424 B. WILLIS — SOME COAST MIGRATIONS, CALIFORNIA 



turns eastward north of San Luis Obispo. A shorter range lies parallel 

 with and 10 to 15 miles east of the western. Between them is the double 

 valley of San Antonio and Nacimiento rivers. The eastern supports 

 Santa Lucia peak (5,967 feet), the highest in either range. In this article 

 it will be distinguished as the Santa Lucia Peak range. 



Having descended over the Miocene (?) sandstone and shale on the 

 eastern flank of the Santa Lucia range, the observer reaches the terraced 

 flats of the San Antonio valley. Strata outcropping here and there 

 through later gravels lie at low northeastern dips. East of the valley 

 rises the Santa Lucia Peak range, its foothills composed of white shale 

 characteristic of the Monterey (Miocene) formation. It also dips north- 

 east, overlying the upper sandstone of the Miocene (?) group. Imme- 

 diately east of the foothills rises the mass of the eastern range, composed 

 of the ancient coast complex. The structural relation of the Monterey 

 shale to these oldest rocks of the district forcibly suggests normal fault- 

 ing, but the fault was not demonstrated by observation of the contact. 



The course of the upper San Antonio valley is along the general strike 

 of the Miocene rocks. At a certain point, however, the stream turns 

 abruptly northeastward, flows through a short gorge in a low range of 

 hills, and, entering a broad valley, resumes its course southeastward. 

 The upper valle} 7 is opened in soft Miocene shale; the gorge is cut in 

 crystallines of the Coast complex ; the valley beyond it is developed in 

 shale and sandstone which are of lower Miocene (?) or Miocene age. 

 The basal member of the Miocene (?) group in this section is either 

 wanting or is much finer, much less conspicuously a conglomeratic sand- 

 stone than it is 3 or 4 miles farther west. The upper coarse sandstone 

 and conglomerate of the western outcrops also apjjears to be replaced by 

 shale in part, if not entirety. Widespread gravel deposits generally 

 obscure the strata in the lower San Antonio valley, but such outcrops as 

 were observed were of shale. This apparent change in sediments takes 

 place in a short distance (as is the case in a water body of moderate ex- 

 panse) and offshore from a land which lay to the west ; hence the in- 

 ference that the coarser Miocene (?) sediments were derived from a 

 western land beyond the crest of the Santa Lucia range. If so, that land 

 is now submerged beneath the Pacific. 



PINE MOUNTAIN SECTION ; FRANCISCAN TO PLIOCENE 



Where it was crossed in the vicinity of Cone peak the western Santa 

 Lucia range has been described as exhibiting Miocene (?) strata on the 

 eastern slope, rocks of the Coast complex in the summit and below on 

 the west, and Franciscan at the western base. Thirty-four miles south- 

 east of Cone peak the range was crossed a second time from Nacimiento 



