Placer County

“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.)

Frontispiece. Aerial view of Cool-Cave Valley limestone deposits, camera facing south. Mountain Quarries of the Pacific Portland Cement Company in the foreground, quarry of the California Rock and Gravel Company in middle-ground. Cave Valley and adjacent gulches are roughly aligned parallel to the regional structure which is slightly north of west.

Geologic Map of the Cool-Cave Valley Area Showing Location of Limestone Deposits. (The limestone deposits mapped are: 1. Auburn, 2. Brown’s Bar, 3. Buckeye Canyon, 4. Burton, 5. Cool-Cave Valley, 6. Cowell, 7. DeWitt, 8. Hotaling, 9. Lime Rock, 10. West Cool-Cave Valley, 11. Long Point, 12. Muegge, 13. Pacific Portland Cement, 14. Rattlesnake Bridge , and 15. Spreckels.

Abstract

“The Cool-Cave Valley limestone deposit consists of two elongate lenses extending in northerly direction through the Sierran foothills about 4 miles east of Auburn, California. Limestone has been quarried from both lenses. Mountain Quarries, at the north end of the deposit, was one of the chief sources of limestone in northern California from 1910 to 1930. The California Rock and Gravel Company now (circa 1954) operates a quarry for the production of limestone for use in sugar refineries in the central portion of the deposit adjacent to the idle Mountain Quarries.

“The geologic structure of the area has a north to northwest trend. In the area immediately surrounding the limestone, the rock is composed dynamothermally metamorphosed fine-grained basic volcanic rocks commonly called greenstone, of undetermined age. To the west and north of the limestone are extensive beds of carboniferous metamorphosed marine sediments and masses of amphibolite. Both the limestone and the volcanic rocks are cut by dikes of medium-grained quartz diorite and diorite porphyry. The exact relationship of the limestone with the other rocks of the area is not clear.

“At Mountain Quarries, limestone was quarried by the glory hole method. From the quarry it was trammed through an adit to the crushing plant. Most of the stone was then shipped via railroad to the Pacific Portland Cement Company plant. After 1930 production was largely used in beet sugar refineries. Peak production varied from 1200 to 1500 tons per day.

“Since 1946, the California Rock and Gravel Company has operated a quarry in the central portion of the deposit. The ‘coyote hole’ method of quarrying is employed, whereby an entire year’s production of 150,000 tons is dislodged in one blast. The rock is then run through a crusher and a sizing plant. Coarser sizes are shipped via railroad to beet sugar refineries while the finer material is trucked to a lime plant near Rattlesnake Bridge or sold as road metal. Estimated reserves of the entire deposit are 18,225,000 tons per 100 feet of depth.

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

“Approximately 4 miles east of Auburn, California is the Cool-Cave Valley limestone deposit. The deposit consists of two elongate limestone lenses extending from a point half a mile north of the town of Cool, El Dorado County, north for a distance of approximately 1 ¾ miles to just north of the Middle Fork of the American River in Placer County. The two lenses lie in secs. 6 and 7, T. 12 N., R. 9 E., M.D.M. The bulk of the deposit is in El Dorado County .

“The Cool-Cave Valley area is traversed by State Highway 49 which crosses the south end of the deposit. Dirt roads branching off Highway 49 give access to nearly all parts of the limestone deposit. The nearest railroad is the main line of the Southern Pacific which runs through Auburn in a northeasterly direction. Until 1942, Mountain Quarries of the Pacific Portland Cement Company at the north end of the deposit on the Middle Fork of the American River, was served by a company-owned railroad which connected with the Southern Pacific at Auburn . The old railroad right-of-way is now a dirt road.

“Topography of the region is characterized by steep-walled canyons and moderately steep peaks. Elevations vary from 500 to 1800 feet. The topography and drainage pattern is partly controlled by the north to northwest trend of the major geologic structures. As the Sierra Nevada has been tilted in a general southwesterly direction, the main rivers and stream flow in that general direction, while the small tributaries tend to flow to the northwest or southeast in response to the structure.

Figure 1. Ruins of old lime kiln at the south Cool-Cave Valley deposit on the east side of State Highway 49.

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

“Limestone has been quarried at both of the lenses. Lime was produced in the early history of the operations by burning the lime with wood in stone lime kilns. During the 1880’s, the Cave Valley deposit was operated by the firm of Davis and Cowell (Hanks, 1884). In 1894 the Cave Valley Lime Company produced 150 to 160 tons of lime per month during the summer from two kilns which were located alongside of the Auburn-Cool road (Crawford, 1894). Ruins of these old kilns may be seen today north of Cool close to State Highway 49.

“In 1910 the Pacific Portland Cement Company opened its Mountain Quarries on the south side of the Middle Fork of the American River for the production of limestone for use in the company-owned cement plant in Solano County (Logan, 1947, p. 232). From 1910 until about 1930 this quarry was one of the chief sources of limestone for the cement, sugar, and steel industries in northern California. After 1930 production was smaller, the cement plant in Solano County having been idle part of the time. In 1942 the quarry was shut down, and the railroad and crushing plant were dismantled. Since that date, it has been idle.

“In 1946 the central portion of the northern lens, just south of Mountain Quarries, owned by the Henry Cowell Lime and Cement Company, 2 Market Street, San Francisco, was leased to the California Rock and Gravel Company, 1800 Hobart Building, San Francisco (Logan, 1947, p. 225). At the present time this firm operates a quarry at this site for the production of limestone, which is used chiefly in sugar refineries.

Figure 2. Old limestone quarry in the south Cool-Cave Valley deposit; view north from State Highway 49.

Figure 3. Mountain Quarries 1953; view south across the Middle Fork of the American River.

Figure 4. Mountain Quarries on the Middle Fork of the American River as seen from the Auburn-Forest Hill road in 1940 showing crushing plant and loaded train.

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

The general trend of the rock units is north to northwest. The rocks of the region consist of a series of dynamothermally metamorphosed marine sediments of the Calaveras group and metavolcanic rocks, some of which probably belong to the Calaveras group and some of which probably do not.

“The Calaveras group, of which the limestone has been considered as part, makes up the bulk of the Paleozoic part of the bedrock of the Sierra Nevada. For a long time the Calaveras group was considered to be Carboniferous in age; however, recent work has caused a number of investigators to believe that it includes a greater part of the Paleozoic section than just the Carboniferous (Taliaferro, 1943, p. 280). Stratigraphic relations of the limestone with other members of the Calaveras group are not clear in many areas.

Figure 7. Geologic map of the Cool-Cave Valley limestone.

Figure 8. North end of Mountain Quarries, camera facing north. To left a dikelike mass of amygdaloidal basalt crosses the limestone mass. To right, grooves in limestone give a fluted appearance.

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

“Metavolcanic Rocks. In the immediate area of the Cool-Cave Valley limestone, the enclosing rock consists chiefly of metamorphosed volcanic rocks, green schist and massive unlaminated greenstone being the most abundant. Moderately resistant as compared with the other rocks of the region, the greenstone occurs in bold massive outcrops. Massive blocky greenstone is most common east of the Cool-Cave Valley limestone whereas green schist is common to the west. Green schist is well exposed in road cuts in the vicinity of the State Highway 49 bridge over the Middle Fork of the American River.

“Where fresh, the massive greenstone is dull green to greenish-brown while the green schist is brilliant green. Both weather readily, first to a dull red or brown and then to a red soil.

“The greenstone and green schist have apparently derived from a series of fine-grained basic volcanic rocks, many of them tuffaceous. They are composed chiefly of chlorite with varying amounts of epidote, actinolite-tremolite, plagioclase, hornblende, zoisite, and small amounts of iron oxide and pyrite. Calcite is sometimes present in veinlets and cavities. Prophyroblastic textures are common.

“Amphibolite. Two miles west of the Cool-Cave Valley limestone is a 2000-foot-wide bed of hornblende-plagioclase amphibolite. It is massive to schistose and varies from a light-colored plagioclase-rich variety to a dark-green variety composed chiefly of hornblende.

“Cutting across the limestone in the north end of Mountain Quarries at a small angle to the elongation of the lens is a 45-foot wide dikelike mass of dark grayish-green rock containing numerous amygdules of white calcite. It is badly-sheared porphyritic amygdaloidal basalt composed of calcite amygdules and pseudomorphs of intermeshed calcite and relict plagioclase set in a dark fine-grained groundmass of chlorite and iron oxide.

“Diorite Porphyry. Both the limestone and the metavolcanic rocks in the vicinity of the limestone have been intruded by a number of diorite porphyry and quartz diorite porphyry dikes. They cut the limestone and metavolcanic rocks at small-angles both in dip and strike. The dikes are light to medium gray in color and are composed of phenocrysts of plagioclase, epidote, chlorite and iron oxide. Quartz may or may not be present. Much secondary calcite and usually small amounts of pyrite are present.

“Serpentine. Serpentine is widely distributed throughout the area. The largest serpentine body in this region crops out for about 1500 feet along an old railroad right-of-way on Robie Point in eastern Auburn. It is derived from basic intrusive rock, both the olivine and pyroxene have been altered to light and dark serpentine. There are many small serpentine bodies in the vicinity of the limestone, which have been altered to light iron oxide-stained talc.

“Metasedimentary Rocks. Metasedimentary rocks of the region include slate, chert, sheared sandstone and conglomerate, and limestone. All of the metasediments in the general area of the Cool-Cave Valley deposit have been considered to be part of the Calaveras group by Lindgren (1894). The Clipper Gap formation, part of the Calaveras group named by Lindgren, crops out in the southwestern portion of the adjoining Colfax quadrangle and is an extension of the series of metasediments in this area.

“Chert in this area varies from light to dark gray in color and is in places stained black with manganese oxide. The chert occurs in thin lenticular beds that are often contorted near the surface. Slate occurs in irregular beds and varies from a grayish cherty variety to a nearly black clayish variety. Also present in appreciable amounts are argillaceous sandstone, arkosic sandstone and fine- to coarse-grained conglomerate, all of which have undergone varying degrees of shearing.

“A wide belt of these metasediments are exposed along the Southern Pacific Railroad 3 miles to the north of the Cool-Cave Valley limestone deposit. A branch of this belt extends south to just east of the State Highway 49 bridge over the Middle Fork of the American River about one mile west of the limestone. Another wide belt of metasediments, which joins those to the north, extends in a general northwest direction about 2 miles east of the limestone.

Figure 5. Contact between limestone and a mass of amygdaloidal basalt that cuts across the limestone in the north end of Mountain Quarries.

Figure 6. Quartz diorite porphyry dikes cutting limestone in Mountain Quarries; camera facing north toward Auburn-Forest Hill road.

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 less 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.

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