1978 



Limestone in the Coast Ranges 



33 



separated and stored for sale, but most of the material 

 is reduced in size by rolls or in a hammer mill to 

 obtain "fine" and "flour" products. The four sizes 

 (whole shell, half shell, fine, and tlour) are sold sepa- 

 ratel)' or combined as needed — mainly for poultry and 

 cattle feed. Some shell also is sold for chemical uses 

 and soil conditioning. The products are sacked and 

 shipped as far as Seattle. The shell products are mar- 

 keted as "Concstoga Brand Products" and guaranteed 

 to contain at least 94% calcium carbonate. Capacity of 

 the Petaiuma plant is not known, but it is reported 

 that approximately one barge-load (1,500 cubic yards) 

 of shells is processed each week. 



In addition to the shells processed in Petaiuma, 

 large amounts of washed shells are barged to the Ideal 

 Cement Company plant in Redwood (>ity to "sweet- 

 en" the Tiw materia! used to manufacture cement. 



References: Logon, 1947, p. 311; Davis ond Jennings, 1954, p. 407. 



South Bay Dredging Company. * This company is 

 owned by P.J. Gambetta (Route 1, Box 78, Brent- 

 \\ood), who has dredged shells from San Francisco 

 Bay since 195.? or earlier. He reportedly dredged south 

 of the Dumbarton Bridge prior to 1960 but, since then, 

 apparently has relocated to an unspecified area north 

 of the San Mateo Bridge causeway. Most of the pro- 

 duction since 1953 has been sold to Bay Shell Com- 

 pany (which see) for further processing and 

 marketing. I here is no record of production prior to 

 1953, although there is some indication that Gambetta 

 may have dredged shells at least as early as 1945 and 

 may have sold shells commercially. 



South Bay Dredging Company uses a self-propelled 

 suction dredge capable of operating in water as deep 

 as 10 or 1 1 feet. Dredging is done through two suction 

 pipes trailing aft while the dredge pushes a 1,000-cu- 

 bic-yard barge. Shells and associated mud are pumped 

 as a slurry into two separate trommels measuring 

 about 4 feet by 20 feet. Washing is effected by salt bay 

 water sprayed from an a.xial pipe running the length 

 of the trommel. Mud and fine shells are washed 

 through the '/g- or '/j-inch mesh trommel screen and 

 washed aft. The coarse shells are pumped as a salt 

 water slurry to the barge where water and some addi- 

 tional clay and silt arc allowed to drain from the shells 

 through screened openings. When loaded, the barge is 

 delivered via Alviso Slough to Alviso, where Bay Shell 

 Company purchases the entire production. 



The shells dredged probably occur as thin surficial 

 deposits associated with soft mud and distributed over 

 a large irregular area along the east side of the Bav (see 

 description above and figure 2). A chemical analysis 

 of the washed shells dredged by South Bay Dredging 

 Company shows 54.31% and 53.2% (^aO (samples 4 

 and 5, table 7). The shells arc somewhat broken and 

 slightly abraded, being a maximum of about 2 inches 



long. They are derived almost entirely from the native 

 oyster; but a small percentage consists of the Japanese 

 littleneck clam, bent-nose clam, bay mussel, and other 

 mollusks, some of which are dredged live. 



■ The company reported ic ceased iis shcll-dredging activities as of May 31. 

 1969 



Photo 5. Self-propelled dredge and barge of South Boy Dredging Com- 

 pony. Shells and mud were pumped from boy floor through two pipes oft {in 

 raised position) ond washed through two trommels before being pumped 

 through pipe (fore) into 1,000-cubic-yard copocity barge (left). Company 

 ceased operations in 1969. 



San Mateo Creek deposits. Location: Sec. 18, T. 4 

 S., R. 5 W., M.D., 3 miles southeast of Rockaway Beach 

 (Pacifica); San Mateo 15-minute quadrangle. Owner- 

 ship: City and County of San Francisco Water Depart- 

 ment (1962). 



Four discontinuous masses of Franciscan limestone, 

 extending 3,500 feet northwestward across the divide 

 between San Pedro and San Mateo Creeks, are shown 

 by Darrow (1963, plate 1). The largest mass has max- 

 imum dimensions of 1,000 feet by 350 feet and consists 

 largely of light-gray, dense limestone interbedded 

 with chert. The indicated size of this body is ques- 

 tioned because only scattered outcrops were observed 

 during a cursory examination in May 1962. Ho\Aever, 

 vegetation tends to obscure the extent of the deposit 

 and a positive evaluation was not possible. .According 

 to Darrow, there are several smaller limestone lenses 

 in sec. 20 a mile to the southeast. No quarries or other 

 improvements were seen, although Irelan (1888, p. 

 534) states that limestone occurs "at the headwaters of 

 San Mateo Creek, where lime was formerly burned." 



Skyline (Tyson) deposit. Location: S% cor. sec. 12 

 (proj), T. 5 S., R. 5 W., M.D., 5 miles west of Belmont, 

 San Mateo 15-minute quadrangle. Ownership: City 

 and (^)unty of San Francisco Water Department 

 (1964). 



I he Skyline deposit lies just west of Skyline Boule- 

 vard and half a mile southwest of the spillway of Crys- 

 tal Springs Reservoir. It is not certain when this 

 deposit was first opened, but W. O. Tyson (Logan, 

 1947, p. 309) wasoneof the early operators in 1945 and 

 1946. Although the operator in 1948 is not identified. 

 Walker (1950b, p. 7) reports that production at the 

 Skyline quarry was about 1,500 tons per day. From 



