30 



California Division of Mines and Geology 



Bull. 197 



ing for livestock feed and soil conditioning. (See com- 

 pany descriptions below for additional data.) 



Reserves of oyster shells are difficult to ascertain 

 with the data available. However, it is believed that at 

 least several tens of millions of tons of shells are avail- 

 able at a shallow depth (within 20 to 30 feet below the 

 bay bottom) east of the main ship channel in south 

 San Francisco Bay. Smaller reserves also veneer the 

 bay bottom in the same area. Shell deposits along the 

 San Mateo County shore and elsewhere in the bay are 

 probably small but may be of economic value. Some 

 of the deposits south of the Dumbarton Bridge and 

 along the San Mateo shore reportedly have been used 

 in the past. 



Economics 



The shell deposits of San Francisco Bay are actually 

 thin, low-grade, unconsolidated limestone deposits 

 that would be far less valuable (or even useless) if 

 located onshore. Some of the advantages enjoyed by 

 the shell operators include: 1) simple and inexpensive 

 mining by dredging; 2 ) ability to beneficiate the shells 

 inexpensively by washing with bay water; 3) use of 

 the mud impurities as a source of raw materials (alu- 

 mina, silica, iron oxide) in the manufacture of cement; 

 4) flexibility and low cost of transportation of 

 products within a large marketing area; and 5) low 

 land cost, especially for an urbanized region. 



1 he disadvantages associated with shell develop- 

 ment are not always obvious but generally relate to 

 multiple use and multiple jurisdiction of the Bay. 

 Manifold problems can develop when dredging, land 

 filling, shipping, sport and commercial fishing, and 

 various recreational activities are all carried on in 

 close proximity to one another. The varied activities 

 and different areas of the bay are managed by several 

 local government agencies, as well as by numerous 

 private land owners. 



Land ownership in south San Francisco Bay is com- 

 plex, and mineral rights to large areas are owned by 

 both public and private entities. The State of Califor- 

 nia owns most of the public land, but some land is held 

 by cities and other government jurisdictions. The 

 largest private owner. Ideal Cement Company, report- 

 edly controls about 30,000 acres of bay land between 

 Millbrae and Alviso. The approximate distribution of 

 lands owned by Ideal is indicated by Scott ( 1963, chart 

 opposite p. 4) as lands patented by the Surveyor Gen- 

 eral. An additional 4,730 acres of State-owned land is 

 leased by Ideal Cement Company for the purpose of 

 shell dredging. 



Shell Producers and Processors 



Bay Shell Company^. This company operates a 

 shell-processing plant at 37H() Lafayette Street, Alviso, 

 Santa (Mara County. Bay Shell (Company has proc- 

 essed oyster shells dredged from San Francisco Bay 



since 1924. During its early years, the company re- 

 portedly dredged shells from "near Alviso" (Logan, 

 1947, p. 311) and "a point about 2 % miles north of the 

 San Mateo drawbridge" (Davis and Jennings, 1954, p. 

 391 ) . In recent years, all of the shells processed by the 

 company were purchased from South Bay Dredging 

 Company (which see). Some shells also were pur- 

 chased from Beck Dredging Company (now Pioneer 

 Dredging Company) at least as early as 1946. Records 

 indicate that Bay Shell Company may have dredged 

 shells as late as 19.')6. The company was owned by 

 Santa Clara Sand and Gravel Company in 1962 and by 

 Steve Dorsa of Saratoga in 1967. 



When visited in 1962 and 1967, Bay Shell Company 

 received washed shells by barge at its plant on Alviso 

 Slough. Approximately four barge loads (capacity 1,- 

 000 cubic yards) per month were being delivered. The 

 shells are unloaded with a clamshell and conveyed to 

 a small gas-fired rotary kiln for drying. The dried 

 shells are sized over a multiple hummer screen having 

 openings of '/, inch to 10 mesh. A hammer mill is used 

 to produce finer sizes. Four sizes — whole shell, me- 

 dium, fine, and flour — are produced. These are sacked 

 separately or combined as desired. Most of the shell is 

 sold as poultry feed, but "flour" is sold for soil condi- 

 tioning and livestock. Based on the name of its prede- 

 cessor company — Agricultural Lime and Compost 

 Company — the products were marketed as ALCO 

 Products until recently. The products are now mar- 

 keted under the Bay Shell name. Chemical analyses by 

 Abbot A. Hanks, Inc., of two finished product samples 

 collected in 1967 showed an average content of .53.1% 

 CaO (see samples 6 and 7, table 7). Samples of washed, 

 but otherwise unprocessed, shells taken from the pri- 

 mary stockpile in 1962 and 1967 averaged 53.7% CaO 

 (see samples 4 and 5, table 7). Capacity of the plant 

 was 7 tons per hour, but this was expanded in late June 

 1962. Although the property is served by a spur of the 

 Southern Pacific Railroad, all products were being 

 trucked to market in 1967. 



The Bay Shell (-ompany plani ceased operations in lefts'. 



Photo 3. Boy Shell Company ptocessing plont at Alviso showing hopper 

 fot dredged and washed shells, conveyor belt, totary drier, screening tower, 

 and storage silos. Plant ceased operations in 1969. 



