12 



"California Division of Mines and Geology 



Bull. i97 



manufacture in Contra Costa and Solano Counties, 

 but reserves are largely depleted. Some of the surficial 

 carbonate deposits, however, may be of value for orna- 

 mental uses. Quaternary shell deposits are of greater 

 future value, with apparent large reserves existing in 

 southern San Francisco Bay- The shells are largely 

 associated with soft bay mud which is used with the 

 shells for cement manufacture* or is easily washed 

 from the shells used for various agricultural and in- 

 dustrial purposes. Similar but smaller shell deposits 

 may also e.xist in the other bays and estuaries of the 

 central region. 



A variety of other limestone deposits, ranging in age 

 from Late Jurassic(?) to Pleistocene, have been used 

 or considered as sources of carbonate rock. Most of 

 these are too impure or too small to be of future inter- 

 est other than as local sources of crushed rock. 



Total production of limestone and shells in the cen- 

 tral Coast Ranges region through 1968 is estimated to 

 be H."! million tons. About 80% was used for cement, 

 4% for lime, 1 to 2% for livestock feed and soil condi- 

 tioning, and the remainder for aggregate, riprap, road 

 base, and other construction purposes. The principal 

 production has come from the following counties, list- 

 ed in approximate order of decreasing production: 

 Santa Clara, Santa Cruz, San Mateo, Contra Costa, 

 Alameda, Solano, and Napa. Minor amounts of lime- 

 stone have also been produced in Marin, Sonoma, and 

 San Joaquin Counties. 



The limestone deposits of the central Coast Ranges 

 region are shown on plate IB and are discussed below 

 in alphabetical order within each district. The dis- 

 tricts of the region are listed in geographic order from 

 north to south. 



HEALDSBURG DISTRICT (B-1) 



This district, which covers Sonoma County and 

 part of Napa County, is relatively unimportant as a 

 future limestone-producing area. Small amounts of 

 limestone were quarried intermittently as sources of 

 lime from the Black Ranch and Pope \'alley deposits, 

 and from an unnamed deposit near Geyserville, 

 between 1880 and 1937. Other deposits remain un- 

 developed. The only recent activity is at Petaluma, 

 where shells, dredged from San Francisco Bay by Pio- 

 neer Shell Company, are processed for livestock and 

 agricultural uses (see San Francisco Bay Shell depos- 

 its under San Francisco Bay district). 



Black Ranch deposit. Location: Approx. N'/2 sec. 

 30, T. 11 N., R. 9 W. (proj.), M.D., 5 miles north of 

 Geyserville; Kelseyville IS-minute quadrangle. (Own- 

 ership: Hollis M. Black, 28225 River Road, Cloverdale 



(1962). 



I his deposit has been worked mtcrinittently as a 

 source of lime rock from 1884 to 1907 and again in 



1937. According to Aubury ( 1906, p. 93 ) , "It was first 

 opened in 1884, and reopened in April, 1901" by the 

 Sonoma County Lime Company. The same company 

 worked the deposit again in 1906-1907. J. F. Bishop of 

 Santa Rosa apparently was the operator in 1937. 



The Black Ranch deposit consists of a single bold 

 outcrop of limestone l.'iO feet long by a maximum of 

 70 feet wide with a relief of about .SO feet. It lies 

 between the dirt access road and a west tributary to 

 Little Sulphur Creek. The limestone projects from a 

 structurally disturbed terrain mainly consisting of 

 graywacke, chert, schist, greenstone, and other Fran- 

 ciscan-like rocks. Faint bedding(?) in the limestone 

 appears to dip steeply to the east. The limestone is fine 

 to medium crystalline, dense, brownish gray some- 

 times mottled with white, with no visible impurities. 

 Two typical grab-samples (BR-1 mottled with white) 

 were analyzed by Lydia Lofgren in 1962 and show the 

 following chemistry: 



Sample 



CaO MgO SiO: AJ,0, Fe,0, P,0, 



Ign. 

 loss 



BR-1 

 BR.2 



55.00% 0.45% 0.80% 0.12% 0.07%o 0.04% 4?.08% 

 54..50 1.19 0.90 0,13 0,14 0.02 43,22 



' Production of shells for ccnicm nianufaclurc ceased in late 1970. Sec foot- 

 notes under San Francisco Bay Shell deposits 



Development is limited to a small hillside quarry on 

 the north side of the deposit. Not more than a few 

 thousand tons of limestone were quarried, and this 

 was hauled 300 feet east to a vertical (continuous) 

 stone kiln of .50 barrels per day capacity. Reserves are 

 small; probably not more than 20,000 to 30,000 tons of 

 limestone. 



Other references: lrelan(?), 1888, p. 633; Crawford, 1894, p. 396; Brad- 

 ley, 1916, p. 323; Logan, 1947, p. 333; Honke and Ver Planck, 1950, p. 95. 



Healdsburg Marble Company deposit. Location: 

 NE'X sec. 2, F. 9 N., R. 12 W., M.D., 7 miles west- 

 southwest of Skaggs Springs and 15 miles west of 

 Healdsburg; Tombs Creek 7'/2-minute quadrangle. 

 Ownership; Not determined. 



Many years ago, a company by this name located 

 claims on a fine-grained, "red, white, and cream col- 

 ored" limestone in sees. 1 and 2 (Bradley, 1916, p. 

 323). Fhis undoubtedly is the same as, or includes, the 

 reddish Franciscan limestone at the southeast end of 

 Shoeheart Ridge in NE'/ sec. 2. E. H. Bailey (oral 

 communication, 1962) reported the limestone to be 

 thin bedded and traceable for about 1,000 feet in a 

 westerly direction. It is sandwiched between green- 

 stone on the south and sandstone on the north. Ihe 

 limestone sequence is about 7 feet thick in a tributary 

 to House Creek, but it is a little thicker to the west. No 

 chemical analyses are available, but the limestone may 

 be impure (Honke and \'er Planck, 1950, p. "5). Be- 

 cause of its inaccessibility and small reserves, the 

 deposit is undeveloped and does not seem to be of 

 economic interest. 



Other reference: Logon, 1947, p. 333. 



Kolilman (Coleman) Culch deposit. Location: 

 Sec. 1 3, \. 8 N., R. 1 3 W., M.D., about 1 '/, miles north 



