northwestern California and adjacent southwestern Oregon. The 

 mountains in this area are topographically rather rough, frequent- 

 ly accessible only with difficulty, and floristically very interest- 

 ing. There is a variety of soils in this area, including serpentine 

 and limestone, and because of this there is a relatively high num- 

 ber of plant species endemic to these moderately high mountains. 



4. Transverse Ranges: The Transverse Ranges consist of 

 relatively low mountains that run in an approximately east-west 

 direction in the southern one-fourth of the state. They extend 

 from near the Pacific Ocean eastward across the southern end of 

 the San Joaquin Valley and ultimately join with the southern 

 Sierra Nevada. 



5. Peninsular Ranges: This mountain system in the extreme 

 southwest section of the state is probably to be considered as a 

 southern extension of the South Coast Ranges, although the con- 

 tinuity is obscured by the intrusion of the Transverse Ranges dis- 

 cussed above. These mountains are relatively low, and like the 

 Sierra Nevada, offer extensive areas of granitic soils. 



6. Central Valley: This wide, flat valley occupies the central 

 portion of the state between the Coast Ranges and the Sierra- 

 Cascade axis. This valley is very flat and in some areas has exten- 

 sive marshes. Many of these have been drained for agricultural 

 purposes, but remnants still may be seen in various parts of the 

 valley. Before the development of intensive agriculture, the Cen- 

 tral Valley contained a number of interesting plant communities, 

 but these are now largely a thing of the past and we must rely on 

 historical records concerning their nature and extent. The soils 

 of the Central Valley are variable and may consist of peat, sands, 

 rich alluvial soils, alkaline clays, or rather sterile hard soils such 

 as those that occur in some of the oil-producing areas of the San 

 Joaquin Valley. 



7. Deserts: In the southern portion of the state and adjacent 

 regions there are two major deserts: 



A. The Colorado Desert: This is a low desert east of the 

 Peninsular Ranges that is presently dominated by the Salton 

 Sea. It extends into adjacent Mexico. 



36 



