36 



California Division of Mines and Geology 



Bull. 197 



Lydia Lofgren of the California Division of Mines and 

 Geology in 1962, showed 53.07% CaO, HS% MgO, 

 2.32% SiO;, .40% A1;0„ .40% Fe,0„ .01% P^O,, and 

 42. .15% ignition loss. 



The soft matrix material is off white to vellowish- 

 and reddish-brown, porous, impure calcium carbon- 

 ate. This no doubt is the "marl" quarried and pulver- 

 ized for agricultural use. 



The deposit is exposed over a small area as low, 

 scattered outcrops of hard limestone separated widely 

 by soil. When examined in July 1962, development 

 consisted of a shallow, irregularly benched quarry 200 

 to 300 feet in diameter. There has been no recent activ- 

 ity and future possibilities appear to be limited. 



Bailey and Everhart (1964, plate I) mapped the 

 deposit as an east- west lens, 500 feet long by 125 feet 

 in maximum width. They show three other lenses in 

 SE'/ sec. 19. The largest of these, lying 600 feet 

 northeast of the Bernal deposit, measures 1,100 feet by 

 200 feet. It was developed by a trench 100 feet long by 

 1 5 feet wide, which exposes 8 feet of limestone breccia 

 and caliche similar to that at the nearby quarry. The 

 map shows several other deposits of Eocene limestone 

 to the west. The largest of these, in sec. 20, T. 8 S., R. 

 2 E., is nearly half a mile long. It is exposed only as 

 scattered limestone fragments in heavy soil and is not 

 believed to represent a deposit of significant size or 

 purity. The Eocene deposits examined in the Santa 

 Teresa Hills have insufficient exposures to indicate 

 much commercial potential. Indeed, two of the depos- 

 its are brecciated and impure where they were quar- 

 ried. 



Other references: Franke, 1930, p. 9; Logan, 1947, p. 311-312; Davis ond 

 Jennings, 1954, p. 364. 



Calero deposit. Location: Near center sec. 8 

 (pro).), T. 9 S., R. 2 E., M. D., 4 miles southwest of 

 Coyote; Los Gatos 15-minute quadrangle. Ownership: 

 E. M. Fellows (estate), 23201 McKean Road, Morgan 

 Hill (1965). 



This deposit lies a little more than a mile south of 

 Calero Reservoir in a small valley a mile west of 

 McKean Road. It is exposed as an arcuate, northwest- 

 trending body of Franciscan limestone 1,800 feet long 

 by an average of 200 feet wide (Bailey and Everhart, 

 1964, plate I). The Calero deposit consists mainly of 

 fine-grained to medium-crystalline, light- to dark- 

 gray, thinly bedded, bituminous, locally brecciated 

 limestone, commonly with interbeds of black chert. 

 At the northwest end of the body, light-dove-gray, 

 pink, and brownish-red varieties of limestone were 

 observed (July 1962). Most beds exposed in the creek 

 dip moderately northeast and southwest, although 

 other dip directions are indicated at the extremities of 

 the body. Abrupt changes in attitude, plus brecciated 

 beds, suggest that the limestone body is broken by 

 faults. 



Judging from exposures near the quarry, the se- 

 quence of limestone beds is probably at least 50 feet 



thick. If an average thickness of 50 feet is assumed, 

 available reserves of limestone and chert would be in 

 the order of a million tons. Future potential of the 

 deposit is probably limited to crushed rock uses due to 

 the dispersion of chert interbeds throughout the lime- 

 stone. 



A single quarry situated in the middle of the deposit 

 on the north bank of the creek was worked prior to 

 1937, when E. M. Fellows acquired the property. The 

 quarry is 75 by 20 feet in plan with a 30-foot face. The 

 use of the quarried rock and other details of develop- 

 ment are unknown. In 1962 the owner reported that 

 the deposit was test drilled, but the results are un- 

 known. 



Castro Valley deposits. Location: Sec. 15 (proj), 

 T. 11 S., R. 3 E., and sec. 30, T. 11 S., R. 4 E., M.D., 

 3 to 4 miles southwest and south of Gilroy; San Juan 

 Bautista 15-minute quadrangle. Ownership; Mainly 

 Castro Valley Ranch (c/o H. S. Chase, Santa Bar- 

 bara), Sargent Ranch, and Shoemaker (Bloomfield) 

 Ranch (1963). 



Numerous lenses of limestone, associated with 

 other sedimentary and volcanic rocks of the Francis- 

 can Formation, are shown on the northeast flank of 

 the Santa Cruz Mountains by Allen (1946, plate 1). 

 The lenses lie in two principal groups centering in S'/j 

 sec. 15 (proj.) and 3 miles to the southeast in and near 

 SW/4 sec. 30. Some of these deposits were examined 

 briefly in July 1963. Scattered limestone bodies also lie 

 to the north and east (Allen, 1946, plate 1). 



The deposits in sec. 15 consist of a west-trending 

 series of detached lenses and masses. The largest is a 

 sinuous lens, roughly 1,500 feet long by 150 feet wide, 

 that dips north into the hill. On hill "1722", a faulted 

 mass 900 feet long by a maximum of 200 feet wide 

 appears to merely cap the ridge and may be relatively 

 thin. In sec. 30, the limestone bodies trend more to the 

 northwest and are smaller than shown by Allen. 1 he 

 limestone observed in each area is generally dark gray, 

 fine crystalline, bituminous, well bedded to platy, and 

 somewhat siliceous. Other types of limestone are light 

 gray or even dark gray mottled with white. All of the 

 limestone is abundantly associated with thin interbeds 

 of chert. \'ariable attitudes and common brecciation 

 features reflect the widespread faulting that has dis- 

 turbed and broken the many lenses. Some of the larger 

 faults are shown by Allen (1946, plate 1). 



Two or three tiny quarries, from which only a few 

 tens of tons of material were removed, were developed 

 in S'/2 sec. 30 many years ago for an undetermined 

 purpose. A chemical analysis by Matti Tavela of the 

 Division of Mines and Geology of typical mottled 

 (brecciated), bituminous limestone from a quarry in 

 SWy, sec. 30 showed 3.0% SiO^, 0.60% Al,0„ 0.19% 

 Fe^O,, 0.27% MgO, 51.8% CaO, 0.14% P,0, and 

 43.0% ignition loss. Reserves of limestone may aggre- 

 gate several million tons, but none of the individual 

 masses appears to contain more than a few hundred 



