78 SOUTHERN CALIFORNIA GEOLOGY 



tura Ranges and the ranges of the Piru Divide. Others, 

 the master highlands, are extensive, high-standing 

 fault blocks with plateau-like summits, and which con- 

 sist mostly of granitic and metamorphic rocks of deep- 

 seated origin. These blocks may represent the severed 

 and pushed-up parts of former, near-sea-level plains 

 (peneplains). The largest, highest and most exten- 

 sive of these master highlands in Southern California 

 are the San Gabriel, San Bernardino and San Jacinto 

 Highlands. 



These highlands have been little studied, classified or 

 described. Even today no suitable map of them as a 

 whole exists, except the small one herewith attempted. 

 (Plate 1.) And yet some of them, like the ones men- 

 tioned, are physiographic units of such striking indi- 

 viduality that, could they be set aside from their inter- 

 esting environments, each would prove a natural fea- 

 ture of greatest interest. 



In this paper I can give only an impression- 

 istic view. First I shall discuss them as consisting 

 of two major groups — not systems — which will be 

 called the Transverse and Peninsula Groups respect- 

 ively. Besides these groups there are several rela- 

 tively smaller individual features which stand alone, 

 such as the San Pedro Hill, some other isolated hills 

 along the borders of the sea, and the island groups 

 which project above the submerged, coastal shelf. 



Some of these highlands are simple domes or folds 

 of sedimentary strata such as the Dominguez and Ven- 

 tura Ranges ; others are tilted fault blocks of previous- 

 ly-folded sedimentary strata such as the Santa Monica 

 and Puente Ranges ; while still others are master high- 

 land blocks of granitic and metamorphic rocks 



