16 



California Division of Mines and Geology 



Bull. 197 



: :.26 



) 2.2! 



4 1.10 



5 1.98 



6 2,65 



7 10.81 



8 1.10 



1 1.90 



10 2.!i 



11 1,69 



0.44% 0,20% N,D 96,60% N,D 



0,5) O.2.! 

 0.76 mcl. 

 0, 

 0, 



ND 



9>48 N,D 



075% ND, 

 110 ND 



!!80% 96,00 0,J5% N,D. ND. 



mcl, 

 0,09 

 0J4 

 161 

 mcl 

 0,20 

 Oil 

 0,40 



J4J2 

 j)9i 

 i,U0 

 4)2,1 

 480 

 ND 

 Vl 89 

 i41i 



97.00 

 ND 

 ND 

 ND 



97 80 

 96 74 

 ND 

 ND 



1.25 

 0.J8 

 0.85 

 0.80 

 ND 

 0.1.1 

 018 

 029 



ND. 

 ND. 



ND, 

 ND 

 If 

 ND, 

 ND 

 ND 



ND. 



■O0!% 



007 



0,21 

 ND 

 N.D 



0.07 



0,14 



ND 

 ND 



42.70% 



42,68 



ND 



42,20 



ND 



41,20 



ND. 



ND. 



ND 



N.D. = Not determined. 



incl. = included with .ALO,, 



tr, = trace 



Samples 1-" are cryslalhne limestone similar to the Sur Series of .Monterey 



Count)- 

 Sample 1 from old quarry near "Trout Farm" (North of Lockhart Ranch). 

 Samples 2-3 and 5-7 from Lockhart Ranch 

 Sample 4 from near Inverness Park. 



Samples 8-11 are Franciscan Formation limestone from Olema deposit. 

 Analyses 1-4 and 8-9 published in Eckel (1933, tables 1 and 2), 

 .Analyses 5-6 and 10-11 made by Abbot A Hanks. Inc , 1955, 

 .Analysis 7 made b\ Lydia Lofgren, Calif Division of .Mines and Geology, 



19A2- 



Napa Junction deposits. Location: E'/j sec. 24, T. 

 4 N., R. 4 W., an(J W'/, sec. 19, T. 4 N., R. 3 W., M.D., 

 1 mile south of Napa Junction and ^ miles north of 

 \allejo; Cordelia 7'/,-minute quadrangle. Ownership: 

 Principally Basalt Rock Company, 8th and River 

 Streets, Napa (1962). 



Impure limestone and associated clay were used to 

 make cement from 190.3 to 1918 by Standard Portland 

 Cement Company. The company reportedly ceased 

 operation of their Napa Junction plant in September 

 1918, apparently because most of the better quality 

 limestone was used up. The Napa Junction deposits 

 are not known to have been worked since 1918. 



T he limestone is exposed as low outcrops in two 

 areas separated by alluvium. The north, or main, 

 deposit occupies a low, west-plunging ridge on which 

 are located a series of elongate pits. Because of thick 

 soil, exposures are limited mainly to the steep faces of 

 the pits. Here, the deposit consists of .50 to 100 feet of 

 crudely bedded, bioclastic limestone and related im- 

 pure carbonate rocks that strike about N 75° E and dip 

 35° N. Underlying the clastic beds at the base of the 

 exposed south face of the largest pit are beds of shale 

 with small lenses and concretions of fine-grained, 

 blue-black, impure limestone. It seems apparent that 

 the upper beds served as the principal source of lime- 

 stone and clay. These range in composition from near- 

 ly pure bioclastic limestone, with only scattered 

 noncarbonate fragments, to a fossiliferous mudstone 

 containing large amounts of mudstone (luffaceous?) 

 pebbles and fossil debris, (x)lor of the rocks varies 

 from greenish gray to yellowish brown and grain size 

 ranges from fine sand to gravel. Most of the carbonate 

 material appears to be shell and algal debris — proba- 

 bly derived from a near-shore reef. The age of the 



limestone could not be determined although Weaver 

 (1949, plate 15) shows it to be part of the Eocene 

 Domengine Formation. In contrast, however. Weaver 

 indicates similar limestone half a mile to the south to 

 be part of an undivided sequence of Late Jurassic or 

 Early Cretaceous age. 



At the south deposit the carbonate rocks are similar 

 to those of the main area, but they may be less pure 

 and finer grained. Certainly the south exposures are 

 less extensive, covering a low rise perhaps 300 to 400 

 feet in diameter. The rocks are not well bedded here 

 although one bed showed a dip of 70° W. A third and 

 even smaller outcrop is exposed in a small pit 1,000 

 feet northwest of the main outcrop. 



Because the limestone of the three areas show com- 

 mon characteristics, they are no doubt of common 

 origin and probably of the same formation. However, 

 the deposits probably are not contiguous, as there is 

 evidence of faulting and brecciation in the main and 

 south areas. 



Chemical analyses of the limestone were made 

 many years ago and are shown in table 3. According 

 to Eckel (1913, p. 121-122), the deposit contained two 

 grades of limestone that ran 60 to 65% and 85 to 90% 

 calcium carbonate. It is obvious that very little "high- 

 grade" limestone remains in the deposit although low- 

 grade limestone and related calcareous beds may be 

 extensive, particularly in the main area. Reserves are 

 not known; but, even if large, the deposit appears to 

 be too impure for cement manufacture and other uses. 

 Most of the reserves are expected to be north of and 

 down dip from the main quarry area. 



Table 3. Chemical analyses of limestone from Napa Junction 

 deposits, Napa County (from Eckel, 1913, p. 122). 



Sample SiO, AW, Fe.O, CaCO, MgCoT 



High-lime rock 



No. 1 6,6!% !,61% 1,26% 8.5.17% 1.8!% 



No. 2 7.12 2.!6 1,16 87,70 0,84 



Low-lime rock 



No. 1 20.87 10.50 !.50 62,76 1,48 



No. 2 20.2! 8.68 !.ll 65.2! 1.72 



Development of the limestone was mainly near the 

 E'X cor. sec. 24 along the north side of the ridge where 

 three linear pits extend continuously over an area 1,- 

 700 feet by 200 to 400 feet. Excavation apparently ex- 

 tended deeper than the present pit, which is as deep 

 as 40 feet and has been partly filled with debris and 

 slope wash. Smaller pits lie west and north of the main 

 quarries. In the south area, the pit is about 200 by 300 

 feet in area and is more than 25 feet deep. Most of the 

 pits were worked below the water table and contain 

 ponded water. Based on the observable sizes of the pits 

 (April 1962), it is estimated that at least 1.5 million 

 tons of limestone and associated clay was produced 

 during the 15 years of operation. The raw materials 

 were hauled in small dump cars by rail to the cement 

 mill located immediately north of the main quarry. 



