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Tuolomne County

  • Tuolumne County Stone Industry (circa 1890) - Excerpts from the Tenth Annual Report of The State Mineralogist For The Year Ending December 1, 1890, California State Mining Bureau, Sacramento: State Printing Office, 1890, pp. 734-736.

    Tuolumne County, by L. P. Goldstone, E.M., Assistant in the Field.

    “Tuolumne County is one of the principal mining counties of the State and covers an area of about two thousand square miles. Its east boundaries are the summits of the Sierra Nevada Mountains, from whence the decrease in altitude through the foothills of that range to the western boundary line is quite regular and gradual. The general topography of the county is necessarily quite rough and rugged, attaining, as it does, between its eastern and western boundary lines little besides hills and mountains....”

    “The geological character is varied. In many places it is volcanic the main feature of which is the extensive basaltic table land running for many miles through the county near to and bordering on the Stanislaus River. The eastern portion of the county is granitic in character with occasional dikes of porphyry and here and there cappings of basalt. The granite in many places gives evidence of its once plastic condition. The western portion of the county is made up of slate rocks, argillaceous siliceous, and talcose in character. Belts of serpentine cross north and south through the western slate formations, and for a long distance one of them runs parallel with and near to the west wall of the great gold bearing lode- the Mother Lode of California - which courses north about 35 degrees west through this county....”

    “The limestone formation that courses through the county from north to south is one of the most peculiar formations extant. It is very regular in width, varying from several miles at the northern part of the county to a half mile where it passes through the town of Sonora, its course being to this point nearly north and south; from here it courses southeast through the county, with an average width of from a mile to two miles. There are four distinct runs of slate coursing north through it, and they merge into two south of Sonora, and continue with the limestone until it reaches the county line, where the limestone has become denuded, either by the action of the elements or from the work of the thousands of miners who in years gone by placer-mined in the environs of Columbia, Springfield, Brown’s Flat, and Shaw’s Flat. In this immediate vicinity, the limestone is several miles in width. On approaching the scene from a point where the eye can take in a panoramic view, one is for a moment reminded of an inland sea, with its surface covered with white-crested waves; but on close inspection the formation shows itself in all possible and fantastic shapes. That the theory may be true that it was once the bed of a large sheet of water, highly impregnated with carbonic acid, and had eaten into the limestone, forming it as it is, I do not doubt. To my mind, a chemical action has undoubtedly taken place to form these shapes and crevices, varying in depth from a few feet to fifty and sixty feet, and no doubt much deeper, had not water prevented exploration; and that this chemical action is due more especially to the detritus and debris washed from the surrounding country, where the slates and country rocks are of varied character and highly mineralized. These have undoubtedly formed reactions with the limestone, and by the agency of flowing water of which undoubted signs are extant, and by these means Nature has carved these monuments to herself. The crevices and miniature caverns, through time, as they were formed, finally filled with this matter above referred to, which had carried with it gold, broken and disintegrated from the ledges of the surrounding country, and so were formed the richest placers ever discovered, which brought to ‘Old Tuolumne’ its first extensive influx of population, many of whom are still among its most prosperous citizens.

    • “There are several quarries of good marble and granite of superior texture and color in the county. Soapstone, or steatite, suitable for furnace lining, is also found in several localities; but beyond the local consumption, very little of the latter is used, their situation being so remote from the rail.”

  • Tuolumne County, Mines and Mineral Resources (circa 1913-1914) – Excerpts from Report XIV of the State Mineralogist – Mines and Mineral Resources of Portions of California, Chapters of State Mineralogist’s Report – Biennial Period 1913-1914, Part I. “The Counties of Amador County, Calaveras County, Tuolumne County,” by W. B. Tucker, Field Assistant, San Francisco, California, July, 1915, California State Mining Bureau, San Francisco, California, 1916, pp. 2-172.)

    Introduction

     Description (of Tuolumne County)

    “This county is bounded on the northwest by Calaveras County, on the northeast by Alpine and Mono, on the south by Mariposa, and on the southwest by Stanislaus.

    “Like most of the counties lying along the main gold belt, Tuolumne covers a portion of the foothills and the westerly slope of the Sierra Nevada, giving the whole county a rugged surface, and to the eastern portion a considerable altitude. A remarkable feature in the topography and geology of this county is the basaltic mesa known as Table Mountain, which, running near the parallel with its northwestern boundary, extends for a distance of nearly thirty miles. This formation consists of a lava flow, which, having filled the channel of an ancient river, stands now, through the degradation of the adjacent country, in isolated mass, its top nearly level and its sides nearly perpendicular – the former more than two thousand feet above the bed of the Stanislaus River, which breaks through it. Flowing through the county in a westerly direction is the Tuolumne River, with its three forks; also three forks of the Stanislaus River – all large streams – the main Stanislaus and its north fork forming in part the boundary between Tuolumne and Calaveras counties.

    “The county also has scores of lakes, among them Lake Eleanor, a beautiful body of water, which, with Hetch-Hetchy Valley, is one of the scenic wonders of the State. San Francisco aims to secure its entire water supply from the Tuolumne River.

    “Tuolumne County is not only well supplied with water, but is also abundantly timbered; the more elevated portions being covered with fir, pine, spruce and cedar, and the lower elevations with scrub oak and pine.

    While gold mining continues to be the leading industry (circa 1914), farming viticulture, fruit growing, lumbering and stock raising are here important and growing pursuits. The extensive limestone and marble deposits are being developed on a large scale, and the Columbia Marble Company, owner of the famous Columbia quarry, turns out a product that in beauty, durability and susceptibility to a brilliant polish, is the equal of any other in the United States.

    Power Plants (in Tuolumne County).

    Tuolumne Water Power Company. This property consists of storage reservoirs on the South Fork of the Stanislaus River, main and distributing ditches, and small distributing reservoirs.

    “The generating station is operated under a static head of about 1000 feet; the four generators of 2500 horsepower capacity are driven by four direct-connected Pelton water wheels, and the power is transmitted by about 30 miles of transmission lines to the principal towns and mines operated by electrical energy. The company also maintains about 85 miles of ditches for mining and agricultural purposes.

    “Stanislaus Electric Power Company. This power plant on the Stanislaus River generates electric power to operate the street car system of the United Railroads in San Francisco and other cities, while at the same time furnishing lights and power to many places, including towns and mines of this county. The main reservoir, at Relief, has a storage capacity of 550,000,000 cubic feet of water. The electric plant generates 35,000 horsepower.

    Railway Facilities (in Tuolumne County).

    “The county has the advantage of direct communication with Stockton by means of the Southern Pacific Railroad to Oakdale, thence over the Sierra Railroad to Jamestown, where one branch runs to Angels Camp, Calaveras County, the other to Sonora and Tuolumne City, the last named being the terminus of the road.

    Wagon Roads (in Tuolumne County).

    “Considering the rough character of the country in the county, the roads from the railroad points to the different mining districts are better as a whole than those of any other territory similarly situated.

    Mineral Resources (in Tuolumne County).

    “The mineral resources of Tuolumne County consist of chrome, copper, gold, lime, limestone, marble, mineral paint, platinum, soapstone, silver, stone industry, sulphur.

    Mining Conditions (in Tuolumne County).

    “There is an increased activity in mining operations in Tuolumne County (circa 1914), especially on the Mother Lode belt in the neighborhood of Jamestown, where extensive operations are being carried on at the Jumper, Dutch, and Harvard mines, and the prospects look bright for the reopening of the App and Rawhide mines, which were famous producers in the past. In the neighborhood of Jacksonville, the Eagle Shawmut mine, after a year’s shut down for the installation of electric hoisting and underground tramway equipment, has resumed operations on an extensive scale, and will handle a larger tonnage than ever. On the east belt, in the granodiorite area in the Soulsbyville district, the wonderful showing of the Black Oak mine (which, through its modern cyanide plant has successfully demonstrated the treatment of the base ores of this district), has caused a renewal of interest in this belt by mine operators, as several old and new properties are being reopened.

    “In the neighborhood of Tuolumne there is a notable revival in mining, as the New Albany and Providence mines have resumed operations and promise to be steady producers.

    “Increased activity is being shown in pocket mining on Jackass Hill, near Tuttletown, and on Bald Mountain in the neighborhood of Sonora and Columbia.

    “Owing to the large amount of rain during the past year (circa 1914), a great number of gravel mines have reopened, and there should be a great increase in production from this source of mining. An extensive amount of development is under progress on the ancient river channels of Table Mountain, especially notable being the driving of a 6000-foot tunnel by the Springfield Tunnel and Development Company at Columbia, which if successful will mean a boom for this famous old camp as a gold producer.

    “In this county there still remains a large area of unexplored territory, on both the central and east belts, which only wants the capital to open up new producing mines.”

    The following information is taken from the table on the insert page after page 132 entitled, “Tuolumne County – Table of Mineral Production.”

    Lime Production in Tuolumne County:

    1903: 1,600 barrels; Value: $1,600.
    1905: 500 barrels; Value: $1,000.
    1906: 500 barrels; Value: $1,000.
    1907: 110,000 barrels; Value: $125,000.
    1908: 60,000 barrels; Value: $69,500.
    1909: 60,000 barrels; Value: $60,000.
    1910: 78,300 barrels; Value: $78,300.
    1911: 13,243 barrels; Value: $70,000.
    1912: 25,146 barrels; Value: $121,250.
    Totals: 578,350 barrels; Value: $612,650.

    Limestone Productionin Tuolumne County:

    1908: 1,233 tons; Value: $6,500.
    1909: 15,057 tons; Value: $28,942.
    1910: 3,600 tons; Value: $10,400.
    1911: 4,319 tons; Value: $13,609.
    1912: 11,554 tons; Value: $20,099.
    1913: 12,446 tons; Value: $20,676.
    Totals: 48,209 tons; Value: $100,226.

    Marble Production in Tuolumne County:

    1902: 7,000 cubic feet; Value: $14,000.
    1903: 11,550 cubic feet; Value: $28,875.
    1904: 11,500 cubic feet; Value: $28,750.
    1905: 11,000 cubic feet; Value: $66,000.
    1906: 23,000 cubic feet; Value: $46,000.
    1907: 22,030 cubic feet; Value: $60,120.
    1908: 18,503 cubic feet; Value: $47,165.
    1909: 27,600 cubic feet; Value: $107,400.
    1910: 17,360 cubic feet; Value: $45,400.
    1911: 18,966 cubic feet; Value: $50,398.
    1912: 27,720 cubic feet; Value: $73,920.
    1913: 37,312 cubic feet; Value: $93,726.
    Totals: 233,541 cubic feet; Value: $661,754.

    Granite Production in Tuolumne County (listed under the “Miscellaneous and unapportioned” section):

    1903: 10,367 cubic feet granite; Value: $14,020.
    1904: 9,700 cubic feet granite; Value: $9,700.
    1905: 9,700 cubic feet granite; Value: $9,700.
    1906: 9,700 cubic feet granite; Value: $9,700.

    Total mineral production of Tuolumne County from 1880 to 1913, inclusive (Stone only):

    Lime: $612,650
    Limestone: $100,226
    Marble: $661,754
    Stone industry: $48,448
    (“Stone industry” includes granite)
    Totals: $34,744,511
  • Tuolumne 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. 170.
    Area: 2,190 square miles.
    Population: 7,768 (1920 census).
    Location: East-central portion of State-Mother Lode district.

    “Tuolumne ranks twenty-seventh among the counties of the state relative to its total value of mineral output. As a producer of marble its standing is first. The decrease in 1919 to $459,396 from the 1918 figure of $602,278 was due to chromite.

    “Chromite, clay, copper, gold, lead, limestone, marble, mineral paint, platinum, soapstone, silver, and miscellaneous stone, are among its mineral resources.

    “Commercial production for 1919 was as follows:

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

    Gold, ---, $250,000 (estimated)
    Lime and limestone, ---, $110,746 (estimated)
    Silver, ---, $17,000 (estimated)
    Stone, miscellaneous, ---, $2,700
    Other minerals.* ---, $78,950
    Tuolumne 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. 188. Tuolumne County , 1916 Map
  • Tuolumne County Limestone and Marble 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.)

    “Considering its extent and its potential importance, the great series of deposits in Tuolumne County appears to have received comparatively little attention from geologists. The Big Trees folio of the U.S. Geological Survey does not show a single analysis of the stone, and makes no reference to the differing character of the limestone in different beds. It is an interesting fact, brought out by sampling in connection with field work for this report, that wide beds of high-grade stone, ranging from high-calcium, low-magnesium limestone to nearly true dolomite, occur close together in different parts of the district. A detailed study would probably bring out many interesting facts about this greatest of northern California’s limestone accumulations. The period over which deposition extended must have been a long one, but it is doubtful if its length could even be estimated approximately because of the amount of folding that has probably gone on and the obliteration of fossils and bedding by the pressure exerted, which has nearly everywhere changed the limestone to marble.

    “While there are many hundreds of acres of land in and around Sonora, Columbia, and Springfield where limestone and marble have been exposed, much of this land is in residence or farm properties having value that would prevent consideration as sources of limestone. These are not covered in the present report, in which the effort has been made to give a comprehensive idea of those parts of the main limestone belt which are on or near good roads within 10 miles of the railroad.

    “The district has been noted particularly for the production of marble but the last of the quarries was closed down several years ago and marble-working equipment has been removed from both quarries (circa 1947). There is an abundance of high-grade marble in this county which takes a good polish and has been shown to excel in physical properties many of the marbles which are brought long distances for use in the Pacific Coast market. The quarrying, cutting, and polishing of marble are expensive, and the percentage of waste is always high. The marketing of this waste is an important item to the marble producer, and if he has facilities for selling it or converting it into salable product, this may help him to stay in business.”

  • Tuolumne County Mines and Geology (circa 1949) – (Excerpts from “Mines and Mineral Resources of Tuolumne County, California,” by Clarence A. Logan, California Journal of Mines and Geology, Vol. 45, No. 1, January 1949, pp. 47-83. Used with permission, California Department of Conservation, California Geological Survey.)

    “Mines and Mineral Resources of Tuolumne County, California,” by Clarence A. Logan, District Mining Engineer, Sacramento District, California State Division of Mines. Manuscript submitted for publication July 15, 1948.

    Abstract

    “Tuolumne County, one of the Mother Lode counties, extends from the eastern border of the Central Valley to the higher peaks of the Sierra Nevada, including San Francisco’s Hetch Hetchy water system and part of Yosemite National Park. The Mother Lode highway gives road connection with Calaveras County on the north and Mariposa to the south. Two other state highways, one through Yosemite Park, extend from the west across the mountains to Nevada. Sierra Railroad gives a broad-gauge outlet for freight to main lines at Oakdale.’

    “The county owes its early reputation as a gold-producer to the immensely rich placers of Columbia and Springfield, where $55,000,000 in gold was mined from shallow deposits in potholes and crevices of the limestone bedrock prior to 1899. The pocket mines of Sonora, Bald Mountain and vicinity have also been highly productive and exceptionally long-lived. No similar area anywhere has produced as much gold from comparable depths….”

    “Marble and limestone products have been next to gold in value. The Columbia marble beds had a long history of production prior to 1941, and two plants are at present processing the stone from these deposits.

    “In common with the other counties along the western slope of the Sierra Nevada, Tuolumne contains deposits of chromite, copper, soapstone, scheelite, and slate. Magnesite has been produced and other metallic and nonmetallic minerals have ben noted or have been shipped in small quantities….”

    Geography (of Tuolumne County)

    “The part of Tuolumne County of principal interest to the miner is the westernmost one-third extending to the east line of Range 16 East, M. D. The three forks of Stanislaus River drain the northern part, and the southern half of the county includes the entire drainage basin of Tuolumne River. The easterly one-third of the county is within Yosemite National Park State highways from the west enter from Knights Ferry and Melones, both on Stanislaus River, which forms the west boundary. These and connecting country roads give access to most of the mining districts. Lumbering is the principal industry. Sonora, the county seat, is at an elevation of about 1900 feet at the junction of two paved highways. Railway service to the Mother Lode mines, to Sonora and lumber towns to the east is given by Sierra Railway of California which connects with the Southern Pacific Railroad at Oakdale, Stanislaus County. Little snow falls below the 2000-foot level. The dry season extends usually from May to November; most of the rainfal occurs during the first three or four months of the year. Summers aredevoid of rain in the mining region, and in the southwestern section of the county where the elevation is only a few hundred feet above sea-level, daytime temperatures may be high, but cause no distress because of the low humidity.

    “Timber, water, and electric power are available generally in the mining districts.

    Mineral Resources (of Tuolumne County)

    “Gold, marble, and limestone have been the leading mineral products of Tuolumne County. Much of the limestone is dolomitic and some of it has been commercially classed as dolomite and so reported. Chromite, copper, clay, granite, magnesite, miscellaneous stone, soapstone, and slate have been produced, and in the sixties graphite was mined ad shipped to England. Some by-product lead and silver from gold-quartz ores, and platinum found in placer gold, have also been reported. Chrysotile and amphibole asbestos, and diatomite occur within the county.”

    Plate 7-A. Tuolumne-Calaveras Counties Marble Deposit. View northwest from Columbia. The canyon of Stanislaus River extends across the region in the middle distance. Tuolumne-Calaveras Counties Marble Deposit
    Plate 7-B. Limestone Bedrock. Exposed by early placer mining near Columbia. Limestone Bedrock. Exposed by early placer mining near Columbia

    Limestone and Marble (in Tuolumne County)

    “The limestone beds, altered to marble, which extend from the vicinity of Murphy in Calaveras County southward through Columbia and Sonora are 2 miles wide north of Columbia. In that region they have been closed. At present (circa 1949), marble is being crushed in one lant for making terrazzo, and one property is supplying stone to the kilns of U.S. Lime Products Company a mile south of Sonora, where an underground mine is also producing limestone. What as undoubtedly once a continuous belt of limestone has been broken for a distance of about a mile north of Curtis Creek by a granitic intrusion and later erosion. From Curtis Creek 4 miles south of Sonora, the limestone continues southward for a mile and then turns east, extending 8 miles, into the canyon of the Middle Fordk of Tuolumne River.

    “The limestone and marble resources of this county have been described in numerous analyses, in a recent report of the Division of Mines* and will be only summarized here.

    (* Page 76 footnote 13: Logan, Clarence A., Limestone in California: California Jour. Mines and Geology, vol. 43, pp. 341-348, 1947.)

    “The marble near Columbia, Springfield, and Shaws Flat was uncovered by the placer miners who found rich deposits of gold in the thin layer of soil and gravel which originally mantled it. The rough surface of the limestone, full of shallow pits and solution cavities, made a good riffle for gold. Marble quarrying began near Sonora in 1860 and continued off and on until 1942. The product was of superior quality and the district was the most important source of marble in the state. The supply of marble here is immense, and working conditions are favorable. However, marble, granite, and sandstone used for building construction require a great deal of expensive skilled labor, and none of them has been able to compete with clay products and concrete, except for interior work, where California marble has had competition from marble from other states and from foreign countries.

    “This marble generally contains considerable magnesium, but not sufficient to be properly called dolomite, so far as available analyses indicate. It is dense and hard, taking a fine polish and having a compressive strength of 25,000 pounds per square inch. The weight is 169 to 182 pounds per square inch. The principal production has been a white, fine-grained marble with blue veining, although other shades to nearly black, including a beautiful buff stone with reddish veining, called Portola marble, have been produced from the Columbia quarry.

    “Except for the operations of U. S. Lime Products Company 1 mile south of Sonora, there is no activity in the southern part of the limestone belt at present. In a recent report** the writer has shown that high-grade limestone, varying in composition from high-calcium stone with minor impurities, to nearly true dolomite, occurs there in large deposits.”

    (** Page 76, footnote 14: Logan, C. A., Limestone in California, California Jour. Mines and Geology, vol. 43, 1947, pp. 341-348.)

    Slate (in Tuolumne County)

    “A belt of Mariposa (Jurassic) black clay-slate strikes northwest across the west side of the county. A quarry was operated on this slate near Hetch Hetchy Junction (also known as Rosasco) from 1931 to 1940. It is in sec. 36, T. 1 S., R. 13 E. within 200 feet of the tracks of the Sierra Railroad. A crew of five men produced at the rate of about 500 tons a month for part of the above period. The slate was shipped to San Francisco by Walter S. McLean. It was crushed to make roofing granules for ‘ready roofing’ and dust was said to be utilized as filler in a coarse grade of paper used for lining refrigerator cars.

    “In 1941, Walter C. Sundberg, Sonora, sold some slate for flagging.

    Soapstone and Talc (in Tuolumne County)

    “Soapstone and talc have been found at several places in the county but the only sales reported were of soapstone in 1931-32, from near Jamestown. It was used locally in earlier days for chimneys and buildings. Talc outcrops have been reported at Shaws Flat, on Yankee Hill, and near Shawmut. Soapstone has been noted in the Moccasin district 2 miles from the Hetch Hetchy Railroad, near Crimea House 2 miles east of the Sierra Railroad, and probably at several other points, as in past years several persons have listed deposits or tonnage for sale without stating the location. Outcrops of serpentine are numerous, as mentioned under Chromite, and soapstone may be expected in this serpentine. In the region of the dolomitic limestone, however, there is a possibility of talc occurrence although no description of such a deposit has been noted for Tuolumne County.

    Stone Industry (in Tuolumne County)

    “Beerman & Jones, Sonora, have been listed for many years as producers of crushed rock at Soulsbyville. Use has also been made at times of waste marble from the Columbia district for road work.

    “Two small ‘granite’ quarries were operated 25 years or more ago. The stone they produced is a granodiorite of medium texture and pleasing bluish gray color.”

  • Tuolumne County Limestone Belt (circa 1949) – Excerpts from “Geology of Limestone near Sonora, Tuolumne County, California, Journal of Mines and Geology, Vol. 45, No. 4, October 1949, Centennial Issue, State of California Division of Mines. (Used with permission, California Department of Conservation, California Geological Survey.)

    Introduction

    “A belt of crystalline limestone containing discontinuous layers of schist extends northwest through the town of Sonora, Tuolumne County, California. The most extensive limestone area is adjacent to Black Leg Creek, approximately three-quarters of a mile southeast of the town of Sonora. The belt is approximately 2 miles long and near its north end is nearly 2,000 feet wide. Some limestone zones in the belt are commercially valuable because they are composed almost wholly of calcium carbonate, but most of the limestone contains too much magnesium carbonate. All the limestone is crystalline, ranging from moderately fine grained to moderately coarse grained….”

    Limestone Deposits – Lithologic and Chemical Characteristics (in Tuolumne County)

    “All the limestone within the area studied is crystalline, and grains are large enough to be readily seen with the unaided eye. Typical of the limestone is its banding. The bands are a fraction of an inch to several inches thick, and they consist of more or less parallel, alternate layers of dark-gray and pale-gray or white limestone. These bands are parallel to the boundaries of lithologic units and may be either bedding or the result of flowage during folding. Locally, differential weathering along the bands makes the layering conspicuous. In most places, however, the weathered limestone is characterized by the irregularity of solution pits and solution channels….”

    “The limestone is of two major types: (1) those made up chiefly of calcium carbonate (CaCO3) and containing not more than 5 percent of other substances; and (2) those containing an appreciable amount – 5 to 30 percent – of other substances, mostly magnesium carbonate (MgCO3). In general, these two types can be distinguished in the field by the marked difference in grain size. The magnesian limestone is finer grained, most of the individual grains ranging in diameter from 0.05 to 0.3 of a millimeter. In the limestone composed of nearly pure calcium carbonate, the grains range from 0.5 to 5 millimeters.

    “Most of the high-calcium limestone is found along two zones in the belt, which otherwise consists mainly of magnesian limestone. The zone being mined at present is close to the east side of the belt, near Sullivan Creek….”

    Economic Geology (of Tuolumne County)

    “In 1947 limestone was exploited only at the U. S. Lime Products Corporation mine, located in the central part of the area, about a mile south of Sonora. Six limestone quarries in the belt were idle…, and many other sites favorable for quarrying operations have never been developed. The mine of the U. S. Lime Products Corporation consists of a vertical shaft with levels at 120, 170, 215, 265, and 320 feet. Two wide zones of high-calcium limestone were being mined, and a third zone which lies immediately west of these has been worked in the past. Mining was by the room-and-pillar method; underground, most of the rock is moved by slushers and in chutes. A large processing plant is adjacent to the shaft collar. The products shipped include both crude and calcined varieties of high-grade limestone and low-iron dolomite. The leading produce in 1947 was limestone for glass manufacture….”

    “In summary, the Sonora limestone belt is favorable for the production of high-quality limestone for industrial purposes. High-calcium and magnesian limestone is available in ample quantities. In the large-scale mining of limestone of chemical grade, however, avoidance of dikes and magnesia-rich zones is necessary. Markets are close at hand and transportation is good.”

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