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Home > ]California > CA - Quarry Links & Photographs > El Dorado County > List of Quarries > Mountain Quarries (Continued)
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 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 |  |
"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 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. |  |
| 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. |  |
| Figure 9. Jointing in the limestone of Mountain Quarries. |  |
| Figure 13. Mountain Quarries, camera facing south. The quarry walls are nearly 600 feet high. |  |
| Figure 14. California Rock and Gravel Company quarry; camera facing north. Fall, 1952. |  |
| Figure 15. California Rock and Gravel Company quarry in Spring, 1953. |  |
| Figure 16. 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. |  |
| Figure 18. 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. |  |
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.
A railroad line was constructed by the Pacific Portland Cement Company in the early 1900s to connect their limestone operation to the main line of the westbound Southern Pacific in Auburn, California. It was called the "Mountain Quarry."
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