1978 



Limestone in the Coast Ranges 



43 



rocks of probable Cretaceous age commonly intrude 

 the metamorphic rocks. The principal limestone 

 deposits are found northwest of Santa Cruz, west of 

 Felton, and northeast of Davenport. Substantial lime- 

 stone reserves appear to exist in each of these areas. 

 Silica is the principal impurity at most deposits al- 

 though magnesia causes problems locally. Schist in- 

 terbeds and granitic dikes are common enough to 

 cause a significant waste factor at most deposits. 

 Nonetheless, most of the deposits appear to be suffi- 

 ciently large and pure to warrant further exploration 

 as potential sources of limestone. 



In 1964, the only active limestone deposits were the 

 San X'icente (Pacific Cement and Aggregates, Inc.), 

 Pacific Limestone Products Company, and Holmes 

 deposits. These and other known deposits are de- 

 scribed alphabeticallv below. 



Bonnie Doon deposit. Location: SW'/^ sec. 2.\ 

 SE'/, sec. 26. and NVV'/, sec. i6, T. 10 S., R. } W., M.D., 

 3 miles east-northeast of Davenport; Ben Lomond l.'i- 

 minute quadrangle. Ownership: Mainly Pacific Ce- 

 ment and .Aggregates Division, Lone Star Cement 

 Corporation, 400 Alabama Street, San Francisco 

 (1963). 



The deposit has been quarried to a minor extent in 

 NE'/SE'X sec. 26 by Hinds and Packard, who calcined 

 lime between 1890 and 1900. Remnants of their stone 

 kiln and small quarry site can still be seen just east of 

 Bonnie Doon road. This property was later acquired 

 by Cowell Lime and Cement Company, which never 

 worked the deposit. The S.H. Cowell Foundation now 

 holds the property. The main limestone outcrops to 

 the southeast, in sees. 25 and 36, are on land belonging 

 to Pacific Cement and Aggregates. Other than exten- 

 sive diamond drilling in SW'/i sec. 25 done by the 

 present owner during 1959 and 1960, this portion of 

 the deposit is undeveloped.' Also, two prospect tun- 

 nels are shown on the Davenport 7'/,-minute quadran- 

 gle (1959 ed.) in SVV ){ sec. 25. 



The Bonnie Doon deposit consists of one or more 

 bodies of crystalline limestone and is intermittently 

 exposed over a northwest-trending area 3,500 feet long 

 and as much as 1,500 feet wide. Miocene sedimentary 

 rocks overlap the deposit on most sides, concealing the 

 true extent of the deposit. The approximate distribu- 



' Development of thrs deposit was cortipleted in mid-1970 to supply limestone 

 — formerly supplied by the San \'icenie Creek deposit — to the PCA ce- 

 ment plant at Davenport The company reports (Herb Gaskin, W7I. 

 personal communication) that the new quarry is IcKated in S\Vy,SWV, 

 see- 25. T 10 S,. R. J W , nearly i miles east-norlhcasi of the plant 'I'he 

 floor of the quarry is at an elevation of 800 feet. The multi-benched face 

 is worked downward in a manner similar to that at the San \"icentc Creek 

 quarry \ maximum overburden of 100 feet is anticipated as the quarry 

 is developed northeastward .\fter quarrying, the crystalline limestone is 

 crushed in a semiportable plant ( 1.140-tons-per-hour capacity) and stored 

 in a large concrete silo prior to a -1-mile lielt-conveyor trip to the cement 

 plant. Shale from a new quarry in the Monterey Formation (-) provides 

 much of the alumina and silica needed to make cement. This quarry is 

 situated along the conveyor route, halfway between the cement plant and 

 limestone quarry, in sec. H The new crushing-storagc-transfer facilities 

 cost $7 million to install Capacity of the conveyor is I.OOO tons of lime- 

 stone or 630 tons of shale per hour. 



tion of limestone is shown by Branner et al. (1909, 

 maps) and (^lark (1970). The limestone is white to 

 gray and generally coarse crystalline, but some is fine 

 crystalline and may be dolomitic or siliceous. Analy- 

 ses of two sainples from the Bonnie Doon quarrv show 

 94% and 95.87% CaCOj and 2.8% and 2.93% MgCOj 

 respectively (Eckel, 1933, p. 353). Some schist in- 

 terbeds and granitic dikes occur locally with the lime- 

 stone. Limestone reserves are difficult to assess 

 because soil and vegetative cover mask the continuity 

 between outcrops. The deposit is uell disposed for 

 open-quarry development, the outcrops occurring 

 over 600 feet of relief. Proximity of Bonnie Doon and 

 Smith Grade roads render good accessibility. 



Pacific Cement and Aggregates recently drilled 

 about 30 exploratory holes in SWy; sec. 25, mainly 

 above an elevation of 1,000 feet. Although some minor 

 schist beds were encountered, approximately 7'/, mil- 

 lion tons of limestone reserves reportedly were devel- 

 oped. The company contemplates utilizing this 

 deposit as a future source of limestone for its Daven- 

 port cement plant, which is 6 to 7 miles away by road. 



Cowell Home Ranch deposits. Location: Sees. 2, 

 3, 9, 10, 11, 14 (proj.), T. 11 S., R. 2 VV., M.D., I'/j to 

 3 miles west and northwest of Santa Cruz City Hall; 

 Santa Cruz and Felton 7'/2-minute quadrangles. Own- 

 ership: University of California at Santa Cruz and 

 S.H. (Lowell Foundation, 25 California Street, San 

 Francisco (1963). 



The Cowell Home Ranch deposits were first devel- 

 oped by I. E. Davis and A. P. Jordan who established 

 a lime plant and quarry in 1851 (Logan, 1947, p. 318- 

 319). The kiln was located near N'W cor. sec. 14, just 

 west of the present ranch house. Limestone immedi- 

 ately to the south and within half a mile to the north 

 of the kiln area was the early source of lime rock. 

 Later, Davis joined with Henry Cowell and continued 

 operating the deposits through the 188()s. During this 

 period, additional quarries and kilns were established 

 1 Vj miles to the west in sec. 9 at the Wilder Creek-Cave 

 Gulch deposit. About 1895 Cowell acquired sole own- 

 ership of the limestone property and formed the 

 Henry Cowell Lime and Cement Companv. Bv the 

 early 1900s, Cowell controlled nearly all of the lime- 

 stone reserves in the vicinity of Santa Ouz and some 

 of the deposits near Felton and Bonnie Doon (see IXL 

 and Bonnie Doon deposits). The early quarries on the 

 Home Ranch eventually were closed down, and most 

 of the limestone produced affer about 1910 came from 

 the quarry in SE'/, sec. 3. Continuous kilns were erect- 

 ed at Rincon Station to burn this limestone; but only 

 the dense finer crystalline limestone could be effec- 

 tively processed, the coarse crvstalline \Ahite lime- 

 stone being burned in pot kilns near the ranch house 

 (Hugucnin and Costello, 1920, p. 237). About 1920, 

 pot kilns were erected at Rincon Station and, thereaf- 

 ter, all the limestone was burned at the new facilities. 

 Other quarries in sees. 2 and 11 were operated less 



4 — B9454 



