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  • The Cool-Cave Valley Limestone Deposits, El Dorado and Placer Counties, California,” by William B. Clark, Junior Mining Geologist, California Journal of Mines and Geology, Vol. 50, Nos. 3 and 4, July-October 1954, California State Mining Bureau, pp. 439-466. (Used with permission, California Department of Conservation, California Geological Survey.)

    Structure of the Limestone (of the Cool-Cave Valley Limestone Deposits, El Dorado and Placer Counties, California)

    “Strike of bedding and schistosity in the northern lens varies from north to N. 15 ° W. Dip is both to the east and west and ranges from 75 degrees to vertical. Parallel jointing is prominent. The joint planes of the principal series of joints are 1 to 15 feet apart and have a strike nearly perpendicular to that of the bedding. Dip of the joints is north and ranges from 20 to 35 degrees. Secondary joints if present, are either parallel to the strike of the bedding or are perpendicular to the bedding and dip south.

    “Bedding and schistosity of the southern lens strike approximately N. 15 ° E. and dip 75 to 85 degrees northwest. As in the northern lens, joints are nearly perpendicular to the strike of the bedding and schistosity and dip 20 to 35 degrees northeast.

    “No definite conclusion can be reached in regard to the precise position of the limestone lenses in the stratigraphic sequence or to the exact structural relationship between the limestone and the enclosing rocks. However, several interpretations are possible based on the following observations:

    “1. In some places differential movement between the limestone and the enclosing greenstone is plainly indicated; in others there is no evidence of differential movement. In places where there have been differential movements their magnitude cannot be measured. In and adjacent to the glory hole at Mountain Quarries, a quartz diorite dike cuts diagonally across the limestone-greenstone contact. It has not been displaced at the contact showing that any movement which might have taken place along the contact would have occurred prior to the emplacement of granitic rocks in Upper Jurassic time.

    “2. The Cool-Cave Valley deposits are bordered entirely by greenstone as are several smaller lenses exposed along the Forest Hill road and elsewhere in the area. Other limestone lenses in the general area are bordered entirely or partly by other metasediments such as slate, mica schist, meta chert, etc.

    “3. The Cool-Cave Valley limestone bodies occupy a median position between two belts of metasediments. One and a half miles northwest of the deposits along the canyon of the North Fork of the American River, metasediments of the Clipper Gap formation are interfolded with greenstone. The area distribution of the wedge-shaped salients, as seen on the accompanying map, strongly suggests a succession of steeply pitching, large-scale isoclinal folds. This relationship is well seen on a smaller scale in roadcuts along the south side of the North Fork Dam road in the extreme northwest corner of sec. 1, T. 12 N., R. 8 E., M.D.B. and M. There, metavolcanics are stratigraphically below metasediments in the crest of an anticline.

    “4. At the north end of Mountain Quarries the limestone is crossed by a tabular mass of sheared, altered, amygdaloidal, basic volcanic rock similar in character to some facies of the enclosing greenstone. The amygdaloidal mass transgresses slightly the regional trend of the limestone lens south of the American river and north of the river a similarly trending mass is found a few feet within the enclosing greenstone. The amygdaloid has obviously been deformed with the limestone prior to emplacement of the dioritic dikes.

    “Three possible structural interpretations are:

    “1. If the displacement along the contact between the limestone and greenstone is interpreted as having been of great magnitude, then the limestone could have reached its present position by major faulting, plastic flow or a combination of both prior to Upper Jurassic time.

    “2. If displacement along the contact and presence of isoclinal folding are discounted as being of minor importance only and the stratigraphic sequence is interpreted as homoclinal as shown on the folios, then the limestone could be interpreted simply as a lenticular member interbedded with the enclosing greenstone.

    “3. The relative position of the limestone lenses with respect to the position of the greenstone and the Calaveras group metasediments suggests a major structure with the limestone lenses lying roughly along the axis of that structure. However, since the relative ages of the greenstone, Calaveras group, and limestone are uncertain, judgment of such a structure as anticlinal or synclinal is not possible.

    Analyses of the Limestone (in Cool-Cave Valley, El Dorado and Placer Counties, California)

    “Nearly all of the limestone in the Cool-Cave Valley deposit is high in calcium carbonate and low in magnesium carbonate. A total of 45 samples were taken from both lenses. Samples of fresh limestone, varying from 2 to 4 pounds in weight, were taken at regular intervals across the strike of the lenses and several composite samples of small chips were taken along the margins of the southern lens.

    “All but one of the eleven samples taken from the north portion of the north lens north of the Middle Fork of the American River contained more than 98 percent calcium carbonate. Three of the eleven samples contained slightly more than 1 percent while the other eight contained less than 1 percent magnesium carbonate.

    “Many samples were taken in Mountain Quarries, both from along the margins of the lens and from near where the limestone is cut by diorite porphyry dikes and amygdaloidal basalt. Other than two samples taken next to the limestone-amygdaloidal basalt contact, which ran slightly over 90 percent calcium carbonate and about 5.5 percent insoluble material, all others varied from about 96.4 to 98.6 percent calcium carbonate, .5 to 1.6 percent magnesium carbonate and 1 percent or less insoluble. Five samples taken from the strike at the southern end of the north lens averaged 97.6 percent calcium carbonate and 1.1 percent magnesium carbonate.

    “The following are analyses supplied by the California Rock and Gravel Company of four limestone samples from lots shipped from their quarry in the central portion of the north lens.

    “Five samples taken across the north end of the south lens averaged 96.8 percent calcium carbonate and 0.77 percent magnesium carbonate. Sample number 10, a composite sample taken along the northwest margin of the lens which contained 93.8 percent calcium carbonate and 4.6 percent insoluble material, is not believed to be truly representative of the deposit as the limestone is deeply weathered in this part of the deposit. Four samples taken from the southern end of the south Cool-Cave Valley deposit averaged 97.1 percent calcium carbonate and 1.2 percent magnesium carbonate.

    “In general, the deposit is nearly uniform in composition. There are no noticeable changes in composition across the strike of the lenses. Apparently, there has been very little contamination from outside sources. Except in a few places at the extreme outer edge of the lenses and where the limestone has been deeply weathered, composition of the deposit is 97 to 99 percent calcium carbonate.

    Figure 11. North end of the Cool-Cave Valley deposit on the north side of the Middle Fork of the American River; camera facing north. North end of the Cool-Cave Valley deposit on the north side of the Middle Fork of the American River

    Quarrying and Milling Operations (at Mountain Quarries Cool-Cave Valley Limestone Deposit)

    “Limestone at Mountain Quarries was quarried by the glory hole method. Three glory holes were connected by raises from an 1800-foot south-extending adit. The adit entered the hillside at a point about 70 feet above the river. The glory holes have vertical sides and have been worked to a depth of about 600 feet. Limestone was quarried to within a few feet of the edge of the lens. This practice prevented the walls from caving as the limestone is much more rigid and tenacious than the surrounding volcanic rocks. The parallel joints in the limestone were an aid in quarrying operations.

    “Overburden was removed by steam shovels. Stone was then blasted from the quarry faces, dumped down the raises to chutes and then to 6-ton cars in the adit. The cars were then trammed out the adit to the crushing and sizing plant. Before crushing, it was hand-sorted to remove the dike rock and other foreign material. The stone was then fed to a gyratory rock crusher and then to trommels where it was washed and sorted. It was conveyed to railroad cars and shipped over a seven-mile company-owned railroad to Auburn .

    “Three sizes; 2 ½-inch, plus 2 ½-inch minus 4-inch, and plus 4, minus 8-inch were produced. The 2 ½-inch rock was shipped to the Pacific Portland Cement Company cement plant in Solano County while the coarser sizes were shipped to sugar refineries (Young, 1925). Peak production varied from 1200 to 1500 tons of limestone per day. About 140 men were employed at the quarry and plant.

    Figure 13. Mountain Quarries, camera facing south. The quarry walls are nearly 600 feet high. Mountain Quarries, camera facing south

    “In 1946, the central portion of the northern lens south of Mountain Quarries, owned by the Henry Cowell Lime Company, 2 Market Street, San Francisco, was leased by the California Rock and Gravel Company, 1800 Hobart Building, San Francisco. For a time this property was worked for them under contract by E. B. Bishop. Production during this period was several hundred tons per day (Logan, 1947, p. 225). Since 1947, the California Rock and Gravel Company has operated the quarry. Since 1948, the ‘coyote hole’ method of quarrying has been employed. A quarry face 65 feet high and more than 300 feet long is being worked. Near the base of the quarry 40-foot adits or ‘coyote holes’ 80 to 100 feet apart are driven perpendicular to the quarry face. At the ends of the adits 30-foot branches are driven perpendicularly or at large angles from the line of the adit so that they end about 20 feet from the end of the adjacent branch. The adits and branches are then loaded with 40 percent Atlas dynamite. In 1952 approximately 18 tons of dynamite were used for this operation.

    “The entire dynamite charge is then shot electrically. About 150,000 tons are dislodged in the single blast, enough to sustain continuous plant operation for an entire year.* Secondary breaking of stone in the quarry is done with a 4-ton steel drop ball suspended from a crane. Power shovels then load the limestone into dump trucks which deliver it to the crushing plant about 1000 feet north of the quarry.

    (* Page 458 footnote: Kelly, George, personal communication, 1952.)

    “At the crushing plant the limestone is delivered to an electrically operated 30- by 42-inch primary jaw crusher, set at 7 ½ inches. The rock then passes by belt conveyor to a trommel with 6-inch square holes. Oversize goes to a secondary crusher while undersize is delivered by inclined belt conveyor to a three-deck inclined trommel on top of three loading bins. Three sizes: plus 4- by minus 6-inches, plus 2- by minus 4-inches, and plus ½-minus 2-inches are classified into the bins. The minus ½-inch rock is delivered by belt conveyor to a stockpile east of the crushing plant.

    “The coarsest and middle sized stone in the bins is trucked to Auburn where it is loaded into railroad cars and shipped to beet sugar refineries in the Sacramento and San Joaquin Valleys. The finest binned stone is trucked to the Hughes Vertin Lime Company plant at Rattlesnake Bridge where lime is manufactured in inclined rotary kilns. Occasionally, some of the plus ½- by minus 2-inch limestone is shipped to steel plants in the San Francisco Bay area where it is used as a flux in open-hearth steel furnaces. Nearly all of the undersize rock, not binned, is sold as road metal.

    Figure 14. California Rock and Gravel Company quarry; camera facing north. Fall, 1952. California Rock and Gravel Company quarry
    Figure 15. California Rock and Gravel Company quarry in Spring, 1953. California Rock and Gravel Company quarry in Spring
    Figure 16. East face of California Rock and Gravel Company Quarry near the main entrance. East face of California Rock and Gravel Company Quarry near the main entrance
    Figure 17. California Rock and Gravel Company plant. Quarry is out of view to right. California Rock and Gravel Company plant. Quarry is out of view to right
    Figure 18. Sizing plant and loading bins at the California Rock and Gravel Company plant. Sizing plant and loading bins at the California Rock and Gravel Company plant
    Figure 19. Crushing plant and trommel at the California Rock and Gravel Company plant. Crushing plant and trommel at the California Rock and Gravel Company plant

    Estimated Reserves (of Mountain Quarries)

     “It is estimated that the northern portion of the north lens, north of the Middle Fork of the American River, contains 1,125,000 tons of limestone per 100 feet of depth. The northern lens south of the river is estimated to contain 11,250,000 tons of limestone per 100 feet of depth. This estimate excludes that portion of limestone which has already been removed from Mountain Quarries. The southern lens is estimated to contain 5,850,000 tons of limestone per 100 feet of depth. Estimated tonnages are based on the limestone having an approximate weight of 150 pounds per cubic foot.

     Other Limestone Deposits in the Area (of Mountain Quarries)

    “A number of other limestone deposits are in the general area of the Cool-Cave Valley deposit. The majority lie to the north and to the east in Placer County while a few are to the south in El Dorado County. Nearly all of the deposits have been worked at one time or another. Ruins of old stone lime kilns are at nearly every limestone deposit in the region.

    “Like the Cool-Cave Valley deposits, these deposits consist of almost completely recrystallized high-calcium limestone. On the basis of a small amount of fossil evidence, all are considered to be Carboniferous in age and to be part of the Calaveras group.

    “Approximately one mile west of the Cool-Cave Valley deposit on the south side of the Middle Fork of the American River, about 2000 feet southeast of the State Highway 49 bridge, is a small northwest-trending lens of dark bluish-gray limestone enclosed in metasediments. It is about 450 feet long and 50 feet wide….”

    “A deposit known as the Auburn deposit just east of Auburn was quarried many years ago. It is composed of somewhat shattered white marble (Aubury, 1906, p. 101).

    “Just north of Auburn in sec. 3, T 12 N., R. 8 E., M.D.M., is the Burton deposit which is composed of light gray, fine-to-medium-grained limestone….”

    “The Cowell deposit 4 miles north of Auburn is partly covered by soil. The limestone is dark gray in color….”

    “Approximately 9 miles to the southwest is the Rattlesnake Bridge (Alabaster Cave) deposit. It is a north-striking high-calcium limestone deposit containing rock that is white to gray in color. It has an even, granular texture….”

    “Limestone has been produced from this deposit since the 1860’s. Between 1930 and 1942 the deposit was worked by the Auburn Chemical Lime Company. In 1946, a rotary kiln and crushing equipment were installed. During that year the lime plant utilized limestone quarried at this deposit. Since 1947, however, all limestone has been purchased from the California Rock and Gravel Company at the Cool-Cave Valley deposit. Most of the lime produced is shipped to steel plants (Logan, 1947, p. 224).

    North of the Cool-Cave Valley deposit in sec. 30, T. 13 N., R. 9 E., M.D.M.,...south of Clipper Gap station are two smaller deposits, Lime Rock and the DeWitt deposit.

    “Lime Rock, a well-known landmark of the area, stands out prominently from the surrounding metavolcanics and metasediments. On the north end, the deposit rises 70 feet above the land surface, while at the south end the face extends at least 500 feet down the slope toward the North Fork Dam. The deposit is about 150 feet wide and 300 feet long….”

    “The DeWitt deposit is about half a mile northwest of Lime Rock just north of Clipper Creek. It is 250 feet long and varies from 50 to 100 feet in width. Six samples taken from this deposit were analyzed by Abbot A. Hanks, Inc….”

    “Southeast of Lime Rock on the south side of North Fork reservoir is the Muegge deposit which is partly covered by water. Although it is 225 feet wide at the water’s edge, it extends for only a short distance up the slope.”

    “At Hotaling, 3 ½ miles west of Clipper Gap is a small deposit of coarse, white, granular limestone. This was used at the iron smelter operated at Hotaling in the 1880’s (Logan, 1947, p. 264)….”

    “The Spreckels deposit half a mile southeast of Applegate was worked by the Spreckels Sugar Company for one year ending in October 1916. It is fine-grained bluish-gray limestone. The deposit is 650 feet long and varies from 100 to 200 feet in width (Logan, 1927, p. 282).

    “Lying to the east on both the Middle and North Forks of the American River are several other limestone deposits. The largest of these, which is listed in the tabulated list as the Pacific Portland Cement deposit, is cut by the North Fork of the American River and is 2 ½ miles south of Applegate. It is nearly a mile long and several hundred feet wide. The limestone is medium-grained and light-blue-gray in color. Veins and veinlets of chert are present here and there in this deposit.

    “Just east of this on Long Point is a small deposit of cherty limestone.

    “Two other deposits are at Brown’s Bar and Buckeye Canyon on the south side of the Middle Fork of the American River about 3 miles east of the Cool-Cave Valley Deposit. Both deposits, owned by the Pacific Portland Cement Company, 417 Montgomery Street, San Francisco, apparently have never been worked because of their inaccessability (sic).”

    Bibliography (for the Cool-Cave Valley Limestone)

    Aubury, Lewis E., 1902, El Dorado County: California Min. Bur. Register of Mines and Minerals, p. 17.
    Aubury, Lewis, E., 1906, The structural and industrial materials of California: California Min. Bur. Bull. 38.
    Bowen, O. E., Jr., and Crippen, R. A., Jr., 1948, Geologic maps and notes along Highway 49: California Div. Mines Bull. 141, p. 70, 73, 80.
    Crawford, J. J., 1894, California Min. Bur. Rept. 12, p. 391-392.
    Crawford, J. J., 1896, California Min. Bur. Rept. 13, p. 628.
    Hamilton, Fletcher, 1919, California Min. Bur. Rept. 15, p. 304.
    Hanks, Henry G., 1884, California Min. Bur. Rept. 4, p. 107.
    Jerkins, Olaf P., 1938, Geologic map of California, scale 1:500,000: California Div. Mines.
    Knopf, Adolph, 1929, The Mother Lode system of California: U. S. Geol. Survey Prof. Paper 157, p. VII.
    Laizure, C. McK, 1927, California Min. Bur. Rept. 23, p. 208.
    Laizure, C. McK., 1929, California Min. Bur. Rept. 25, p. 251.
    Lindgren, Waldemar, 1894, U. S. Geol. Survey Atlas, Sacramento folio (no. 5), 12 pp., 4 maps.
    Lindgren, W. and Turner, H. W., 1894, U. S. Geol. Survey Atlas, Placerville folio (no. 3), 9 pp., 4 maps.
    Logan, C. A., 1921, California Min. Bur. Rept. 17, p. 432.
    Logan, C. A., 1924, California Min. Rept. 20, p. 8.
    Logan, C. A., 1926, California Min. Bur. Rept. 22, pp. 442-443.
    Logan, C. A., 1927, California Min. Bur. Rept. 23, pp. 281-282.
    Logan, C. A., 1938, California Div. Mines Rept. 34, pp. 277, 280.
    Logan, C. A., 1947, Limestone in California: California Div. Mines Rept. 43, pp. 224-226, 231-233.
    Taliaferro, N. L., 1943, The Calaveras: California Div. Mines Bull. 125, pp. 280-282.
    Tucker, W. B., 1919, Mountain Quarries: California Min. Bur. Rept. 15, p. 304.
    Young, George J., 1925, Quarrying limestone by glory holes: Eng. and Min. Jour.-Press, Vol. 120, pp. 13-16.

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