This park has some of the best views in San Francisco, but don’t overlook the wonderful wildflower display that carpets the grasslands each spring. Among the flowers you may see here are checkerbloom, California poppy, footsteps of spring, Douglas iris, mule’s ears, and Johnny jump-up, a sensitive species that is the only host plant for the callippe silverspot butterfly. Also look for anise swallowtail, a big yellow butterfly with black shoulders that frequents San Francisco’s hilltops. A network of dirt trails wind around the hill and lead to the summit.
Corona Heights’ prominent red rock outcrop, visible from many parts of the city, began to develop about 200 million years ago in the middle of the Pacific Ocean. Magma emerging through the earth’s crust at the spreading center between the Pacific and Farallon plates contacted sea water and cooled to form pillow basalt, the bedrock of oceans everywhere. Over the next 75 million years, radiolaria—amoebae-like unicellular organisms with silica-rich exoskeletons—lived, died, and drifted down through the deep waters to the ocean floor. Eventually the combination of pressure and time turned these microscopic organisms into the rock we call radiolarian chert.
The movements of the tectonic plates brought the Corona Heights rock close to the North American continental shore tens of millions of years ago. Sand eroding from the Sierra Nevada washed into the ocean and turned to sandstone layered atop the chert. As the Farallon plate subducted under the Continental plate, the rocks of Corona Heights were scraped off, scrambled up, and pitched onto the land, forming the park’s current landscape.
On the northeast slope, at the base of the hill, is an excellent example of “slickensides,” a smooth, polished surface between two masses of rock that is created by tectonic sliding. Usually slickensides are found in softer rock; this example in chert is highly unusual. This slick vertical rock face can best be seen from Beaver and 15th streets.
In the late 1800s, Corona Heights was quarried for brickmaking materials. The infamous Gray brothers had a brick kiln on States Street, where remnants of the brickyard buildings can still be seen. The kiln burned during the 1906 earthquake, causing some people to think a volcano had erupted on Corona Heights. After repairs, quarrying continued.
The Gray brothers were seen as “constant law breakers,” and were accused of injuring neighbors and damaging property with debris from illegal rock blasting here and in other quarries in San Francisco. In 1914, George Gray was murdered by a former employee who was owed back wages. An unsympathetic jury acquitted the defendant.
All the steep, exposed rock faces and the “crown” we see today at Corona Heights are the result of quarrying, as are some early names used for this hill: Rocky Mountain, Red Rock, and Rocky Hill. Today, tennis courts, playing fields, and the Randall Museum all occupy large quarried areas.
A natural history museum for children, the Randall Museum was the inspiration of Josephine D. Randall, San Francisco’s first superintendent of recreation. “Rocky Hill” was purchased by the city in 1940 and renamed Corona Heights. In 1947, Ms. Randall shepherded a $12 million bond issue for recreation capital projects, including a new junior museum building, which opened in 1951 on Corona Heights.
Corona Heights has a lot of poison oak, which provides food for dark-eyed juncos and white-crowned sparrows, and shelter from predators and habitat for many of the insects that birds feed on. However, poison oak can give humans an itchy rash. Learn to recognize this plant by its three shiny green (sometimes red) leaves and tan spine-free stems. Poison oak oils can be transmitted to humans via dog hair, so be sure to keep your dog on leash and on trail.