20 



California Dimsion of Mines and Geology 



Bull. i97 



is underlain by sandstone of the Panoche Formation 

 (Upper Cretaceous) which is locally overlain by the 

 Cierbo Formation (Miocene). A fossiliferous zone 

 containing abundant oysters .SO-to-l ."iO feet above the 

 base of the Cierbo is mentioned by Huey ( 1948, p. 41). 

 According to Ron Hart (personal communication, 

 1966), the Collins deposit is an impure shelly lime- 

 stone that caps a small knoll. It lies flat and is exposed 

 through a thickness of about 20 feet and over an area 

 about 100 feet across. 



Other references: Logan, 1947, p. 206; Davis, 1950, p. 343. 



Highway One deposit. Location: NW cor. sec. 1 1 

 (proj), T. 4 S., R. 6 W., M.D., in Pacifica, just south 

 of Rockaway Beach; San Mateo 1 .vminute quadrangle. 

 Ownership: Not determined (1962). 



A small body of typical light-gray, fine-grained, 

 thin-bedded limestone of the Franciscan Formation is 

 exposed on a knoll just east of State Highway 1. The 

 limestone contains interbeds of chert and appears to 

 grade locally into altered calcareous tuff(?). The stra- 

 ta, which are exposed over an area about 400 feet in 

 diameter, are complicated by faults and folds. Re- 

 serves are estimated to amount to 300,000 tons. 



The deposit is developed by a small quarry having 

 an area of 200 feet by 100 feet and a relief of 25 feet. 

 The use of the quarried rock is unknown, as the depos- 

 it has been idle for many years. Foundation remnants 

 at the deposit may have been for a crusher and other 

 processing equipment (see Eckel, 1933, p. 354). 



Other deposits, either smaller or less pure, lie near- 

 by to the east and southwest (Darrow, 1963, plate 1). 

 As these deposits are situated in a residential area, 

 their future potential as crushed rock sources would 

 seem to be quite limited. 



Hilltop deposit. Location: Near center sec. 1 1, T. 

 5 S., R. 5 W., M.D., 4'/, miles southwest of San Mateo; 

 San Mateo 15-minute quadrangle. Ownership: Gran- 

 ite Rock Company, P. O. Box 151, Watsonville (1964). 



This deposit consists of a sequence of Franciscan 

 limestone and chert beds just west of the crest of Ca- 

 hill Ridge. It is a northwest-trending mass which 

 crops out intermittently over an area 1,200 feet by 100 

 to 250 feet and is associated with greenstone and 

 vesicular basalt. The latter appears to overlie the lime- 

 stone. The beds are considerably crushed and broken 

 but appear to dip moderately southwest except at the 

 southeast end where they seem to dip gently 

 northeast. The limestone is light gray to dark blue- 

 gray, dense, fine grained, and thinly bedded. Thin 

 interbeds of dark chert occur throughout the deposit 

 and may constitute as much as 40% of the volume. A 

 chemical analysis of a sample representing a 35-foot- 

 thick section of "blue" rock shows 44.96% CaO, 0.36% 

 MgO, 2.23% AljO,, 0.5K% FcjO,, and 15.59%, SiO^ 

 (Walker, 1950b, p. 7, table 2). Walker indicates the 

 exposed thickness of limestone to be 55 feet. 



Just when development began is not known, but the 

 deposit was last quarried in 1951. In that year, the L. 

 C. Smith Company obtained crushed rock for use in 

 road construction in the city of San .Mateo. Two quar- 

 ry faces uere developed — the northwest face being 

 270 feet by 40 feet and the smaller southeast face 100 

 feet by 40 feet (Davis, 1955, p. 436). It is estimated that 

 50,000 to 100,000 tons of rock were excavated. The 

 deposit was acquired about 1963 by the present owner, 

 who drilled several inclined holes to assess potential 

 reserves. Limestone reportedly was encountered to an 

 inclined depth of at least 100 feet in one of the test 

 holes. Reserve figures are not available but probably 

 amount to several hundred thousand tons of rock. The 

 large amount of chert present probably limits the 

 deposit to structural (crushed rock) uses. 



Lime Ridge (Cowell) deposits. Location: Sees. 7, 

 8, 17, and 20 (proj.), T. 1 N., R. 1 W., M.D., 1 to 3'/j 

 miles southeast of Concord; Walnut Creek and Clay- 

 ton 7'/2-minute quadrangles. Ownership: .Main depos- 

 its — Newhall Land and Farming Company, 25 

 California Street, San Francisco; northwest deposits 

 (sec. 7) — L. R. and M. Ginochio(?), Antioch, and 

 possibly others (1962). 



Surficial deposits of travertine and calcareous tufa 

 on Lime Ridge were utilized extensively in the past 

 for cement, lime, sugar rock, flux, and soil condition- 

 ing. Initial development of the deposits may have been 

 by a man named Shreeve who worked the "Mt. Diablo 

 quarries" and burned lime near Pacheco (2 miles west 

 of Concord) in 1851 (Logan, 1947, p. 220). Early pro- 

 duction of limestone on Lime Ridge seems to be veri- 

 fied by Crawford (1896, p. 628). As records were not 

 kept prior to 1903, there is little information on early 

 development. 



From 1903 to 1915, Henry Cowell Lime Company 

 (since known as Henry Cowell Lime and Cement 

 Company) produced travertine for use in lime manu- 

 facture. The limestone was quarried at the main 

 deposits (probably in sec. 17) and shipped first to a 

 kiln in Concord and later to four continuous kilns 

 near the quarry (Davis and Goldman, 1958, p. 527). A 

 cement plant was constructed north of the main 

 deposits in 1907, and portland cement was produced 

 from 1908 to 1946. Travertine and calcareous tufa 

 from sec. 17 (proj.) and clay and sand from nearby 

 deposits were used as basic raw materials in cement 

 manufacture. Plant operations ceased in 1946 because 

 of the loss of rail facilities and the approaching deple- 

 tion of limestone reserves. The mill equipment was 

 sold in 1952, the main building being used as a ware- 

 house thereafter. Production capacity of the Cowell 

 cement plant was rated at 4,800 barrels of cement per 

 day. 



Spreckels Sugar Company also uorked the main 

 deposits on Lime Ridge for many years prior to 1915. 

 They quarried travertine south of the (>owell quarries 

 in N'/; sec. 20 (proj.) for use in beet sugar refining and 



