496 EMMONS AND MERRILL — SKETCH OP LOWER CALIFORNIA. 



The mesa east of San Diego bay is formed of strata carrying Pliocene 

 fossils, of which 69 species have been determined by Dall. Miocene 

 strata have not been positively recognized here, but they are distinctly 

 developed around the Santa Ana mountains, 100 miles to the north, and 

 from there extend westward to San Pedro hill, on the coast south of 

 Los Angeles, where they are partly covered by Pliocene and later beds 

 which surround the base of the hill. They are doubtfully recognized in 

 San Clemente, the southernmost of the Channel islands, and along the 

 coast southward from San Pedro are gradually replaced by the Eocene 

 (Tejon) beds, the relations between the two series not having been de- 

 termined. Miocene strata are also reported from the western border of 

 the Colorado desert, 70 miles east of San Diego, resting unconformably 

 on supposed lower Cretaceous strata. 



The upper portion of the " Mesa " is covered, according to Lawson, by 

 Pleistocene sands and gravels both of marine and of stream origin, which 

 extend to an average elevation of 800 feet above sealevel, marine post- 

 Pliocene fossils having been identified 12 miles from the coast. From 

 observations on the numerous terraces observed here and at other points 

 further north, both on the coast and in interior valleys, he deduces a 

 general depression of the region during Pliocene times and a post-Pliocene 

 and probably recent elevation of the continental margin from San Diego 

 to San Francisco of from 800 to 1,500 feet. 



At Ensenada, some 60 miles south of San Diego, Lindgren reports a 

 patch of coarse yellow sandstones and conglomerates in a protected angle 

 on the south side of Todos Santos bay, which have hitherto constituted 

 the southernmost known locality of the Chico-Cretaceous beds and 

 which carry fossils of the new genus Coralliochama considered character- 

 istic of the lower or Wallala division of this group. The beds dip 10° 

 to 20° to the northward, and are partially covered by post- Pliocene sands 

 and clays containing recent shells, which are also found at Sausal, on 

 the north side of the bay. He also recognizes several terraces and in- 

 distinct remains of beaches reaching a maximum elevation of 500 feet 

 above sealevel, indicating a recent elevation of the coast-line. 



Lindgren surmises, from the existence of sandstone cliffs at cape Col- 

 nett, 70 miles south of Todos Santos bay, and from the resemblance of 

 the mesa sandstones still further south, as described by Gabb, with the 

 Todos Santos occurrence, that the former will be found to be of Cretaceous 

 rather than of Miocene age, as Gabb somewhat doubtfully assumes. 



The section of the mountain region from Todos Santos eastward as 

 given by Lindgren is briefly as follows : The higher hills forming the 

 coast range to the north and south of Todos Santos bay are largely com- 

 posed of quartz-porphyrites and quartz -hornblende-porphyrites resting 



