Alum Rock Park lies in a narrow valley of the Diablo Range foothills along Penitencia Creek. The land has been public since the pueblo’s founding, and it became a city park in 1872. It was first known simply as “the reservation” and took its present name around 1900, from rocks near the entrance that were mistaken for alum. Its 13 miles of trails climb from the creek to the North and South Rim trails, with views over the Santa Clara Valley, and the valley floor has mineral springs, picnic lawns and a visitor center.
From the 1890s a railway carried visitors from downtown San Jose up into the park, first with steam dummies and later electric cars, until service ended in 1932. By the 1960s crowds had worn the park down, and in the 1970s most of its buildings were removed to let the canyon return to a more natural state.