Regional Geologic Structure (of El Dorado and Placer Counties)
“Structure sections accompanying the U. S. geological Survey folios that cover El Dorado and Placer County published during the period 1890-1900 indicate a regional homoclinal relationship of the stratified rocks of the basalt complex. Taliaferro (1943 pp. 285-286) in his studies along the Cosumnes River, which lies than 30 miles south of the Cool-Cave Valley limestone, has demonstrated that the relationships are far more complex and that the stratigraphy is complicated by large and small isoclinal folds and by major faults. Although detailed mapping on a regional scale was beyond the scope of this study, mapping of several strips across the regional trend of the formations indicated that similar structural conditions exist in the Cool-Cave Valley vicinity. Although slaty cleavage, schistosity and often major joint patterns tend to be parallel to the bedding in stratified rocks of the region, the relationship does not hold at crests and troughs of folds; cleavage and schistosity tend to be much more prominent than bedding. Interpretation of structure is further complicated by a lack of continuous distinctive beds and by a lack of time markers.
Cool-Cave Valley Limestone
“The large lenses comprising the Cool-Cave Valley deposit extend in a north direction for a distance of approximately 1 ¾ miles.
"The large northern lens, which is crossed by the Middle Fork of the American River at the northern end, is about 5500 feet long and averages 400 feet in width. Diamond drilling done by the Pacific Portland Cement Company showed this lens to extend to a depth of at least 800 feet below the original land surface of Mountain Quarries. (Tucker, 1916). the southern lens, which is crossed by State Highway 49, is 2000 feet long and nearly 600 feet wide in the middle.
“Being relatively resistant to erosion, the limestone stands out prominently from the surrounding metavolcanic rocks. The limestone is partially to completely recrystallized and is dense and tenacious. When fresh it is dark bluish gray to almost black in color. When weathered, it is light bluish gray. The limestone is generally even-grained, the individual crystals varying from 1 to 3 mm in diameter. A fetid odor of hydrogen sulfide is emitted when a fresh surface is hammered. Chemical weathering is most prominent along the joints. Small solution caves containing coarse crystalls (sic) of secondary aragonite are common along joints in the limestone.
“Although much of the limestone is completely recrystallized, a small mount of fossil debris is composed partly of coral and crinoid fragments of indeterminate age. Small amounts of pyrite are present in the limestone with the fossil debris.
“A considerable part of the Cool-Cave Valley limestone mass was originally composed of organic debris, much of it being of crinoid and coral fragments. Part of the mass may have been chemically precipitated. The original source of calcium carbonate may have been volcanic in part as suggested by the almost universal association of limestone with metavolcanic rocks in this area.
“At the north end of the Mountain Quarries some of the exposed surfaces of the limestone have a fluted appearance which is caused by a series of parallel grooves varying from one to several feet apart and one to several inches in depth. These grooves are parallel to the strike and were apparently formed on slip surfaces.
|Figure 9. Jointing in the limestone of Mountain Quarries.|
|Figure 10. Jointing in the limestone in the south Cool-Cave Valley deposit.|
Structure of the Limestone
"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 laces 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)
"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.|
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.
"Cool-Cave Valley (Coswell-Cave Valley) Deposit. Location: secs. 6, 7, and 18, T. 12 N., R. 9 E., M. D., 4 miles east of Auburn on the south side of the Middle Fork of the American River. Ownership: South 2/3, Henry Cowell Lime Cement Company, 2 Market Street, San Francisco; north 1/3, Ideal Cement Company, 310 Sansome Street, San Francisco.
|Figure 23. Limestone quarry of California Rock and Gravel Company. Camera facing north. (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.)|
|Fig. 39. The California Rock and Gravel Company limestone quarry on the south side of the Middle Fork of the American River east of Auburn. Photo by Olaf P. Jenkins. (From Geologic Guidebook Along Highway 49 - Sierran Gold Belt: The Mother Lode Country, Bulletin 141, Olaf P. Jenkins, Chief, California Division of Mines, San Francisco, California, 1949. Used with permission, California Department of Conservation, California Geological Survey.)|
"The largest limestone deposit in the county, the Cool-Cave Valley deposit has been a major source of limestone for the cement, lime, and beet-sugar industries for many years. It consists of two north-trending lenses. During the 1880's and 1890's, limestone was quarried from the south lens and burned in stone lime kilns (Clark, 1954, p. 441). Ruins of these old kilns are near State Highway 49. From 1910 to 1940, the Pacific Portland Cement Company operated an extensive quarry at the north end of the north lens by the Middle Fork of the American River. This deep quarry was known as Mountain Quarries. Limestone was sent through a crushing and sizing plant and shipped over a company-owned railroad to Auburn and then to the Pacific Portland Cement plant in Solano County or to beet sugar refineries. In 1942, the quarry was abandoned and the railroad dismantled.
"In 1946, the south portion of the north lens, south of Mountain Quarries, was leased by the California Rock and Gravel Company. This concern produces limestone for use in beet-sugar refining and lime manufacturing. A detailed study recently was made of this deposit, the results of which were published in the California Journal of Mines and Geology, vol. 50, July-October 1954, pp. 439-465.
"The deposit consists of high-calcium bluish-gray crystalline limestone. The north lens, which is cut by the Middle Fork of the American River near the north end, is about 5500 feet long and has an average width of 400 feet. It was worked to a depth of nearly 800 feet in Mountain Quarries. The south lens, which is crossed by State Highway 49, is 2,000 feet long and nearly 600 feet wide in the middle. A number of samples taken from both lenses averaged more than 97 per cent CaCO3 and less than 1 percent MgCO3 (Clark, 1954, p. 454). Country rock is green schist and massive greenstone. Both lenses are cut by dikes of medium-grained diorite and quartz diorite. The limestone is well jointed.
"At the California Rock and Gravel Company quarry in the south-central portion of the north lens, limestone is mined by several methods. In 1946 and 1947, it was quarried by benching with 30-foot wagon drill holes. From 1948 to 1952, it was mined with 'coyote' holes where adits were driven perpendicular to the quarry face and branches drive perpendicular to the adits. These were loaded with dynamite and an entire year's supply of limestone was dislodged with one blast (Clark, 1954, p. 458). At the present time large benches and 100-foot vertical wagon drill holes are used. About six months' supply is dislodged in one blast. Large fragments remaining from the blast are broken with a drop ball. In the fall of 1955, a new quarry north of the plant was being developed.
"Broken stone from the quarry is trucked to nearby crushing and screening plant. Coarse and medium sizes are trucked to Auburn and shipped by rail to beet-sugar refineries in the Sacramento and San Joaquin Valleys. The finer sizes are trucked to the Diamond Springs Lime Company for lime manufacturing. Until 1954, this concern also supplied limestone to the Vertin Lime Company plant at Rattlesnake Bridge. Undersize is stockpiled and sold as road metal. Twenty-seven men work at the quarry and plant.
Another limestone lens is located about one mile to the west on the Middle Fork of the American River. It also is composed of bluish-gray high-calcium limestone (Clark, 1954, p. 460). The lens, which strikes northwest, is 450 feet long and 50 feet wide. It was worked many years ago, and the stone was burned in a stone lime kiln at the north end."
“A mile and a half north of Cool, a group of limestone quarries can be seen on the north side of the highway. Limestone was first quarried and burned there some 40 or 50 years ago by the Cave Valley Lime Company. One of the kilns can be seen close to Highway 49 near the abandoned quarry, a quarter of a mile south of the road turnoff to the main workings. The kiln walls were made of limestone lined with greenstone. Local wood was used to fire the kilns. The present operators of the quarry, the California Rock and Gravel Company, quarry and crush the limestone for conversion into lump lime but do not produce either lime or cement themselves.”
Mine name: Cool Quarry; Operator: Spreckels Limestone & Aggregate; Address & County: P.O. Box 280, Cool, CA 95614, El Dorado County; Phone: (916) 885-4244; Latitude: 38.91, Longitude: -121.01, and Mine location number: Map No. 60; Mineral commodity: Limestone.
"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…."
The following information is taken from "Table 1. Limestone deposits in the general area of the Cool-Cave Valley limestone," (circa 1954) on pages 462 and 463:
(No. on map, Plate 3) 10; (Deposit) Limestone deposit one mile west of Cool-Cave Valley deposit near State Highway 49 bridge; (Owner) Pacific Portland Cement Company, 417 Montgomery Street, San Francisco; (Location) Sec. 12, T. 12 N., R. 8 E., M.D.