38 



California Division of Mines and Geology 



Bull. 197 



The deposit consists of three small limestone masses 

 that extend southwestward for 1,500 feet. The largest 

 of these is shown by Bailey and Everhart (1M64, plate 

 1) to be faulted and to cover an irregular, northeast- 

 trending area 600 feet by 275 feet in maximum dimen- 

 sions. It consists of typical Franciscan limestone and 

 moderate amounts of thin chert interbeds. At the 

 quarry, the strata dip 20°-35° S and have an estimated 

 exposed thickness of 30 feet. Here the limestone varies 

 from fine grained, light gray, dense, and foraminiferal 

 to dark gray, fine crystalline, and bituminous. Sand- 

 stone and volcanic rocks of the Franciscan Formation 

 are in contact with the deposit on the north. 



When examined in July 1962, the main limestone 

 mass was developed by an irregular quarry 250 feet by 

 100 feet. It had been worked by two benches through 

 a relief of about 80 feet. Roughly 10,000 to 20,000 tons 

 of rock had been removed. \'egetation indicates the 

 quarry has not been worked for at least 20 years. Two 

 other quarries are indicated 800 feet and 1,200 feet to 

 the southwest in a small lens (Bailey and Everhart, 

 1964, plate 1). These quarries were not examined but 

 are probably small. 



Because the limestone bodies are small and com- 

 monly contain chert interbeds, future use of the lime- 

 stone appears to be limited to crushed rock. 



Other references: Crawford, 1894, p. 394; Aubury, 1906, p. 82-83; Davis 

 and Jennings, 1954, p. 364. 



Lyndon deposits. Location: S'/, sec. 28, T. 8 S., R. 

 1 W., M. D., I mile south of Los Gatos; Los Gatos 

 15-minute quadrangle. Ownership: Guadalupe Col- 

 lege!?), Los Gatos (1962). 



The Lyndon deposits lie on St. Josephs Hill, mainly 

 in NWX SE'/i sec. 28. As mapped by Bailey and Ever- 

 hart (1964, plate 1), the deposits consist of a number 

 of small lenses of Franciscan limestone extending over 

 an area half a mile long by 1,000 feet wide. The largest 

 lens is about 700 feet long and a little more than 100 

 feet wide at its maximum. It consists of light-gray, 

 fine-grained, foraminiferal, somewhat siliceous lime- 

 stone with lesser amounts of fine crystalline, dark- 

 gray, bituminous limestone. Chert interbeds are com- 

 mon throughout the limestone and may comprise a 

 quarter of the deposit. The strata show variations in 

 attitude and probably are faulted. The deposit was 

 developed by a narrow hillside quarrv about 200 feet 

 long with a 20-foot face (visited July 1962). Produc- 

 tion, which amounted to only a few thousand tons, 

 was made many years ago judging from the considera- 

 ble plant growth. A small quarry, 700 feet to the south- 

 east, exposes another small lens. It is not known who 

 worked these deposits, but it may have been the Los 

 Gatos Lime Company (which see). 



Below the Franciscan limestone outcrops, Eckel 

 (1933, p. 356, 359) noted a large deposit of travertine 

 as much as 30 feet thick. Apparently it is undeveloped. 



Other reference: Davis and Jennings, 1954, p, 364, 408. 



Mindego deposits. Location: Mainly sees. 7, 18, 19, 

 T. 7 S., R. 3 W., and sec. 15, T. 8 S., R. 3 W., M. D., 

 1'/, to 3 miles east, 1 mile west and 8 miles southeast 

 of La Honda; Half Moon Bay and Ben Lomond 15- 

 minute quandrangles. Ownership: Not determined. 



Thin beds and lenses of limestone are reported in 

 the Mindego Formation (Oligo-Miocene) at several 

 localities near La Honda and southeast of that settle- 

 ment. These deposits are described by Cummings et 

 al. (1962, p. 192) as follows; 



"Some of tfiese are calcorenites overlying volcanic sfrafo. Many 

 are bioclostic in origin and consist largely of fragments of smalt 

 pelecypods and bryozoo. For exomple, along Waterman Creek in 

 sec. 15, T. 8 S., R. 3 W., one of tfiese limestone lenses is more tfian 

 1,000 feet long and nearly 100 feet tfiick ond is composed cfiiefly 

 of broken and compacted oyster sfiells. Other limestones occur 

 near tfie summits of Mindego and Longley Hills and in San Gre- 

 gorio Creek in the vicinity of Redwood Terrace." 



These same deposits were described as "limestone in- 

 clusions" and "clastic dikes" of Eocene age by Bran- 

 ner et al. (1909, p. 3, 8-9, map). 



None of these occurrences is known to be of eco- 

 nomic value, although the Waterman Creek deposit 

 appears large enough to warrant further investiga- 

 tion. The chemistry of the limestone is not known, 

 except that tuffaceous debris is reported to be com- 

 mon. 



Monte Bello Ridge deposits (including Bond, Win- 

 ship, Black Mountain). Location: E'/j T. 7 S., R. 3 

 W., and SW'X T. 7 S., R. 2 W., M. D., 5 to 8 miles south 

 and southwest of Los Altos; Palo Alto 1 5-minute quad- 

 rangle. Ownership: Multiple — includes Kaiser Ce- 

 ment and Gypsum Corp., National Realty Co., Mary 

 I. Crocker, Winship Estate, G. F. and A. Morrell, Em- 

 met Burns, and many others (1962). 



The Monte Bello Ridge deposits form a group of 

 numerous, small to medium-sized limestone bodies 

 that extends southeastward for 7/2 miles from a point 

 west of Page Mill Road in NW'/, sec. 10., T. 7 S., R. 3 

 W., to Stevens Creek near S'/ cor. sec. 33, T. 7 S., R. 

 2 W. The deposits lie on the northeast side and within 

 I'/, miles of the San Andreas fault, which obliquely 

 truncates the northwest end of the group. Part or all 

 of the deposits have been mapped by several geolo- 

 gists, but the only published maps are by Walker 

 (1950b, plate 1) and Dibblee (1966b). Part of Dib- 

 blee's map is reproduced in figure 3. Included in the 

 Monte Bello Ridge group of deposits are the proper- 

 ties of Bond (Franke, 1930, p. 9) and Winship 

 (Huguenin and Costello, 1920, p. 185), as well as most 

 of the deposits on Black Mountain (Permanente 

 deposit excepted). There has been no commercial de- 

 velopment of the limestone although considerable 

 trenching and core-drilling was conducted within 1/2 

 miles of Black Mountain by Permanente Cement 

 C^ompany (now Kaiser Cement and Gypsum Corpo- 

 ration), mainly about 1945. 



