for this article.