1978 



Limestone in the Coast Ranges 



69 



The rest of the calcined dolomite, some of u hich is 

 hydrated, is used extensivelv in several forms by the 

 chemical, building, and agricultural industries. 



Deadburned dolomite is produced by adding iron in 

 the form of mill scale to the dolomite feed and burning 

 at temperatures as high as .',U)0° F. This product is 

 shipped in bulk or bags for use as a fettling material 

 in electric and open hearth steel furnaces. 



Dolomite for roofing and landscape uses is selective- 

 ly quarried and processed separately in order to obtain 

 a uniformly white material. Crushed dolomite also is 

 sold to the steel industry for use in maintaining open- 

 hearth furnaces. In addition, dolomite fines from the 

 crushing plant are used for marking athletic fields and 

 for soil conditioning. Some of the waste material is 

 sold for use in road construction, and a small sand 

 plant was recently installed to process the waste fines. 



Production of dolomite (excluding waste rock) at 

 Natividad during the last decade has been between a 

 quarter- and a half-million tons annually. Total pro- 

 duction through 1968 is estimated to be approximately 

 8/4 million tons. Reserve figures are not available, but 

 based on the areal size of the deposit, dolomite re- 

 serves (including waste rock) may be on the order of 

 1 million tons per foot of depth. 



Other references, Allen, 1946, p. 68-72; Logon, 1947, p. 197, 256-257; 

 Bowen and Gray, 1959, p. 25; Hart, 1966b, p. 55-59. 



Palmtag-IIarris deposits. Location: SE'/ sec. 35, 

 SWVi sec. 36, T. 13 S., R. .S E., and NW'/, sec. 1, T. 14 

 S., R. 5 E., M.D., 6/2 miles south of Hollister and 

 immediately southwest of Cienega Road; Hollister 1 .'>- 

 minute quadrangle. Ownership: Howard Harris, 7800 

 Cienega Road, Hollister, owns the old Leopold Palm- 

 tag property (1962). 



The Palmtag-Harris deposits are situated on the 

 north and east sides of a 1,612-foot ridge partly defined 

 by Bonanza Gulch on the west and the San Andreas 

 fault zone on the northeast. The deposits include two 

 moderate-size masses (\'ineyard School, Hightop) 

 and several smaller ones (including Havfield) as in- 

 dicated on plate 2. However, soil, caliche, and vegeta- 

 tion effectively mask the deposits, except at the west 

 end of the \'ineyard School mass. Crystalline lime- 

 stone and subordinate dolomite constitute the depos- 

 its, which appear to be pendants in granodiorite. 

 Granitic dikes also cut the deposits in many places. 

 Brecciation and mixing of different rock types is com- 

 mon, the intensity increasing toward the San Andreas 

 fault zone. The limestone is blue gray to off white, 

 medium to coarse crystalline, faintly banded or brec- 

 ciated, and sometimes siliceous. Some off-white, me- 

 dium-crystalline dolomite was noted, particularly 

 along the ridge crest southeast of the 1,612-foot hill, 

 and may be present elsewhere. The chemistry of the 

 limestone is suggested by the analyses shown in table 

 14. The analyses shown by Bowen and Gray ( 1959, p. 

 36) for the Palmtag-Harris deposits are actually from 

 a deposit a mile to the northwest in NW'/^ sec. 34 



(proj.) (Oliver E. Bowen, 1963, personal communica- 

 tion). 



Limestone reserves probably amount to several mil- 

 lion tons. However, considering the variable quality 

 of the limestone, its main use would appear to be for 

 cement manufacture. Even so, some selective mining 

 would be necessary to avoid dolomitic zones and ex- 

 cessive siliceous or granitic material. The main advan- 

 tages of the limestone are that it is easily accessible and 

 close to other limestone deposits. Also, it is only 10 or 

 1 1 miles by road southeast of the cement plant near 

 San Juan Bautista. According to Laizure (1926, p. 

 254), some dolomite was quarried on the Palmtag 

 Ranch long ago, but the location of the quarry is not 

 known. 



The three deposit areas prospected and sampled in 

 recent years, mostly by the owner, are described in 

 additional detail below. 



Vineyard School deposit. This deposit is located 



a quarter of a mile southwest of \'ineyard School at 

 the northwest end of the ridge. It covers an east-trend- 

 ing, teardrop-shaped area with maximum dimensions 

 of 1,000 feet by 600 feet and a relief of about 200 feet. 

 The limestone is blue gray to white, medium to coarse 

 crystalline, and brecciated. No dolomite was ob- 

 served, but granitic salients commonly cut the deposit. 

 The only surface samples analyzed were obtained 

 from a bold ledge at the west end of the deposit. These 

 analyses (F-H-1 to 10, table 14) show the ledge to be 

 of relatively good quality. However, lower quality 

 limestone and the presence of numerous granitic dikes 

 are indicated in prospect cuts and drill holes made in 

 the 1950s by U.S. Steel Company. As drill data show 

 the deposit to extend to a depth of at least 180 feel, 

 limestone reserves, including granitic intrusives, are 

 estimated to be about 3 million tons. 



Hightop deposit. The deposit is located high on 

 the northeast side of the main ridge 2,000 feet south of 

 X'ineyard School. Although exposures are poor, pros- 

 pect cuts reveal the presence of carbonate rock over a 

 west-northwest-trending area about 1,600 feet long by 

 a maximum of 300 feet wide. Granitic rock also is 

 exposed in the cuts, and the deposit may consist of 

 several small masses. Most of the limestone is off white 

 to blue gray, medium to coarse crystalline, and faintly 

 banded. Some crystalline dolomite is present along the 

 southwest margin of the deposit, as well as farther 

 southeast along the ridge crest where no limestone 

 was observed. Analyses of 14 samples (see HT sam- 

 ples, table 14) indicate the limestone to be siliceous 

 and otherwise impure. The dolomite was not sampled 

 for analysis. More work is needed to determine the 

 quality and size of the deposit. 



Hayfield prospect. Small broken masses of lime- 

 stone lie in an area of low relief in the San Andreas 

 fault zone a third of a mile southeast of \'ineyard 

 School. These are poorly exposed but have been pros- 



