East Bay residents have several volcanoes in their backyard at Sibley Volcanic Regional Preserve, which shares with Temescal and Tilden the distinction of being one of the District’s original parks. Round Top, a peak within Sibley and one of the highest peaks in the Oakland hills, is made up of lava and volcanic debris left over from a 10-million-year-old volcano. Though Round Top was once the infilling of a great cauldron, it stands out today because it was originally surrounded by sedimentary rocks of the Orinda Formation, which have eroded away. During the past 10 million years the Berkeley Hills were uplifted on a gigantic scale because of strains on the Hayward and Moraga fault systems. This uplift entailed folding of the rock formations, and the Round Top complex was tilted on its side. Operated by the East Bay Regional Park District.