ABSTRACT 



This report covers the Coost Ranges province — a 30,000-sqJaremile area of coastal Coiifornio 

 between the Oregon border and the city of Ventura, nearly 600 miles southeast. To facilitate discussion 

 of the limestone, dolomite, and shell resources, this elongate province is divided into three regions — 

 northern, central, and southern. The deposits are grouped into 14 districts within these regions. 



The large population and high industrialization of the Son Francisco Boy area, located in the central 

 Coast Ranges region, has provided the moin stimulus for exploration and development, particularly 

 of the larger deposits. However, numerous small deposits of limestone, including some very impure 

 ones, have been developed locally as sources of lime and crushed stone for construction uses. 

 Altogether, roughly 100 deposits of limestone, dolomite, and shells have been developed commercially 

 in the Coast Ranges province. A diversity of carbonate materials has been used, including metamorphic 

 crystalline limestone and dolomite (Sur Series), fine, dense cherty limestone (Franciscan Formation), 

 Quaternary spring deposits (travertine, calcareous tufa, onyx marble, and coliche), late Quaternary 

 shells (San Francisco Boy mud), hard bioclastic limestone (Vaqueros Formation), and dense, impure, 

 bituminous dolomite (Monterey Formation), plus a variety of mostly impure sedimentary limestones 

 ranging in age from Jurassic to Quaternary. 



From 1850, when commercial production began, to 1968, an estimated 169 million tons of limestone, 

 dolomite, and shells were produced in the Coast Ranges province. Of this, more than 86 percent come 

 from the central Coast Ranges region around the Son Francisco Bay district, and almost all of the rest 

 came from the southern Coast Ranges region. Geologically, 37 percent of the production was limestone 

 from the Franciscan Formation; 32 percent was crystalline limestone and dolomite from the Sur Series 

 and similar metamorphic rock units; 19 percent was oyster shells from San Francisco Bay; 7 percent 

 was from Quaternary spring-associated deposits; and about 4 percent was from other formations. 



During the 1966-1968 period, there were 13 active operations at 1 1 different deposits and deposit 

 groups in the Coast Ranges. Eight of these operations were in the central region, and five were in 

 the southern region. The products were quarried and dredged and included: (1) limestone used for 

 cement, aggregate, rood base, riprap, building stone, decorative material, soil conditioning, livestocK 

 feed, beet sugar refining, and gloss manufacture; (2) shells used for cement, livestock feed, and soil 

 conditioning; and (3) dolomite used for refractory purposes, manufacture of magnesium compounds, 

 roofing and landscape rock, aggregate, road base, riprap, soil conditioning, marking athletic fields, 

 glass manufacture, whiting, and filter rock. 



Reserves of raw carbonate materials other than those associated with deposits currently under 

 development are fairly limited in distribution and kind. The northern Coast Ranges contain only minor 

 reserves of limestone. The central Coast Ranges contain moderate to lorge reserves of cherty Francis- 

 can limestone, crystalline limestone, and shells associated with boy mud; however, most of the better 

 quality and larger deposits are already under development. Limestone reserves of the southern Coast 

 Ranges region, particularly at the Pico Blanco deposit in Monterey County, ore very large. High-quality 

 crystalline dolomite in the southern region is present in modest but economically important amounts; 

 less pure dolomite of the Monterey Formation is much more extensive, but development has been 

 limited lorgely to aggregate and other construction uses. In spite of the obvious economic potential 

 of certain deposits in the Coast Ranges, development of several is severely limited because of 

 conflicting interests with urban, recreational, and wilderness developments and plans. 



