Sibley Volcanic Regional Preserve

Round Top, one of the area’s highest peaks, is formed from lava and volcanic debris left behind by a 10-million-year-old volcano. Over millions of years, movement along the Hayward and Moraga earthquake faults uplifted the Berkeley hills, folding the underlying bedrock. In the northern half of the preserve, past quarrying opened up cross sections of the bedrock geology, creating an outdoor laboratory for studying volcanism in the Central Coast Ranges. Originally established as Round Top Park, the reserve remains one of the East Bay Regional Park District's founding properties.