Permanente Quarry

The Permanente Quarry and cement plant is in an unincorporated area of Santa Clara County, California, just west of Cupertino. The limestone and aggregate mining operation and cement plant is owned by Lehigh Southwest Cement, a subsidiary of Heidelberg Cement. Limestone was mined beginning in 1902 but remained a small operation until 1939 when it was purchased by Henry J. Kaiser to supply the 5.5 million barrels of cement to build Shasta Dam. With increased production Kaiser supplied all of the cement used by the Navy in the Pacific Theater of World War II. At 7 million barrels, it was more cement than the Shasta Dam project. Roughly 70 percent of the cement used in the communities of Santa Clara County was acquired from the cement plant. Located in the foothills above Cupertino on the northeast slopes of Black Mountain, the quarry runs east–west parallel to the upper watershed of Permanente Creek to the south and to Permanente Ridge and Rancho San Antonio Open Space Preserve to the north. The limestone rock found in the Permanente Creek valley and on the summit of Black Mountain is relatively unique in the Bay Area. Microfossils in the limestone deposits suggest that the mountain originated as a seamount at 22 degrees north in the tropical Pacific about 100 million years ago and was transported to Los Altos by the Pacific Plate. These rocks occur as jagged gray boulders and outcrops just southwest of the radio towers on the summit of Black Mountain, as well as in the Permanente Quarry.