1978 



Limestone in the Coast Ranges 



91 



18,000 tons per foot of depth at the southwest lens. 

 Assuming the lenses persist at depth, total reserves 

 recoverable by open pit mining may be on the order 

 of 15 to 20 million tons. 



Table 19. Chemical analyses of Novajo llmesfone deposit. 

 La Panza Range, San Luis Obispo County. 



Samples collected by Oliver E. Bowen. April 1959: 1-8 from main lens, 9 from 

 soulheast lens, 10-1 1 from southwest lens, analyzed by Pittsburgh Test- 

 ing Laboratory June II, 1959 



Based on the chemistry of the limestone, limited 

 reserves, and distance from transportation facilities 

 (30 miles by road to rail head at Santa Margarita), the 

 Navajo deposit appears to be useful, principally as an 

 emergency source of cement raw material. 



Newsom deposit. Sec. 23 or 24, T. 32 S., R. 13 E., 

 M.D., 2 to 3 miles east of Arroyo Grande; Arroyo 

 Grande IS-minute quadrangle. Ownership: Not deter- 

 mined. 



A flat-lying bed of soft, clayey limestone (marl), 5 

 to 6 feet thick, is reported in the canvon near Newsom 

 Springs (Aubury, 1906, p. 80; Logan, 1947, p. 306). 

 The material was burned for lime at a nearby kiln 

 around 1900 or earlier. The deposit apparently is too 

 small to be of economic interest. 



Nipomo deposit. Location: Near Nipomo. Own- 

 ership: Not determined. 



A large body of soft, marly limestone in the vicinity 

 of Nipomo is mentioned by Irelan ( 1888, p. .S32). The 

 deposit was developed as a source of lime in the 1880s. 

 The location and nature of this occurrence are not 

 known. 



Oak Flat deposit. Location: Not determined; re- 

 ported west of Paso Robles. Ownership: Not deter- 

 mined (1962). 



According to Angel (1890, p. 584), a bed of lime- 

 stone at Oak Flat was developed extensively as a 

 source of lime burned locally in the late 1880s. Al- 

 though Oak Flat is not identified on recent maps, it is 

 believed to refer to the low-lying granitic terrane 3 to 



5 miles northwest of Paso Robles (Jennings, 1958; 

 Durham, 1968). The exact location of the deposit is 

 not known. 



Other references: Aubury, 1906, p 80; Logon, 1947, p 306. 



Santa Margarita deposit. Location: Possibly sec. 5, 



6 or 8, T. 29 S., R. 13 E., M.D., 2 to 3 miles north of 



Santa Margarita; San Luis Obispo 1 5-minute quadran- 

 gle. Ownership: Not determined; probably Santa 

 Margarita Land and Cattle Company, 311 California 

 Street, San Francisco (1966). 



Brown crystalline limestone, exposed over a width 

 of 20 feet and length of 1 mile, is reported north of 

 Santa Margarita (Logan, 1919, p. 689). The limestone 

 is said to trend northwest. Detailed geologic mapping 

 by this writer in the area north of Santa Margarita 

 failed to reveal such a limestone deposit, although beds 

 of sandy algal limestone and fine-grained dolomite are 

 interbedded with punky calcareous mudstone and 

 shale of the Monterey Formation. These rocks do not 

 appear to be of economic interest, and none have been 

 quarried. 



Other references: Loiiure, 1925, p. 522; Logon, 1947, p. 306. 



Santa Margarita Ranch deposit. Location: Near 

 center sec. 28, T. 29 S., R. 13 E. (proj.), M.D., \% mile 

 southeast of Santa Margarita; San Luis Obispo 1 5- 

 minute quadrangle. Ownership: Santa Margarita 

 Land and Cattle Company, 31 1 California Street, San 

 Francisco (1966). 



Massive beds of sandy coquina and oyster shell reefs 

 as much as 10 or more feet thick are interbedded with 

 friable sandstone of the Santa Margarita Formation 

 (upper Miocene). The coquina is impure, consisting 

 of broken shell debris mixed with quartz-feldspar 

 sand. Entire shells of the giant oyster {Ostrea titan) 

 comprise the purer but less extensive reefs. The depos- 

 it is developed by a narrow bench cut about 200 feet 

 long with a maximum face of 12 feet, together with 

 several smaller prospect cuts and trenches in the im- 

 mediate vicinity. To the southwest and just below the 

 main cut is a concrete foundation — possibly the foun- 

 dation of a pre-existing crusher or other processing 

 facility. There is no record of commercial production, 

 although at least 1,000 tons of shells and sand were 

 quarried at the main cut. The deposit apparently was 

 prospected by (>omar Shell Company (Los Angeles), 

 whose lease on the property terminated about 1928 

 (1966, W. D. Reis, Santa Margarita Land and Cattle 

 Co., oral communication). 



Similar deposits of sandy coquina and oyster shell 

 reefs occur at various horizons within the Santa Mar- 

 garita Formation, elsewhere near Santa Margarita, 

 and in other parts of the upper Salinas N'alley. 



Tassajara deposit. Location: Sees. 21 and 28, T. 29 

 S., R. 12 E., M.D., 4'/, miles west of Santa Margarita; 

 San Luis Obispo 1 5-minute quadrangle. Ownership: 

 U.S. Forest Service land (1969). 



S. Aumaier of San Luis Obispo located three claims 

 on a deposit of white, coarse-crystalline calcitc prior 

 to 1925. The calcite occurs as veins, the largest being 

 12 to 14 feet wide, and was reported traceable over the 

 length of two claims (Laizure, 1925, p. 522). One 

 northwest-trending vein exposed by a small prospect 

 pit near N'/< cor. sec. 28 is reported to be 3 to 5 feet 

 thick and to consist of large, partly deformed crystals 



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