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  • El Dorado County Mines and Mineral Resources (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 III. The Counties of El Dorado, Placer, Sacramento, Yuba, California State Mining Bureau, 1919, pp. 271-459. (Used with permission, California Department of Conservation, California Geological Survey.)

    El Dorado County, by W. Burling Tucker, Field Assistant. Field Work in December, 1914.


    The following report represents only a little over a month's field work in the county, as owing to the season of the year, the north and eastern sections of the county were covered with snow. Hence, it was impossible to investigate the more remote mining districts; but, by combining the writer's personal observations on the principal properties with other data from reliable sources, all deposits of any importance have received attention, and are accurately recorded.

    Description (of El Dorado County).

    "El Dorado County has the distinction of being the scene of Marshall's discovery of gold at Coloma, and the earliest beginning of the modern era of gold mining.

    "El Dorado County is bounded on the north by Placer, on the south by Amador, on the east by Alpine County, and the state of Nevada, and on the west by Sacramento and Placer counties. The Middle Fork of the American River separates this county from Placer, while the Cosumnes separates it from Amador County. These rivers, with their numerous branches, constitute the principal streams found in El Dorado County. In the eastern part of the county at an altitude of about six thousand feet, a number of lakes occur; Lake Tahoe, the most important body of fresh water in California, being partly in this county, and is one of the scenic wonders of California.

    "Three-fourths of this county, including the more mountainous parts, are heavily wooded, the timber consisting of stately forests of pine, spruce and cedar. The balance is covered with a more scattered growth of oak and inferior pine, there being very little timber of any kind in the extreme western portion of the county.

    Power (in El Dorado County).

    "Electric power is furnished to the mines by the Western States Power Company, and water by the San Francisco-Oakland Terminal Power Company.

    Transportation Facilities (in El Dorado County).

    "From San Francisco and other important trade centers, this county has the benefit of good railroad communication by means of the Southern Pacific Railroad to Sacramento, from which point a branch line of the same system over the Sacramento and Placerville Railroad to Placerville passes through Shingle Springs, El Dorado and Diamond Springs, with terminus at Placerville.

    Roads (in El Dorado County).

    "The main state highway, which is at present under construction (circa 1915), runs from Sacramento via Folsom and Placerville to Lake Tahoe and Carson City, Nevada, the proposed route running directly east through the center of the county. The principal mining districts are in easy communication by means of good wagon roads with different railway points.

    General Geology (in El Dorado County).

    "The western margin of the county is followed by a belt of the Calaveras formation, greatly broken by later intrusions and in part accompanied by greenstone tuffs of the Carboniferous age. The late Jurassic, Mariposa formation, accompanied by large masses of greenstones and greenstone tuffs, traverses the western area in a narrow band from north to south. East of these rocks the Calaveras formation, having a prevailing northerly trend, occupies the greater eastern part of the county. A large area of gabbro-diorite lies near the western margin; numerous serpentine areas of elongated form are found in the same vicinity.

    "Gabbro, gabbro-diorite and serpentine belts traverse the county along a line from about one mile east of Placerville to a mile east of Georgetown.

    "The main granitic area of the high Sierra makes up the eastern part of the county. Tertiary auriferous gravels are exposed near Placerville. Rhyolitic tuffs lie in the old stream beds on the Long Cañon divides. Andesitic tuff-breccias cap many of the ridges from the Cosumnes to Long Cañon, but the largest masses are found on the Placerville and Newtown divides.

    Mineral Production (in El Dorado County).

    "The principal mineral resources of El Dorado County, many of them undeveloped, are: Asbestos, Barytes, Chromite, Clay, Copper, Gems, Gold, Iron, Molybdenum, Limestone, Quartz Crystals, Quicksilver, Glass-sand, Slate, Soapstone, Silver and Miscellaneous Stone."

    In the table on page 273 entitled, "El Dorado County - Mineral Production,"* the years covered by the table range from 1880 to 1915, although the value of stone production did not start until 1894. For the years from 1894 until 1915, the table shows the total values for the stone industry in El Dorado County: barrels of lime: 257,817, valued at $243,444; the tons of limestone produced is blank, but the value for limestone is given as $22,343; squares of slate produced: 58,611 for a value of $481,910; Stone Industry value: $29,364.

    (*This table will not be presented in this document.)

  • El Dorado, County, California, Mineral Resources & Introduction to the El Dorado County Area of California (circa 1915) - Excerpt from Sacramento Valley and Foothill Counties of California: An Illustrated Description of all the Counties Embraced in this Richly productive Geographical Subdivision of the Golden State, compiled and edited by Emmett Phillips and John H. Miller, Published under the direction of The Sacramento Valley Exposition, J. A. Filcher, Director-in Chief, January, 1915.

    El Dorado County

    "From a historical standpoint, El Dorado will always be one of the most interesting counties of California, for it was here that James Marshall discovered gold in a mill race at Coloma on the American River in 1848, and for the first time directed the attention of the world to this land of wonderful resources. In the early days of California's history, El Dorado was the scene of many deeds which have been vividly pictured by some of the best writers of American literature. One of the main overland roads across which the pioneers came upon entering California in their ox teams from the East, leads directly to Placerville, the county seat, in the early days known as Hangtown, which was one of the liveliest of all mining towns in the '50s.

    "But it is not from historical interest alone that El Dorado is attracting attention to-day. The county is exceedingly resourceful and offers just as good or better opportunities to settlers in 1915 as it did to fortune hunters in '49. The principal industries of the county are mining, fruit raising, lumbering, stock raising and general farming. In all of these branches of endeavor there are excellent opportunities for development, as land is to be had for a reasonable price in El Dorado and there is abundance of water for irrigation. For certain products soil and climatic conditions are unexcelled and the husbandman who plants Bartlett pears, plums, prunes, apples, peaches, olives and walnuts is sure of success. Oranges are grown in the western part of the county. All of these fruits have been tried and found profitable year after year for the grower. The Bartlett pear grown in El Dorado County cannot be excelled. Prices realized in Eastern markets for all El Dorado fruits are the very highest. This county was the first to adopt the standard pack, which assures quality of the first class to the purchaser.

    "Being a foothill and mountain county, the products of El Dorado do not ripen as early as those in the counties in lower altitudes on the floor of the Sacramento valley. This fact is not a disadvantage, as it might at first seem, but a decided advantage to the El Dorado grower, because his fruits come upon the market after the valley crops of the same varieties have been harvested and marketed. Hence, the mountain products do not meet with competition.

    "Unimproved land in El Dorado County can be purchased for from $20 to $80 an acre (circa 1915). In most cases it is covered with a growth of timber, which has to be cut before cultivation can be started. This in most cases does not add to the cost of the land, as the cut timber can be sold and it pays a large portion of the cost of clearing. The soil is rich sandy loam and decomposed lava, a gray volcanic rock. Most of the soils are formed by the disintegration of slate and allied rocks. They are deep and well drained and readily retain moisture.

    "There is abundance of water for irrigation in El Dorado, derived from the American River on the north and the Cosumnes and its tributaries on the south. These streams rise in the higher altitudes of the mountains and flow in a general westerly direction through deep canyons to the valley lands below. Not only do they supply water for domestic purposes to towns and cities for irrigation of money-making farms, but they offer unlimited opportunities for electric power development. There are now several power plants in El Dorado, where electricity for many uses is generated.

    "Since early days the mining industry has been one of great importance in El Dorado and it will probably continue so for many generations to come. The county lies on the 'mother lode' or rich ore vein which extends through several counties on the western slope of the Sierra Nevada Mountains. In the first few years following the discovery of gold, all the streams of the county were 'worked over' with the sluice and rocker, the crude method followed by the pioneers in seeking gold. Later, deep mining on modern scientific lines was introduced and is now followed. El Dorado County has produced upwards of $150,000,000 in gold from gravel alone and the source of this supply lying in the higher regions northeast and southeast of Placerville, has as yet been only partially explored.

    "The precious metal is not the only mineral product of the county. There are large deposits of slate, granite, lime, asbestos and other building stones and some diamonds have been found.

    "The lumbering industry of El Dorado gives employment to hundreds of workmen and distributes thousands of dollars in wages annually. The trees cut for commercial purposes are coniferous and the wood is soft. The most important kinds are the sugar and the yellow pine, the Douglas spruce, the cedar and two varieties of fir.

    "There are several large lumber mills in the county. One of these is located at Pino Grand, 25 miles northeast of Placerville, and is reached by a narrow gauge railroad from Camino. At Camino are situated the lumber yards and box factory of the company.

    "The California Door Company's mill is located at Calder and is reached by a narrow gauge railroad from Diamond Springs, with the lumber yards at the latter place.

    "El Dorado is also a resort county. Some of the most popular Summer resorts in California are found within its borders (circa 1915). This is particularly true of the higher altitudes of the Sierra Nevadas, where lakes and streams are numerous and fish and game are plentiful. El Dorado County, it should be added, extends over the summit of the Sierra Nevada Mountains to the boundary line of Nevada. It is approximately seventy miles long and thirty-five miles wide. About two-thirds of the total area of Lake Tahoe, one of the most celebrated mountain lakes in the world, and a spot that delights thousands of pleasure seekers during the Summer months, lies in El Dorado County. Trout of many varieties abound in the mountain streams, and game, such as bear, deer, rabbit, grouse and mountain quail, is plentiful.

    "The State Highway, which will be the Lincoln Highway (circa 1915), leads from Sacramento to Lake Tahoe and passes through the full length of El Dorado County from west to east. This is one of the famous scenic highways of California. Delightful resorts are numerous along this road, which follows the course of the south fork of the American River. Good trout fishing is to be had at almost any point in this stream.

    "The county seat of El Dorado is Placerville. It is a progressive city with good schools, the county high school being located there.

    "The average rainfall of the county is from 40 to 60 inches."

  • El Dorado 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. 146.

    Area: 1,753 square miles.
    Population: 6,426 (1920 census).
    Location: East-central portion of the state, northernmost of the Mother Lode counties.

    "El Dorado County, which contains the locality where gold in California was first heralded to the world, comes thirty-ninth on the list of counties ranked according to the value of their total mineral production during the year 1919. In addition to the segregated figures here given, a large tonnage of limestone is annually shipped from El Dorado for use in cement manufacture, and whose value is included in the state total for cement. Chromite and limestone both showed important decreases for 1919.

    "The mineral resources of this section, many of them undeveloped, include asbestos, barytes, chromite, clay, copper, gems, gold, iron, molybdenum, limestone, quartz crystals, quicksilver, glass-sand, slate, soapstone, silver and miscellaneous stone.

    "Commercial production for 1919 was as follows:"

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

    Chromite, 378 tons, $6,510
    Gold, ---, $28,000 (estimated)
    Limestone, 41,025 tons, 112-423
    Silver, ---, $700 (estimated)
    Soapstone or talc, 1,600 tons, $13,950
    Stone, miscellaneous, ---, $1,700
    Other minerals, ---, $1,169
    (Total value) $164,452

    El Dorado 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. 186. El Dorado County , 1916 Map
  • El Dorado County Limestone Industry and Limestone Deposits - Excerpt 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.)

    "El Dorado County contains some of the largest high-calcium limestone deposits in northern California, located within a few miles of railroad, and will probably remain as it was in the past, one of the principal sources of such stone. In 1936 El Dorado County produced over half all 'industrial' limestone marketed in the state. In 1941, work at the largest producer, Mountain Quarries, was stopped, but announcement has just been made that the owners of another property will begin work at a deposit in the same district on the north side of the county this year (circa 1947). Operation of another deposit near Rattlesnake Bar, formerly worked by Auburn Chemical Lime Company, is also announced and both of these will probably be well under way before publication of this report, giving four active properties. For many years prior to the exploitation of shell deposits in South San Francisco Bay, Mountain Quarries furnished 1000 tons or more of limestone a day which was shipped to a cement plant then operated at Cement, Solano County, but since closed. Thereafter, the quarry was a large seasonal producer of limestone for other industries.

    "The limestone deposits form part of the Carboniferous beds locally called the Calaveras formation. The differentiation of the Carboniferous has not been worked out in this region. The assignment to the Carboniferous was made on the basis of limited fossil evidence, as the limestone and the beds with which it is associated have undergone such intense dynamic metamorphism that little such evidence has survived. The limestones in western El Dorado are thoroughly crystallized as a result of the pressure, and stand usually as nearly vertical lenses with their longest dimension striking nearly north. There is often little evidence of the originally sedimentary rocks, such as slate, chert, and quartzite, to be expected normally with them. The prevailing wall rock in which the limestone is encased has long been known and mapped as amphibolite schist. It is believed that the layers of such rock containing the limestone should be called para-amphibolite schist, to indicate its probable derivation from sediments or from volcanic ash which either settled as dust from the air upon the ocean or was interbedded with the limestone by sedimentation. Otherwise, it is hard to explain the absence of evidence of contact metamorphism such as wollastonite, garnet, or other calcium silicates, or sharply marked variations in crystal size and degree of silicification of the limestone (or marble) itself. Several or all such phenomena are to be observed in limestone in regions invaded by igneous rocks."

  • El Dorado County Dimension Stone, Dolomite, Limestone, Slate, and Soapstone (historical account leading up to circa 1956) (From "Mines and Mineral Resources of El Dorado County, California," California Journal of Mines and Geology, Vol. 52, No. 4, October 1956, California Division of Mines. Used with permission, California Department of Conservation, California Geological Survey.)

    El Dorado County Dimension Stone

    "Dimension stone was quarried in El Dorado County starting soon after the beginning of the gold rush. A number of buildings in Placerville, El Dorado, Diamond Springs and Shingle Springs, Coloma, and Lotus were constructed of rhyolite tuff, granite, and greenstone during the 1850's. Also there are many early-day stone walls and fences in the western portion of the county. Much of the stone used in these structures was quarried locally.

    "Rhyolite tuff of Miocene age was the most widely used stone for these early structures. Some was imported from the Volcano area of Amador County. Greenstone of the Calaveras and Amador groups, granite, and smaller amounts of serpentine, limestone, and talc schist also were used. Large quantities of boulders of andesite of Mio-Pliocene age were used to construct fences, walls, and miners' dams. Many of these were built by Chinese laborers.

    "In later years the demand for dimension stone for building purposes decreased. However, since 1947, rhyolite tuff has been quarried and processed in a plant in the Newtown area and marketed under the trade name Sierra Placerite as ornamental stone for use in patios and fireplaces. Also small amounts of rough flagstone composed of rhyolite tuff have been produced intermittently in the Newtown area for the past several years.

    El Dorado County Dolomite

    "A vein of dolomite occurs at the Larkin gold mine, which is 1 mile west of Diamond Springs. This vein, which is as much as 42 feet in width at the surface, is part of the Mother Lode system (Logan, 1947, p. 233). The dolomite has a rusty color because of the presence of iron oxide. Talc, quartz, and pyrite are also present.

    El Dorado County Limestone

    "For many years the production of limestone and lime has been a major industry in El Dorado County. At present lime and limestone are the chief mineral products of the county. The Cool-Cave Valley limestone deposit, the largest in the county, was a major source of limestone for a cement plant in the San Francisco area for nearly 30 years (Clark, 1954, p. 440). Four producers supply limestone for use in lime manufacture, sugar beet refining, glass manufacture, steel fluxs, roofing granules, poultry grits, mineral filler, aggregate material, and soil conditioners. Lime-manufacturing plants are active at two of the properties. Much of the finished material is marketed in the San Francisco and Sacramento-Stockton areas.

    "Some of the largest accessible limestone deposits of the Sierra Nevada are in the county. Many have been worked at one time or another. All of the deposits are composed of fine- to coarse-grained crystalline limestone that ranges from white to bluish-gray in color. On the basis of limited fossil evidence, the limestone is considered to be of Carboniferous age and part of the Calaveras group. All of the deposits are lens shaped, and most have a northerly trend. They are interbedded with metasedimentary or metavolcanic rocks.

    "Most of the deposits utilized at present are high in calcium and low in magnesium, although one deposit is worked intermittently for magnesian limestone. Many are cut by dikes of fine- to medium-grained diorite, quartz diorite, and their schist equivalents. Also, some of the limestone deposits contain veins of chert. Jointing is prominent in much of the limestone.

    "The limestone deposits in the county are mined by open-pit and underground methods. In underground mining, shrinkage stopes are employed. At one time glory holes were employed by one producer. At various times one operator produces an entire year's supply with one blast. One producer delivers stone from the quarry to the lime plant via a 3-mile aerial tramway. Finished material from the plants is shipped by both truck and railroad."

    El Dorado County Slate

    "Slate has been mined in El Dorado County since about 1887. The Placerville area has been the largest and most consistent source of slate in California. At present most of the slate mined in California is from El Dorado County.

    "Nearly all of the slate mines in the county are between Placerville and Kelsey, where the Mariposa slate makes up a northwest-trending belt that averages 2 miles in width. Dip is vertical or steeply to the northeast. The slate is bluish-black in color when fresh and weathers to a brown or greenish-gray. Much of it is in uniform beds, with only a few small quartz veinlets or minor amounts of pyrite as impurities.

    "For many years, most of the slate mined in the county was dimension slate or squares, a unit equivalent of 100 square feet. The peak in slate production was reached in 1906 when 10,000 squares valued at $100,000 were produced. Dimension slate was used principally in shingles. Smaller amounts were used for blackboards, school slates, sinks, and as finished stone in homes. Major sources of dimension slate were the El Dorado Slate Products Company, which operated a quarry on the south side of Big Canyon 1 ½ miles north of Placerville, and the Eureka Slate Company, which owned a quarry 1 mile south of Kelsey. Slate from the Eureka quarry was delivered to Placerville via a 13,000-foot aerial cableway, which crossed the American River at an elevation of 600 feet above the bed of the river.

    "Because of the great amount of hand labor required and the resulting high costs, the production of dimension slate in El Dorado County gradually declined during the 1920's and finally ceased altogether. However, about this time the demand for crushed and ground slate for use as roofing granules and as filler material increased. In 1928, the old Chili Bar quarry was reopened by the Pacific Minerals Company. At present, this is the only active slate property in the county."

    El Dorado County Soapstone

    "For many years varying amounts of soapstone have been mined in El Dorado County. Soapstone is mined at the Swift property by the Pacific Minerals Company and intermittently at the Bernett and Hayden properties. It is marketed in the San Francisco Bay area for use as a carrier in insecticide dust.

    "Sawed slabs and blocks of soapstone were produced as early as the 1880's in El Dorado County (Logan, 1926, p. 450). These were used as building materials and for tubs, sinks, and stoves. Later substantial quantities of soapstone were mined for use as filler material for rubber, cloth, paint, paper, roofing and as a lubricant and in electrical insulation. Sources of soapstone during these times were the Swift mine near Latrobe, which operated from 1916-24, and the Rossi or Shingle Springs mine south of Shingle Springs, which was active from 1919-28. The Swift mine was reopened in 1928 by the Pacific Minerals Company and has been continuously active since.

    "Soapstone deposits in the Sierra Nevada are in or near talc-rich amphibolite schists or serpentine bodies in the western foothills. Most of the soapstone that has been mined in El Dorado County has been from the Latrobe-Shingle Springs area where there are extensive bodies of serpentine. The deposits range from small lenses a few inches thick to those hundreds of feet in extent. The soapstone is most commonly greenish-gray in color. Because of the iron oxide present in most Sierran soapstone, it has not been used in ceramics."

    El Dorado County Stone

    "Besides Dimension stone and slate, which have ben described in separate articles, El Dorado County is a source of sand and Gravel, crushed rock, riprap, and road Metal. Most of the output is used locally.."

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