Geology

The history of the Upper Quarry Amphitheater begins with the ancient bedrock that surrounds it. This rock began to form sometime between 1,700 million and 250 million years ago, when small grains of calcium carbonate—the skeletal remains of mollusks and corals—began to accumulate on the ocean floor where the Sierra Nevada mountains now stand. As this sediment was slowly buried beneath mud and sand, it ossified into the sedimentary rock known as limestone. About 130 million years ago, the extreme heat and pressure of underwater tectonic and volcanic activity caused the limestone to recrystallize into the metamorphic rock known as marble. Slowly, the movement of the plates carried this marble toward Santa Cruz. Then, as the Santa Cruz mountains formed, they lifted large areas of bedrock up and out of the ocean.

Marble bedrock, pictured in light blue on the map to the left, underlies much of the UC Santa Cruz campus. Outcrops, or places where the bedrock emerges from the ground, can be found along Jordan Gulch, the eastern and northern edge of McLaughlin Drive, and Porter Meadow. In some places, water has dissolved underground sections of marble, resulting in a landscape of sinkholes and caves. The hollow that forms the site of the Amphitheater, however, is man-made, created over the course of the 19th century as people extracted marble in order to turn it into quicklime.