46 



California Division of Mines and Geology 



Bull. 197 



Deposit A. A sinuous line of outcrops is exposed 

 more or less continuously along an unnamed creek for 

 6,000 feet between NW'/,NW/, sec. 14 and NW cor. 

 sec. 1 1 . Although 5 to 10 feet of soil overburden masks 

 the limestone on both sides of the creek, the westerly 

 strike of the bedding in places indicates the deposit 

 locally might extend farther east and west than is 

 shown on the map. The character of the limestone is 

 quite variable in texture and color, and some is sili- 

 ceous. At the south end, two small quarries are devel- 

 oped in limestone that is predominantly blue gray and 

 medium crystalline. A few hundred feet to the north, 

 near the old stone kiln remnants, fine- and coarse- 

 crystalline, off-white to light-gray types of limestone 

 are found. Obscure planar structures suggest a N 75° 

 W strike with a vertical to steep south dip. Farther 

 north in SW/^SW^ sec. 11, bold outcrops of fine- to 

 extremely coarse-crystalline, white- to blue-gray, 

 high-calcium to highly siliceous limestone exist. At a 

 tiny quarry near the south end of the outcrops, a 2- 

 foot-thick interbed of schist indicates that at least part 

 of the deposit is flat-lying. The area was explored by 

 diamond drilling in 1955 by Marquette Cement Com- 

 pany. 



The most extensively developed part of Deposit A 

 lies near W'/ cor. sec. 1 1. Here, the predominant types 

 of limestone are; 1) off white, coarse crystalline with 

 occasional gray bands, and 2) gray, fine to medium 

 crystalline. Results of chemical analyses of each of 

 these rock types are given in table 9. Sample CH-2 

 indicates the white limestone to be of high quality, but 

 sample CH-1 shows about 3 percent each silica and 

 magnesia to be present in the gray rock. The main 

 quarry is nearly 1,000 feet long, 50 to .^00 feet wide, 

 and has a maximum face of 60 or 70 feet. An estimated 

 300,000 tons of limestone has been quarried here; two- 

 thirds of this reportedly was used for riprap along the 

 San Lorenzo River about 1956-57. Other small quar- 

 ries may have been developed elsewhere in the deposit 

 but were not recognized. 



Deposit B. Located mainly in SE'/ sec. 3, this 

 deposit has provided the main source of lime-rock for 

 Cowell since about 1910. The deposit is about 900 feet 

 long, at least 300 feet in maximum width, and is ex- 

 posed through a total relief of about 100 feet. A little 

 schist is exposed on the south wall, and thin streaks of 

 biotite-garnet schist have been penetrated by drill 

 holes. The deposit appears to dip gently to steeply 

 south and may be broken to some extent by faults. As 

 much as 10 feet of soil overburden plus vegetation and 

 quarry debris tend to conceal the areal extent of the 

 deposit. Diamond drilling conducted by Marquette 

 Cement (>)mpany in 1955 reportedly penetrated lime- 

 stone, with only thin streaks of foreign matter, to a 

 depth of 200 feet. Most of the limestone is off white to 

 light gray with some dark gray banding, coarse crys- 

 talline, and locally graphitic. The high calcium con- 

 tent of the limestone is reflected in the analyses of 5 

 samples — CH-3 and 4; SACR-1 to 3 — given in table 9. 



It is interesting to note the consistent differences in 

 contents of MgO, SiOj, AljO,, and PjO, reported for 

 the two groups (SACR, CH) of samples. The differ- 

 ences probably reflect the analytical methods em- 

 ployed by the analysts more than the chemistry of the 

 samples. 



Deposit B is developed by an irregularly benched 

 pit-quarry with maximum dimensions of about 800 

 feet by 300 feet by 100 feet. It is estimated that 500,000 

 to 1 million tons of limestone were produced from this 

 deposit prior to 1947. Most of this was hauled to kilns 

 at Rincon for calcining. Since 1947, only minor 

 amounts of rubble and architectural stone have been 

 taken. Additional quarrying apparently was con- 

 ducted immediately to the southeast, but quarry de- 

 bris masks any limestone that may have cropped out 

 in that area. 



Deposit C. This deposit consists of limestone ex- 

 posed intermittently over an elliptical area 1,700 feet 

 by 1,100 feet in NW'/ sec. 11. Much of the limestone 

 is coarse to very coarse crystalline, white to light gray, 

 and high calcium. It is interbedded with schist to some 

 extent and is overlain to the east by gently dipping 

 beds of Miocene sandstone. Crude bedding in some 

 places indicates that stratification dips 55 to 65° N; but 

 some variations in dip, as well as brecciation features, 

 suggest that the deposit is structurally complicated. 

 Although the relative proportions of limestone and 

 schist are not known, the deposit is exposed through 

 300 feet of relief and contains at least several million 

 tons of limestone. The deposit is developed by an old 

 hillside quarry approximately 120 feet by 60 feet with 

 a maximum face of 50 feet. It is accessible by a dirt 

 road from the north. 



Deposit D. Located in the SW'X sec. 2, this deposit 

 appears to have a westerly elongation of more than 500 

 feet and a maximum width along the road of 300 feet. 

 It consists of coarse-crystalline, off-white to gray, 

 banded limestone with some very coarse-crystalline 

 white limestone. Biotite schist borders the deposit on 

 the north; the other boundaries are masked by soil and 

 heavy vegetation. Near the quarry, the apparent strat- 

 ification dips steeply south. The deposit was worked 

 many years ago by means of an open quarry about 100 

 feet in diameter with a maximum face of 30 feet. 



Deposit E. Situated in SW'/i sec. 2, a few hundred 

 feet north of deposit D. It was tentatively mapped by 

 G. W. Leo (1967 and unpublished Stanford thesis) as 

 an elliptical mass 1,400 feet long by 700 feet wide. 

 Limestone outcrops and float a few hundred feet to 

 the east may be an extension of the deposit. Much of 

 the limestone at the quarry is fine to medium crystal- 

 line and light to medium gray; however, some is coarse 

 crystalline and white to gray. Ihe attitude of the 

 deposit is not known, and the mass appears to be bro- 

 ken by faulting. Details of the deposit are concealed by 



