96 



California Division of Mines and Geology 



Bull. i97 



for 2 miles up the south side of the canyon. According 

 to Dibblee (1950, p. 25), "it consists of about 50 feet 

 of gray-white, hard, sandy, algal limestone." It rests 

 unconformably on the Jalama Formation (Creta- 

 ceous) . At one time the material was quarried for road 

 material (Dibblee, 1950, p. 25, 80, plate 4). 



San Miguelito (Union Sugar) deposit. Location: 

 Possibly S'/j sec. 18 or N'/^ sec. 19 (proj.), T. 6 N., R. 

 34 W., S.B., 3/2 to 4 miles southwest of Lompoc; Lom- 

 poc 15-minute quadrangle. Ownership: C. S. Larsen, 

 Lompoc (1925). 



On the north side of San Miguelito Canyon, five 

 small limestone deposits were worked to depletion by 

 Union Sugar Company from about 1900 to 1919. Dur- 

 ing that interval, approximately 100,000 tons of lime- 

 stone were produced for use in sugar refining. The 

 material was hand cobbed and hauled 6 miles by wag- 

 on to Lompoc. Rail shipments were made from there 

 to Betteravia and, for a while, to Oxnard. 



Broken and distorted beds of "pure white fossilifer- 

 ous limestone", which graded into "siliceous lime- 

 stone conglomerate", occurred as five distinct deposits 

 over 40 acres of land (Huguenin, 1917, p. 740). The 

 deposits apparently are depleted but may have been 

 part of what was mapped as Quaternary landslide 

 (Dibblee, 1950, plate 3). According to Dibblee (1964, 

 oral communication), the landslide debris north of 

 San Miguelito Creek is largely composed of "lime- 

 stone" which is typical of the basal part of the Monte- 

 rey Formation. That the landslide material was 

 worked is indicated by the remnants of several small 

 pits there. However, the identification of the Union 

 Sugar deposits is tentative, as available analyses show 

 the carbonate rock of the Monterey Formation to be 

 generally dolomitic. 



Other references: Aubury, 1906, p. 81-82; Tucker, 1925, p. 553. 



Sierra Blanca deposit. Location: SE'/ T. 7 N., R. 

 27 W., SW'X T. 7 N., R. 26 W., and N'/ T. 6 N., R. 26 

 W., S.B., 15 to 17 miles north of Santa Barbara; San 

 Rafael Mountain and Gibraltar Dam 15-minute quad- 

 rangles. Ownership: Lies within Los Padres National 

 Forest (San Rafael Wilderness Area). 



The Sierra Blanca limestone deposit is situated a 

 few miles south of Big Pine Mountain which, at 6,828 

 feet elevation, is the highest point in the San Rafael 

 Mountains. The deposit is exposed as an elongate belt 

 traversing elevations ranging from 3,100 to 4,900 feet. 

 Except where its western end is crossed by Forest 

 Service road, the limestone belt is nearly inaccessible. 

 Because of its remote location, the deposit remains 

 undeveloped although mapping and limited sampling 

 indicate large reserves of good quality limestone. 

 Around the turn of the century, the east end of the 

 deposit was examined near the Moraga Ranch as a 

 source of lithographic stone by the Loma Blanca Lith- 

 ographic Stone Company (Aubury, 1906, p. 80). 

 However, it was considered unsuitable for litho- 

 graphic use. 



The limestone deposit is exposed as a continuous 

 belt that extends 5'/2 miles southeastward from the 

 East Fork of Santa Cruz Creek (1 mile west of Big 

 Pine Mountain Road) to a point 1 mile west of Mono 

 Creek (see figure 9). It consists of a distinctive se- 

 quence of middle Eocene bioclastic limestone which 

 was named the Sierra Blanca Limestone by Nelson 

 (1925, p. 352-354). The Sierra Blanca Limestone also 

 is exposed 1 to 2 miles to the north along the Big Pine 

 Mountain road, but these deposits appear to be too 

 small to be of economic value. Locally, the carbonate 

 unit rests unconformably on Upper Cretaceous sedi- 

 mentary rocks and is overlain conformably by Eocene 

 shale and sandstone. The limestone unit dips moder- 

 ately to steeply northeast, although there may be local 

 variations due to folding and faulting. 



Much of the limestone is pale buff, or, less often, 

 grayish buff to brownish gray, and weathers to a very 

 light gray. Typically, it is dense, hard, poorly bedded, 

 and breaks with an uneven fracture. It is composed of 

 fine to coarse organic debris derived from algae, 

 Foraminifera, and various megascopic shell forms. Oc- 

 casional impure, sandy horizons are reported, particu- 

 larly in the upper part of the unit (Keenan, 1932, p. 

 65). The bulk of the unit is relatively pure, as indicat- 

 ed by the chemical analyses in table 2 1 . The limestone 

 is of adequate quality for cement manufacture and if 

 analyses are representative, some of the limestone ap- 

 pears to be sufficiently pure for use in lime and chemi- 

 cal manufacture. 



Table 21. Chemical analyses of limestone from the Sierra 

 Blanco deposit, Santa Barbara County. 



AI.O,+ 

 Sample OO MgO Fe^Oj S1O2 P2O5 



M. F. KEENAN ' 



9)0 K,- 50.73% 3.00% 1.80% 1,60% trace 



930 P 54.32 0.71 0.94 0.96 trace 



930 Q_ 55.33 0.32 0.56 0.24 trace 



930 R .54.88 0.66 0,66 0,42 none 



G. W. WALKER ' 



0.37 + 

 5 53.07 1,14 0,33 2.01 ND 



CALIFORNIA DIVISION OF MINES AND GEOLOGY ' 



SB 1 54.31 0.58 0.48 1.04 (1,06% 



SB 2 54,47 0.66 0.46 0.76 0,08 



SB 3 54,31 0.53 0.56 0,94 0.06 



SB 4 54.60 0.62 0.52 0.48 0.05 



SB 5 54.77 0.54 0.32 0,56 0.08 



SB 6 .54.70 0.59 0.34 0,44 0,08 



SB 7 54.90 0.52 0.32 0,28 0,06 



SB 8 54.70 0.46 0.44 0,62 0,05 



' Samples collected by M, F, Keenan. September 19.10. from bank o( Indian 

 Oeek and represent the middle 55 feet of the stratigraphic thickness of 

 the 225-foot-thick limestone unit, Analy/.ed by Leslie Larneu. Los Ange- 

 les (Keenan, 1^2, p, 7(1) 



^ Composite grab sample from Big Pine Mountain road cuts representing 70 

 to 80 feet of stratigraphic thickness. Analyzed by P T, Bee, Abbot A. 

 Manks, Inc., San Francisco {Walker. I*J50a, p, 5), 



^ Grab samples collected at about 4()-foot intervals from west to cast along Big 

 Pine Mountain road by Oliver E. Bowen, California Division of Mines 

 and Geology, Analyzed by Abbot A. Hanks, Inc, San Francisco, 1953. 



ND = Not done 



