54 



California Division of Mines and Geology 



Bull. i97 



appear to be of little economic interest because of size, 

 impurities, or poor accessibility. 



The limestone and dolomite deposits are discussed 

 alphabetically below by districts (plate IC). The dis- 

 tricts, which are discussed from north to south, are the 

 Gabilan Range, Panoche Hills, Northern Santa Lucia 

 Range, Parkfield-Coalinga, Southern Santa Lucia 

 Range, and Santa Ynez. 



GABILAN RANGE DISTRICT (C-1) 



Ihe Gabilan Range district is a 10-mile-wide moun- 

 tainous area that straddles the Monterey-San Benito 

 County boundary between the Salinas Valley on the 

 southwest and the San Andreas fault zone on the 

 northeast. It extends 45 miles southeastward from 

 U.S. Highway 101 to Topo Valley where it loses alti- 

 tude and gives way to the so-called Gabilan Mesa. 

 Although the Gabilan Range has a maximum eleva- 

 tion of only 3,454 feet at Mt. Johnson, much of it is 

 deeply eroded and rugged and accessibility is some- 

 what limited. Rail facilities are available to the north 

 at Hollister and San Juan Bautista and to the south- 

 west at various points in the Salinas \'alley. Limited 

 port facilities exist at Moss Landing on Monterey Bay 

 (plate IC). 



Pre-Tertiary crystalline rocks comprise the great 

 bulk of the Gabilan Range. The oldest rocks are schist, 

 gneiss, marble (limestone and dolomite), and quartz- 

 ite of the Sur Series of pre-Cretaceous age. During 

 Cretaceous (?) time, the Sur Series was extensively 

 invaded by granitic intrusives, and only scattered roof 

 pendants of the former remain — mainly in the north- 

 ern half of the range. The granitic rocks range in 

 composition from granite to quartz diorite but are 

 mainly quartz monzonite and granodiorite. Overlying 

 the crystalline rocks at the northern end of the range 

 is a highly faulted and folded sequence of sedimentary 

 and volcanic rocks of Oligocene to middle (?) Miocene 

 age. Included in this sequence are thick red beds, 

 breccias, and conglomerates of the \'aqueros Forma- 

 tion (lower Miocene) derived from the crystalline 

 rock complex (Allen, 1946). The southeast end of the 

 Gabilan Range is overlain by rhyolite flows and pyro- 

 clastics of Miocene age and various marine and non- 

 marine sedimentary units of Miocene age and 

 younger. 



Limestone and dolomite deposits of economic inter- 

 est are, with only one exception, restricted to pend- 

 ants of the Sur Series. The exception is the X'aqueros 

 Formation which contains thick red beds composed 

 largely of crystalline limestone rubble derived from 

 the Sur Series (see Barbee Ranch deposits). The gen- 

 eral distribution of carbonate rock is fairly well 

 known, although the extent and quality of many of the 

 deposits remain to be learned. As can be seen in plate 

 2, many of the carbonate pendants form linear groups 

 or belts that trend due west or northwest. Other 

 trends also exist, suggesting a complex history of fault- 

 ing and folding for the region. 



The numerous carbonate bodies of the northern 

 Gabilan Range consist of limestone, dolomite, and, 

 more commonly, mixtures of limestone and dolomite 

 (plate 2). Limestone tends to be more varied in its 

 characteristics than dolomite, ranging from fine to 

 exceedingly coarse crystalline and white to light and 

 dark shades of blue gray. The dolomite is generally 

 medium to coarse crystalline and white, cream or light 

 blue gray. Both types of rock occur in pure masses, 

 although dolomite often appears as replacement pat- 

 ches or bands in limestone. In many cases, carbonate 

 rock is penetrated by dikes and fingers of granitic rock 

 or is interleaved with schist and gneiss. Other deleteri- 

 ous materials associated with limestone and dolomite 

 include quartz in the form of veinlets and replacement 

 masses and silicate minerals developed in impure car- 

 bonate rock or adjacent to granitic contacts. 



The largest reserves of limestone are available at the 

 Bryan and Pearce-Twohy and the East Gabilan depos- 

 its, totaling an estimated 36 million tons. Ideal Cement 

 Company controls both deposits, the former being 

 worked until 1973 as a source of limestone for the 

 company's cement plant at San Juan Bautista. Lime- 

 stone reserves at the Upper Bird Creek, Blue Rock 

 Mountain, Garner-Harris, and Palmtag-Harris depos- 

 its possibly amount to several million tons each. Other 

 good-quality limestone deposits appear to be much 

 smaller, but may be useful for special purposes. The 

 Hamilton, A.S. and R., and Bardin Ranch deposits, for 

 example, may be useful sources for whiting and white 

 filler materials. 



The Natividad and Westvaco deposits, both actively 

 quarried as major sources of basic refractory raw 

 materials, probably are the largest pure dolomite 

 deposits in the Coast Ranges. Additional dolomite re- 

 serves are available at the Kaiser-Harris, Martin 

 Ranch, McCray Ranch, and possibly the Porter Ranch 

 deposits. 



Large quantities of mixed carbonate rocks and im- 

 pure limestone and dolomite exist in the Fremont 

 Peak and Natividad areas. The development of these 

 deposits, uithout the aid of beneficiation, appears to 

 be limited to crushed rock uses. Some of the areas 

 designated as "c" on plate 2 have not been examined 

 carefully and may contain useful reserves of limestone 

 or dolomite. 



The various deposits of the Gabilan Range district 

 are described alphabetically below. 



A. S. and R. deposit. Location: W'/j sec. 28 (proj.), 

 T. 1 3 S., R. 5 E., M.D., 5 miles south of Hollister at the 

 confluence of Bird Creek and North Canyon; Hollis- 

 ter 15-minute quadrangle. Ownership: Howard Har- 

 ris, 7800 Cienega Road, Hollister (1959). 



The deposit was held by American Smelting and 

 Refining Company for many years prior to 1947, but 

 it was never developed or even significantly prospect- 

 ed. The A. S. and R. deposit has been examined and 

 described by Bowen and Gray ( 1959, p. 31) as follows: 



