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San Benito County

  • San Benito County Limestone, circa 1904 (From The Structural and Industrial Materials of California, Bulletin No. 38, California, State Mining Bureau, San Francisco, California, 1906.)

    "A belt of white crystalline limestone runs along the east slope of the Gabilan range, in places forming the main ridge. (See XIth Report, California State Mining Bureau, p. 370, Monograph XIII, U. S. Geological Survey, p. 181.)

  • San Benito County Mines and Mineral Resources, California (circa 1915-1916) – Excerpts from Report XV of the State Mineralogist, Mines and Mineral Resources of Portions of California, Chapters of State Mineralogist's Report Biennial Period 1915-1916, Part V. Monterey, San Benito, San Luis Obispo, Santa Barbara, Ventura counties, California State Mining Bureau, 1919, pp. 595-769.

    San Benito County, by Walter W. Bradley and C. A. Logan, Field Assistants. Field Work in September, 1914, and December, 1915.

    History and Geography (of San Benito County)

    "Crespi visited the region in 1772 and gave its chief stream the name of San Benedicto, in honor of Saint Benedict, but the name was later contracted to San Benito. The county dates its official existence from February 12, 1874.

    "With a population slightly over 8000 and an area of 1476 square miles, San Benito County is bounded on the north by Santa Clara and Santa Cruz counties, on the east by Merced and Fresno counties and on the south and west by Monterey. Most of the population resides in the few towns near the railroad in the northern part of the county.

    "The county consists topographically of a long, narrow valley flanked on each side by chains of the Coast Range, through which occasional passes give access to neighboring counties…."

    "Transportation facilities are limited. The Southern Pacific operates a branch line from Gilroy to Tres Pinos via Hollister, the county seat. Auto stages operate between Hollister and Sargent via San Juan Bautista and also give connection with the railroad at San Jose. Stage lines operate between Tres Pinos and San Benito daily, and via Panoche Pass to New Idria triweekly. The road crosses the river at many places where there are no bridges, and heavy rains therefore delay traffic, as the streams rise suddenly, and easily become unsafe to cross. The southern section of the county has no transportation facilities, but can be reached through Coalinga or Kern County; New Idria, east of the mountains, reaches the railroad easiest at Mendota.

    Geology, Areal and Structural (of San Benito County)

    "The county's geology has never been fully covered by any writer, but various geologists have visited sections of it and have recorded their observations. The writers' observations were necessarily confined to a hurried study of those mineral deposits which were working at the time of our visits or promised to become of especial interest because of present conditions…."

    "Structurally, the county shows two mountain piles of apparently diverse geologic formation, striking northwest and separated by a narrow valley filled with younger formations and detritus. Traversing the valley is the San Andreas Fault Zone, along which fresh movement occurred at the time of the San Francisco earthquake in 1906. On the southwest of this zone, forming the basement of the Gabilan Range and outcropping at places through the whole length of the county, granite and associated schists occur. Associated with these, are several square miles surrounding and including Gabilan Peak, are notable beds of metamorphosed limestones with which, as described particularly farther on, are deposits of barite and dolomite.

    "Volcanic activity is not indicated in this section, but as we go south toward The Pinnacles conditions change…."

    Mineral Resources (in San Benito County)

    "The county's mineral resources are diversified, but have remained largely undeveloped because of the lack of transportation facilities and possibly also because many deposits are on land held under agricultural patents by people not interested in mining.

    "Production of the following metals and mineral substances has been made in greater or less quantity: Antimony, asphalt, bituminous rock, bituminous coal, dolomite, gems, gypsum, lime and limestone, manganese, mineral water, rock, quicksilver, and petroleum. Quicksilver has given the county its reputation in the mining world. The county is the largest producer of mercury in the United States (circa 1915-1916). San Benito has the largest single producer of this class of material in the state. Limestone and lime were produced in some quantity from 1894 to 1907, but no production has been reported since, although the limestone resources are immense in quantity and of very high quality…."

    "…Dolomite deposits have been opened within the past year in the county (circa 1915-1916) and have yielded considerable amounts of a high-grade product to fill a Pacific coast demand.

    Cement (in San Benito County)

    "The deposits of limestone in this county which are suited for the manufacture of Portland cement are large, and are fairly well situated as regards mining and transportation. Particular mention is made of the larger deposits under the head of Limestone, and the reader will note, by reference to that section, that many of these beds are owned by large cement manufacturers. Only one corporation, however, has so far undertaken the erection of a cement plant in the county."

    Dolomite (in San Benito County)

    "Extensive bodies of a fine quality of dolomite are found southwest of Hollister in the lower hills of the Gabilan Range. The deposits are associated with the limestones mentioned previously, and show the effects of metamorphism due to intrusions and earth movements as observed at Gabilan Peak. Since the impetus given the steel industry in the past year, a limited demand has arisen on the Pacific Coast for dolomite, which is used in making refractory basic linings in open hearth steel furnaces. Dolomite has been shipped from two properties in San Benito County to Los Angeles and San Francisco. (See Baldi and Rothschild under the name of San Benito Quarries Co.)

    Lime and Limestone (in San Benito County)

    "Limestone suited for cement making and for burning occurs prominently along the Gabilan Range from San Juan Bautista to the region of Pine Rock. Some lime has been made for local use in several places in the region, but at present there is no production, nor has there been any for a period of about 8 years. Since the last report was prepared by this Bureau on San Benito County, a number of limestone properties have changed hands. Deposits formerly owned by M. Barbee, S. Lavagnino and A. F. Underwood, of San Juan Bautista, and Thomas Flint, of Hollister, are now held by the Old Mission Portland Cement Co. More detailed mention of these properties is made under the section on Cement,* in connection with a description of this company's other holdings."

    (* Please note: The section on Cement will not be included here.)

    Gabilan or Fremont Peak. This peak, and the adjacent ones, are composed largely of metamorphic limestones. Photo by S. D. Leman. Gabilan or Fremont Peak

    Stone Industry (of San Benito County)

    “Crushed rock and gravel are at present the only materials of this class handled in the county. Gravel is used only locally, but the rock-crushing plant operated at Logan supplies a wide market, both north and south.”

  • San Benito County Mineral Industry (circa 1919) – Excerpt from California Mineral Production for 1919, Bulletin No. 88, by Walter W. Bradley, California State Mining Bureau, 1920, pp. 159-160.

    Area: 1,392
    Population: 8,995 (1920 census)
    Location: West-central portion of state.

    "Although twenty-first among the counties of the state in regard to value of total mineral production, San Benito leads in one important branch of the mineral industry, namely, quicksilver.

    "Its other mineral resources, many of them undeveloped, include: antimony, bituminous rock, chromite, coal, gypsum, gems, limestone, mineral water, soapstone, and miscellaneous stone.

    "Commercial production for 1919 was as follows:

    (Headings for the information below are: Substance, Amount, and Value.)

    Dolomite, 7,000 tons, $24,500
    Quicksilver, 7,409 flasks, $668,989
    Stone, miscellaneous, ---, $164,300
    Other minerals,* ---, $418,687
    (Total value) $1,276,476

    (* Includes cement, magnesite, and mineral water.)

    San Benito County, 1916 Map, from California Mineral Production for 1919 (with County Maps), Bulletin No. 88, by Walter W. Bradley, California State Mining Bureau, San Francisco: California State Printing Office, 1920, pp. 195. San Benito County, 1916 Map
  • San Benito County, California, Mines and Mineral Resources (circa 1947) – Excerpts from "Mines and Mineral Resources of San Benito County, California," California State Division of Mines, California Journal of Mines and Geology, pp. Vol. 43, No. 1, January 1947, pp. 41-60. (Used with permission, California Department of Conservation, California Geological Survey.)

    San Benito County, by Charles V. Averill, Mining engineer, California State Division of Mines, Ferry Building, San Francisco. Manuscript submitted for publication January 1947.

    General Description of the County

    Introduction (to San Benito County)

    "San Benito County was created in 1874 from that part of Monterey County lying northeast of the Gabilan Mountains. An adjustment of the eastern boundary with Fresno and Merced Counties in 1887 increased the area of San Benito County to practically the present size and outline. Mission San Juan Bautista was founded in 1794, thrived until 1835, and was restored in 1888. Its walls still show original decorations painted by the Indians, and its long, arched corridors are still covered by the original tiles. The Mission faces a Plaza Square, which is maintained as a State Park. Other old buildings facing the square from two addition sizes form part of the park also. They have been restored and are open to the public.

    Geology (of San Benito County)

    "San Benito County lies about 100 miles south of San Francisco, extending southeastward from the Pajaro River for 70 miles. The average width is 20 miles. Except for Chittenden Pass, the Coast Range on the western boundary is unbroken, and through this pass sea breezes from Monterey Bay modify a climate which otherwise would be similar to that of the interior valleys. Temperatures in January range from about 36 to 58 F. and in July from 50 to 80 F. Average rainfall is 13.1 inches, 50 percent of which falls from December through February; summers are rainless.

    "According to the 1940 census, San Benito County had a population of 11,392, practically the same as in 1930. Like all other parts of California, the county has probably increased in population since 1940. The land area is 1,396 square miles.

    "Transportation is furnished by a branch line of the coast line of the Southern Pacific railroad operated between Gilroy in Santa Clara County and Hollister; also by State Highways 25, 152, and 180. Route 25 runs near the center of the county in a general north-south direction. Route 180 connects a point near the center of the county with Mendota, Fresno County, and Route 152 runs from points in the northern part of San Benito County eastward across the San Joaquin Valley to connect with Highway 99 near a point on the county line between Merced and Madera Counties. County roads, some with all-weather surface, reach various parts of the county.

    Topography (of San Benito County)

    "San Benito County is an area of valleys, hills, and mountains, almost bisected by the San Benito River, which flows northwestward near the center of the county. Elevations range from less than 100 feet at the Pajaro River in the north to 5,165 feet at the summit of San Benito Peak…."

    Geology (of San Benito County)

    "Detailed geology of the central part of San Benito County has been mapped by Wilson* in the San Benito quadrangle, a 15-minute sheet on a scale of 1:62,500 or approximately 1 inch to 1 mile. His report describes the geology and includes a bibliography of the geology of the surrounding region.

    (* Page 42, footnote 1: Wilson, I. F., Geology of the San Benito quadrangle, California: California Div. Mines Rept. 29, pp. 183-270, 1943.)

    "Taliaferro** has described the geology of the Central Coast Ranges including San Benito County. Two of his published sections run from the Pacific Ocean eastward entirely through this county to the San Joaquin Valley…."

    (** Page 42, footnote 2: Taliaferro, N. L., Geologic history and structure of the central Coast Ranges of California: California Div. Mines Bull. 118, pp. 119-163, 1943.)

    "Anderson and Pack*** examined the geology of the west border of the San Joaquin Valley in connection with possible petroleum production in 1909-11…Cretaceous and Tertiary sediments predominate in the region, but a large area of serpentine is shown south of the New Idria quicksilver mine, and small areas of basalt near Llanada."

    (*** Page 43, footnote 3: Anderson, Robert, and Pack, R. W., Geology and oil resources of the west border of the San Joaquin Valley north of Coalinga, California: U. S. Geol. Survey Bull. 603, p. 220, 1915.)

    "The geology of the Pinnacles National Monument has been described by Andrews.**** It is an area of rocky crags, caves, columns, pillars, and deeply carved canyons on the western boundary of San Benito County at a point 38 miles south of Hollister. The strange land forms are the result of erosion in a series of Miocene volcanic breccias. The map accompanying Andrews' report shows not only the volcanic formations but an equally large area of basement complex to the west in Monterey County, through which are scattered numerous lenses (0.1 mile, rarely 0.2 mile in diameter) of the Gabilan limestone."

    (**** Page 43, footnote 4: Andrews, Phillip, Geology of the Pinnacles National Monument: Univ. California, Dept. Geol. Sci., Bull. 24, pp. 1-33, 1940.)

    Industries (in San Benito County)

    "Of the total acreage of 893,440 in San Benito County, 733,094 acres or 82 percent are privately owned, and 698,056 acres are in farms. The total value of farm products in 1939 was $4,169,285. The most valuable agricultural products are beef cattle and calves, sugar beets, apricots, prunes, and tomatoes. Important field crops are barley, wheat, and hay. The cultivation of garden seeds brings an income of about $100,000 per year.

    "Manufacturing operations include food, processing and canning, preparation of feeds for animals, and the processing of garden and flower seeds.

    Mineral Resources (in San Benito County)

    "Mineral production ranks below agricultural production in San Benito County, but in 1943 reached a war-time maximum of $3,528,642. The important products were quicksilver, portland cement, and miscellaneous stone. Other mineral products are antimony, asbestos, asphalt, bentonite, chromite, coal, dolomite, gems, gypsum, lime, limestone, manganese, magnesite, and mineral water…."

    Lime and Limestone (in San Benito County)

    "Massive crystalline limestone suitable for manufacture of lime and cement and for other industrial purposes outcrops along the Gabilan Range from San Juan Bautista to the region around Pine Rock in T. 16 S., R. 8 E., M.D. In places the limestone is dolomitic. Only a few of the more important deposits are mentioned (in this report)…."

  • San Benito County Limestone Industry and Deposits (up to 1947) – Excerpts from "Limestone in California," by Clarence A. Logan, California Journal of Mines and Geology, Vol. 43, No. 3, July 1947, California Division of Mines, San Francisco, California, pp. 175-357. Used with permission, California Department of Conservation, California Geological Survey.)

    Limestone (in San Benito County)

    "Limestone and dolomite are plentiful in this county and considerable lime was burned many years ago. Lately the limestone produced has been used for making portland cement. Dolomite production started in 1915 and has been carried on intermittently. The limestone and dolomite are the oldest rocks of the region. They are found along the Gabilan Range from San Juan Bautista southeastward to the vicinity of The Pinnacles, an air-line distance of 24 miles. They are older than the pre-Franciscan Santa Lucia granite. The dolomite has been found on the lower slopes in those places where erosion has exposed it, and it can be seen to rest directly on decomposed granitic rock, or to be intruded by dikes and sills of such rock. Several of the dolomite deposits were described in 1915 (Bradley, W. W. 19, pp. 633-636).* The composition and physical character, including crystal form, show it to be a true dolomite but it may grade into dolomitic limestone within a short distance or show silicification near granitic contacts.

    "The removal of the railroad between Hollister and Tres Pinos has increased the length of the truck haul from many of the limestone and dolomite deposits. Hollister is the only feasible outlet for deposits south of that town."

    (* Walter W. Bradley and C. A. Logan, "San Benito County," California Min. Bur. Rept. 15, pp. 616-573, 1919)

    Dolomite (in San Benito County)

    "Probably the oldest rock in the county is the dolomite which occurs as part of the undifferentiated Gabilan limestone. These beds are older than the pre-Franciscan Santa Lucia granite, on which they lie.

    "Dolomite production began near Vineyard School in this county in 1915. It has been carried on intermittently by one or two producers who sold from 2500 tons to 18,000 tons a year. The use of dolomite during the last war for making magnesium and in the steel business stimulated the search for deposits in the region, and considerable prospecting and sampling of deposits in the county was done, although most of the war-time production in northern California was made from deposits in the western foothills of the Gabilan Range in adjoining Monterey County.

    "The roof pendants of limestone and dolomite are not shown on the San Benito County portion of the state geologic map (Jenkins, O. P. 38)* and so far as known to the writer have not been studied in detail. The dolomite deposits mentioned here are in the extreme northern part of the Gonzales quadrangle and the adjacent part of Hollister quadrangle. They occur at intervals from Monterey County east and southeast to the vicinity of Cienega School, so far as noted by the writer, who limited his inspection to that region because of the distance from the railroad. The deposits are along or near the San Andreas fault zone and have a vertical range of 800 to 2200 feet.

    (* Olaf P. Jenkins, Geologic map of California, scale 1:500,000, California Div. Mines, 1938)

    "Some of the deposits described in 1915 by the writer (Bradley, W. W. 19, pp. 633-636)* have passed into other hands and have lost their identities in the more extended prospecting which has resulted in the proving of larger deposits. Only one operator was active at time of visit.

    (* Walter W. Bradley and C. A. Logan, "San Benito County," California Min. Bur. Rept. 15, pp. 616-573, 1919)

    "When used in steel furnaces, a dolomite with less than 1 percent silica is preferred. For use in making magnesium, a minimum of 21 percent MgO was sought.

    "Cienega del Gabilan Rancho was a Spanish or Mexican land grant antedating American occupancy of California, and has not been covered by the public surveys, so that locations of deposits cannot be given by section. The deposits mentioned here are within the original boundaries of this grant 8 to 11 miles south of Hollister."*

    (* The dolomite deposits listed in the above section are listed in the list below according to locality, which is south of Hollister. Deposits listed are: Crowe Ranch dolomite deposit, A. E. Hamilton dolomite deposit, the Martin Ranch dolomite deposit, the O'Hara Ranch dolomite deposit, and the Permanent dolomite deposit.)

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