1978 



Limestone in the Coast Ranges 



21 



as a smelting flux at the ASAR(X) smelter at Selby. 

 The Cow ell interests acquired the Spreckels holdings 

 in 1915 (Logan, 1947, p. 221). 



The ()nl\- other known production was by Mount 

 Diablo Lime Marl Company from 1924 to 1927 when 

 calcareous tufa and travertine were quarried from the 

 small northwest deposits in sec. 7 (proj.). Ihe princi- 

 pal production probably came from the quarry just 

 north of Treat Lane. The material was crushed and 

 ground for sale mainly as a soil amendment. Some 

 travertine also w as sold to the Mountain Copper Com- 

 pany at Martmez as a flu.x for smelting (Laizure, 1924, 

 p. 85). L. C. Hopper acquired a lease on the property 

 in September 1926 and may have produced a little 

 limestone (Laizure, 1927, p. 16). Although the north- 

 west deposits have not been utilized as commercial 

 sources of limestone for many years, the carbonate 

 rocks and underlying sandstone half a mile northwest 

 of Treat Lane (X'/, sec. 7) have been excavated in 

 recent years, apparently for fill purposes. 



Carbonate rocks are found in two distinct areas on 

 Lime Ridge and are referred to herein as the main and 

 northwest deposits. By far the most extensive are the 

 main deposits, which cover an irregular area centering 

 in sec. 17 (proj.) and extending into SE'/ sec. 8 and 

 N'/, sec. 20. .Altogether, these deposits cover close to 

 half a square mile on both sides of Lime Ridge but 

 mainly on the southwest side. The northwest deposits 

 are much smaller, covering 10 acres or less along the 

 crest of Lime Ridge. They consist of three small 

 deposits, the largest lying just north of Treat Lane and 

 half a mile southeast of the other two. 



Even though limestone reserves are largely deplet- 

 ed, quarry exposures indicate that the deposits were 

 thicker than 15 to 20 feet in only a few places. The 

 deposits consist of travertine and calcareous tufa de- 

 posited surficially in and on sandstone of Eocene age 

 (Domengine Formation to the southeast; Markley 

 Formation to the northwest). Carbonate-rich spring 

 waters emanating during Quaternary time from a 

 northwest-trending fault and associated fractures are 

 believed to have caused formation of the deposits. 

 Deposition of carbonate materials has apparently 

 ceased, except possibly in SE'/, sec. 8 where there is 

 some spring activity. 



Travertine appears to be the highest quality carbon- 

 ate rock present, but its relative abundance is uncer- 

 tain. It is gray to tan, dense, hard, fine grained, and 

 generally faintly banded and swirled. It is commonly 

 brecciatcd and recementcd with coarse crystalline cal- 

 cite. The travertine probably ranges from calcitic frac- 

 ture fillings in sandstone on one hand to calcareous 

 tufa on the other. The calcareous tufa generally over- 

 lies the travertine and represents a later or more surfi- 

 cial stage of deposition. The tufa is off white to tan, 

 soft, porous, and crudely stratified. It is somewhat 

 impure and may actually grade into caliche, from 

 which it is difficult to distinguish. Chemical analyses 

 of the various types of carbonate rock are given in 



table 4. Aside from artificial cuts, the carbonate 

 materials are poorly exposed and commonly veneered 

 with soil. The hummocky topography and brecciation 

 features indicate that the deposits arc broken and com- 

 plicated hv faults and landslides. The geologic features 

 of the Lime Ridge deposits are depicted by Ivan Col- 

 burn in his doctoral thesis in geology (1961, Stanford 

 L'niversity). 



Table 4. Chemical analyses In percent by weight of corbonote 

 rock from Lime Ridge (main deposits). Contra Costa County. 



N D = Noi done 



Samples collected 1 1-7-62 by Earl W. Hart and analyzed February and March 



196} by Lydia Lofgren, Division of Mines and Geology. 

 Sample 1 — typical calcareous tufa; soft, porous, ligtit tan; from main quarry 



near Treat Lane, F-'/, 7 — IN — IVV (pro) ) 

 Sample 2 — typical travertine; buff to Ian, hard, dense, fine grained uilh some 



crystalline vein calcite, from quarry m NV\'',,, SE'/, 17 — IN — IVV (proj.). 

 Sample .t — impure calcareous tufa or caliche; lighi tan, soft, porous, with 



some sand and rock fragments; from quarry in SW'/, 1~ — IN — IVV 



(proj.). 



Development of the Lime Ridge deposits is quite 

 extensive, and virtually all deposits were worked to 

 some degree. The principal workings center in S'/; sec. 

 17 where a series of quarries, benches, and pits are 

 developed in an irregular and often merging pattern. 

 Most cuts are shallow but some are as high as 40 to 50 

 feet and one large benched quarry has a relief of 200 

 feet. Less extensive workings are found at the main 

 deposits in N'/ sec. 20, N'/z sec. 17, and SE'/, sec. 8. 

 Although the amount of material quarried cannot be 

 determined from the irregular workings, as much as 

 10 million tons of carbonate rock may have been pro- 

 duced from the main deposits if the cement mill oper- 

 ated even close to capacity. In the northeast area, each 

 of the three deposits is developed by quarries. The 

 deposit near Treat Lane was worked by two quarries, 

 the largest being about 125 feet in diameter and 20 to 

 .HI feet deep. Production here is estimated to have 

 totaled 15,000 to 20,000 tons. Haifa mile to the north- 

 west, two deposits 600 feet apart are developed by 

 quarries v^hich may have yielded 10,000 tons of car- 

 bonate rock. 



Reserves of travertine and related carbonate rock 

 are impossible to estimate but are almost totally con- 

 fined to the main deposits. At the main deposits, the 

 reserves reportedly were approaching depletion (Da- 

 vis and X'ernon, 1951, p. 567). Calcareous tufa and 



