34 



California Division of Mines and Geology 



Bull. 197 



about 1952 to early 1962, the operator was Skyline 

 Materials, Inc. (Howard E. Marks), of Belmont. That 

 company produced large amounts of crushed rock un- 

 til their lease expired. Reportedly, the City of San 

 Francisco considered the quarry operation a threat to 

 the quality of water stored for domestic use in Crystal 

 Springs Reservoir. 



The deposit consists of limestone and related rocks 

 of the Franciscan Formation. It is exposed over a 

 northwest-trending area at least 1,.'!00 feet long by a 

 maximum of .^.50 feet wide. Additional exposures of 

 limestone 1,500 and 3,000 feet to the northwest in sec. 

 12 may be a continuation of the deposit, but interven- 

 ing vegetation and soil cover prevent a definite corre- 

 lation. Weathered volcanic rock of the Franciscan 

 Formation flanks the deposit on both sides (Lawson, 

 1914, map; Davis, 1955, p. 437). Faulting has severely 

 crushed and disrupted the deposit, causing the rock to 

 be highly fractured and obscuring the structure. 



The limestone is typically of two basic types: 1) 

 light gray, fine grained, and foraminiferal; and 2) dark 

 blue gray, fine crystalline, and bituminous. Chert is 

 commonly interbedded but appears to be less preva- 

 lent than usual for Franciscan limestone deposits. One 

 representative sample of material collected from the 

 '/2-to 1-inch stockpile in 1962 contained 15 to 20% 

 chert. Greenstone and possibly other rock types are 

 present in small amounts as interbeds or in-faulted 

 material. The only available chemical analysis, from a 

 "70-foot part of the stratigraphic section", is given by 

 Walker (1950b, table 2) as 43.76% CaO, 0.29% MgO, 

 1.95% AI2O,, 0.33% Fe,0„ and 18.74% SiO^. Devel- 

 opment consists of a quarry perhaps 1,200 to 1,500 feet 

 long and 200 to 400 feet wide with a maximum face of 

 100 feet on the southwest and 30 feet on the northeast. 

 Operation of the quarry is described by Davis (1955, 

 p. 437-438) . The last operator. Skyline Materials, Inc., 

 produced crushed and screened rock mainly for road 

 base materials, bituminous and concrete aggregates, 

 and drain rock. In May 1962, the crushing-screening 

 plant was idle. Total production for the Skyline 

 deposit is probably close to 3 million tons. The extent 

 of the limestone reserves cannot be determined until 

 the depth and the continuity of the deposit to the 

 northwest are explored. 



Spring Valley Ridge deposits. Location: SE'^^ sec. 

 19 and E'/j sec. 29, T. 4 S., R. 5 W., M.D., 4 miles 

 southwest of Millbrae; San Mateo 15-minute quadran- 

 gle. Ownership: City and County of San Francisco 

 Water Department (1962). 



Darrow ( 1963, plate 1) shows several small- to mc- 

 dium-si/.ed lenses of Franciscan limestone along 

 Spring Valley Ridge. Most of the deposits lie at the 

 southeast end of the ridge near Pilarcitos Lake (Reser- 

 voir), mainly in E/2 sec. 29. The largest deposit here 

 is shown by Darrow to be a maximum of 1,200 feet 

 long by 4{)() feet wide. It consists of highly fractured 

 light- and dark-gray limestone with notable amounts 



of interbedded chert. It is exposed through at least 1 50 

 feet of relief at the top of the ridge and contains re- 

 serves of close to 30,000 tons of limestone and chert 

 per foot of depth. Several small limestone deposits 

 nearby have not been examined. Another deposit, cen- 

 tering in SE'X SE'/i sec. 19 about a mile to the north- 

 west, is situated just southwest of the ridge crest. 

 Darrow shows the deposit to be a lens half a mile long 

 by a maximum width of 300 feet. Only scattered lime- 

 stone debris was observed in the north part of the 

 indicated lens, and the deposit was not evaluated fur- 

 ther. 



The only development is a quarry with estimated 

 dimensions of 120 feet by 40 feet and a maximum 

 depth of 10 feet in the large lens in sec. 19. Approxi- 

 mately 2,000 tons of rock have been excavated recent- 

 ly, apparently by the San Francisco Water 

 Department as a local source of road material. 



Westvaco Chemical Division, Food Machinery and 

 Chemical Corporation (Westvaco Chlorine Products 

 Company; California Chemical Corporation) . This 

 company, now known as Inorganic Chemicals Divi- 

 sion, FMC Corporation, formerly (1931 to about 

 1950) purchased shells from Beck Dredging Company 

 (see Pioneer Shell Company) and manufactured lime 

 at Newark for chemical use and commercial sales (see 

 San Francisco Bay Shell deposits, FMC Corporation). 

 The company quarried dolomite for use in the produc- 

 tion of magnesium compounds at its Newark plant, 

 until that plant ceased operations in August 1968 (see 

 Westvaco deposit under Gabilan Range district). 



Wiedemann deposit. Location: SE'/, sec, 20 and 

 SWX sec. 21, T. 2 S., R. 1 W., M.D., V/^ miles south of 

 San Ramon; Livermore 15-minute quadrangle. Own- 

 ership: Fred Wiedemann, Norris Canyon Road, San 

 Ramon (1962). 



A 30- to 70-foot-thick lens of light-brown limestone 

 extending west-northwest over a length of a third of 

 a mile is reported on the northeast flank of Wiede- 

 mann Hill (Hall, 1958, p. 22, map). The west end of 

 this lens was examined in November 1962 and found 

 to consist of heavy beds of sandy coquina and fossilif- 

 erous sandstone. The beds are steeply dipping, up to 

 10 or 1 5 feet thick, and are interbedded with sandstone 

 of the Briones Formation (Miocene). The carbonate 

 rocks appear to be too impure to be of economic value. 



Unnamed deposit (near Sunol). Location: Sec. 

 22, 'F. 4 S., R. 1 E., M.D., 2'/; miles southeast of Sunol; 

 Livermore 15-minute quadrangle. Ownership: Not 

 determined. 



A large Pliocene "caliche" deposit is shown and 

 described by Hall (1958, map, figure 2) as a mappabic 

 unit a mile long by a third of a mile wide and as much 

 as 200 (?) feet thick. A smaller deposit also is shown to 

 the southeast. The "caliche" is described as white, 

 commonly containing yellowish-gray siliceous inclu- 

 sions. 



