58 



California Division of Mines and Geology 



Bull. 197 



Flint-Steinbeck deposit. Location; S'/z sec. 23, T. 

 13 S., R. 4 E., M.D., 4'/ miles south-southeast of San 

 Juan Bautista; San Juan Bautista and Hollister 15- 

 minute quadrangles. Ownership; Ideal Cement Com- 

 pany, 420 Ideal Cement Building, Denver, Colorado 

 80202 (1959). 



This deposit was a principal source of limestone 

 used in cement manufacture near San Juan Bautista in 

 the 1920s and 1940s. Limestone was produced from 

 quarries on both sides of a north-trending ridge and 

 transferred to the plant via a narrow gauge railroad. 

 The deposit has not been worked in recent years. 

 Since about 1950, the Bryan and Pearce-Twohy depos- 

 it, located 1'/; miles to the northeast, has been the 

 major source of limestone used at the plant. Bowen 

 and Gray ( 1959, p. 25) describe the deposit as follows; 



"Limestone occurs in a long thin lens, set on edge, the edge 

 trending N. 80° E. The sheetlike moss, tapered at both ends, dips 

 steeply south, has a traceable length of nearly 3,000 feet and on 

 average width of about 100 feet. It has been exposed to o max- 

 imum depth of 440 feet by erosion but probably continues below 

 the level of the adjacent canyon-bottoms. Wall rocks ore granite 

 and quartz-mica schist. The limestone is similar in physical charac- 

 ter and chemical content to the rock from the Bryan and Pearce- 

 Twohy properties. Considerable limestone remains in the lens but 

 recovery would be expensive because of the attitude of the mass 

 and because of the steepness of the topography. Much of the 

 remaining moteriol would have to be mined underground or else 

 stripped at high cost." 



Other references: Loizure, 1926, p. 226; logon 1947, p. 276. 



Fremont Peak deposit. Location: S'/, sec. 35 

 (proj.), T. 13 S., R. 4 E., M.D., about a quarter mile 

 south and east of Fremont Peak and 6/2 miles south- 

 southeast of San Juan Bautista; San Juan Bautista and 

 Hollister 15-minute quadrangles. Ownership; Reeves 

 Ranch and Bardin Ranch (1959). 



This deposit consists of four substantial masses of 

 medium- to coarse-crystalline, pale blue-gray lime- 

 stone grouped about the south flank of Fremont Peak. 

 These masses have been mapped and briefly described 

 by Bowen and Gray (1959, p. 31, plate 1), who esti- 

 mate the probable total reserves to be a million tons. 

 Three samples of representative limestone were 

 analyzed by L. A. Caetano of Ideal Cement Company. 

 The analyses are given below; 



Simple Sample Sample 



Oxide G^ G^ Gif 



CaO 55.02% 55.94% 55.52% 



MgO 0.69 1.53 0.46 



SiO, 1.58 0.42 0.14 



AljO, 0.58 0.08 0.17 



Fe,0, 0.30 0.08 0.13 



K,0 0.03 0.01 0.01 



Na.0 0.04 0.01 0.04 



Ignition loss 



(chiefly CO,) 42.14 43.62 43.60 



In addition to the main limestone deposits described 

 above, small masses of relatively pure dolomite and 

 limestone a short distance to the south and east have 

 been mapped by Bowen and Gray, some of which may 

 warrant future prospecting. 



Gamer-Harris deposits. Location; S'/ sec. 34 

 (pro).), T. 13 S., R. 5 E., M.D., three quarters of a mile 

 west of \'ineyard School and 6 miles south of Hollis- 

 ter; Hollister 15-minute quadrangle. Ownership; 

 Howard Harris, 7800 Cienega Road, Hollister, owns 

 the old Garner property west of Bonanza Gulch 

 (1962). 



Several medium-sized to small masses of crystalline 

 limestone lie on the north and east flanks of a 1,916- 

 foot hill (see geologic map, plate 2). The limestone 

 bodies, which are interbedded with schist and intrud- 

 ed by granitic rocks, generally trend west-northwest. 

 The limestone is typically medium to coarse crystal- 

 line, blue gray to off white, and frequently banded, 

 mottled, or brecciated. Some dolomite is present as 

 thin bands of near-white, medium-crystalline rock in 

 the limestone. Heavy soil, caliche, and vegetation ef- 

 fectively mask the extent of the deposits. However, 

 prospecting has helped to define the deposit bounda- 

 ries. 



Development of the deposits has been limited to 

 shallow prospect cuts and some stripping. A series of 

 137 samples, collected at regular intervals and 

 analyzed by the owner, indicate the deposits to be of 

 variable composition. Analyses, kindly furnished by 

 the owner, are given in table 13. Possibly 3 or 4 million 

 tons of limestone are present here, but much of this 

 would have to be mined selectively due to local con- 

 centrations of dolomite and granitic impurities. From 

 an economic viewpoint, the Garner-Harris deposits 

 would appear to be useful mainly as a reserve source 

 of cement raw material. Four of the larger deposits, 

 examined in October 1962, are discussed below. 



Big Flat deposit. This deposit is located in S'/jSE'/i 

 sec. 34, 3,000 feet southwest of Vineyard School. It is 

 pear-shaped in plan, with maximum dimensions of 

 800 feet by 500 feet and is exposed through 300 feet of 

 relief. A thick surficial layer of caliche masks much of 

 the lower part of the deposit, even where prospect cuts 

 exist. Where exposed, the limestone is light to dark 

 gray, medium crystalline, partly brecciated, and local- 

 ly siliceous. Some white, iron-stained dolomite exists 

 on the north side of the mass. In table 13 a series of 

 samples (BFA, BFB, BFC, BED), collected and 

 analyzed by the owner, indicate the limestone to be 

 low in MgO but to contain variable amounts of SiOj, 

 AljO,, and FejO,. Samples BE 1-16 represent the 

 chemical variations of the caliche. If the analyses are 

 representative of the deposit as a whole, use of the 

 limestone is probably limited to cement manufacture. 

 Reserves of limestone, including impurities and gra- 

 nitic dikes, are estimated to be no more than 18,000 

 tons per foot of depth. 



Dry Trough deposit. 1 he deposit is located in 

 SW'X sec. 34 (proj.), 4,500 feet west of Vineyard 

 School. It trends N 70° W and consists of limestone 

 and some dolomite exposed over an area having max- 

 imum dimensions of 1,300 feet by 400 feet with 250 



