By Tom Oberbauer, Vice President CNPS-San Diego
The far northern part of San Diego County includes land that is north of Camp Pendleton under the ownership of the Cleveland National Forest. A portion of the Cleveland National Forest is the San Mateo Wilderness Area, a series of canyons including Devil’s Canyon. In Riverside County, several volcanic plateaus exist, including Mesa de Colorado and Mesa de Burro. These are volcanic plateaus consisting of a cap of volcanic rock that was laid down during the upper Miocene (8 million years ago, Kennedy 1977). The once continuous mesa formed by the volcanic flow was divided by erosion into a series of separate mesas. Nearly all of them are located in Riverside County, except one, Miller Mountain. The peak is 2,953 feet, with a mesa portion at 2,946 feet in elevation.
Another interesting fact is that the Santa Rosa Basalt volcanic rock is the home of Brodiaea santarosae (Santa Rosa Basalt brodiaea), a species that was described in 2007 (Chester, Armstrong and Madore 2007). It has characteristics that indicate it is clearly related to the federally threatened state Brodiaea filifolia (thread-leafed brodiaea), but it has longer flowers and grows bigger plus many have long filamentous staminodia but sometimes none at all.
The Brodiaea was one of the reasons that I have been interested in visiting the area, besides the fact that it is in a remote part of San Diego County that I have never seen.