1978 



Limestone in the Coast Ranges 



85 



typical limestone. Subordinate interbeds of gray to 

 buff, pebbly coquina, calcareous sandstone, and simi- 

 lar rock types constitute the less pure portions of the 

 deposit. .\ representative sample (Dubost # 1) of typi- 

 cal limestone from the main body was analyzed by 

 Lydia Lofgren of the Division of Mines and Geology 

 in 1962 and showed 51.4% CaO, nil MgO, 5.01% 

 SiOz, 0.5% AI2O3, 0.25% FeaOa, 0.05% P2O5, and 

 41. .H% ignition loss. 



The largest body of limestone underlies "hill 1905" 

 west of Camp Natoma (figure 7). The limestone, 

 which is almost continuously exposed over the crest 



and south side of the hill, extends over an elliptical 

 area half a mile long by a maximum of 900 feet wide. 

 .Most of the limestone appears to be relatively uni- 

 form, although two or three impure sandy and pebbly 

 beds were observed. The thickness of the body is not 

 known but probably is a minimum of 100 to 200 feet 

 to cover the hill so thoroughly. Limestone reserves are 

 estimated to be on the order of 120,000 tons per foot 

 of depth and may total 20,000,000 tons or more. Addi- 

 tional limestone, extending half a mile west of "hill 

 1905" to Franklin Creek, is reported by W. L. Stanton, 

 Jr. (1931, California Institute of Technology unpub- 



s Limestone [ vogueros Formation (Miocene) 

 sti Stiole J 



Jf Fronciscon Formation (Jurassic ?) 



Strike and dip of bedding 



?- Contacts 



-?- Faults 



, dost>ed wliere locoted approximately 

 queried wtiere inferred 



Figure 7. Geologic mop of Dubost limestone deposit. Son Luis Obispo County. 



