Topanga Canyon State Park where we will visit the chaparral is located in the transverse mountain range of Southern California.The transverse ranges are very unusual in that theyrun east to west. From east to west the transverse range includes theSan Bernadino mountains, the San Gabriel mountains and the SantaMonica Mountains. The orientation of the transverse range was createdas the Pacific Plate slowly rotated counterclockwise. This rotationnot only created the numerous faults and earthquakes for which thearea is famous, but it also created the transverse ranges themselves.These mountains are fault block mountains formed during periods ofsubduction. A dip-slip motion has resulted in the uplift of thesemountains. Most of this uplift has taken place in the last 2 millionyears.
The transverse mountains lie on the "big bend" of theSan Andreas fault. The active faults of the Los Angeles basin liebeneath the thick layer of alluvium that has built up over millionsof years from the floodwaters of the Los Angeles, San Gabriel andSanta Ana rivers. In the Santa Monica Mountains near Topanga you cansee many examples of the geologic history of this area.
The transverse and Peninsular Ranges tower around theLos Angeles floodbasin, which is only slightly above sea level. Someof the higher peaks are Mt. baldy in the San Gabriels at 3068 m, Mt.San Jacinto in the Peninsular mountains and the highest mountain inSouthern California, Mt. Greyback in the San Bernadino mountains at3506 m.
Fragile Habitats of Southern California is a part of LAEP Learning Exchange.