Permanente Quarry, Limestone quarry in Santa Clara County, California

Permanente Quarry is an active limestone and aggregate mining operation and cement plant on the northeast slopes of Black Mountain in Santa Clara County, California, just west of Cupertino. The limestone occurs as jagged gray boulders and outcrops; microfossils in the deposits indicate the rock originated as a seamount at 22 degrees north in the tropical Pacific about 100 million years ago and was carried to Los Altos by the Pacific Plate.

Mining started here in 1902 as a small operation, and Henry Kaiser bought the site in 1939 to supply cement for the construction of Shasta Dam. After that purchase, it grew into one of the largest cement producers in the region.

The name comes from Permanente Creek, whose valley holds the quarry; Henry J. Kaiser's 1939 cement plant was first called Kaiser Permanente Cement. The plant supplied roughly 70 percent of the cement used in Santa Clara County communities, and its output went into Shasta Dam and Navy construction in the Pacific during World War II.

The site is an active industrial operation, so public access is very limited and the area is not set up for casual visits. There are plans to turn parts of the land into open space and housing, which could change what is accessible in the coming years.

During World War II, this facility supplied all the cement used by the Navy across the Pacific and had around 2,000 workers on site. The demand was so high that operations ran without stopping.