East Bay residents have a volcano in their backyard at Sibley Volcanic Regional Preserve. Originally called Round Top Park, Sibley shares with Temescal and Tilden the distinction of being one of the East Bay Regional Park District's original parks. The preserve was later named in honor of Robert Sibley, who helped found the District and served for 10 years on its board of directors.
To Reach The Park
Round Top Road is paved to the top of Round Top. (Watch for occasional vehicles using the road.) There is also a 600-foot, paved wheelchair path north of the visitor center that ends at a viewing platform. Quarry Road, beginning at Old Tunnel Road, is also paved.
Round Top (elevation 1763 ft. above sea level) is the preserve's most prominent feature.
The unstaffed visitor center at the Skyline Boulevard staging area has displays illustrating the preserve's geology. A self-guided brochure is available at the staging area highlighting the preserve's geological features.
Several trails provide access throughout the preserve. The 31-mile East Bay Skyline National Recreation Trail, part of the Bay Area Ridge Trail system, traverses the preserve along the ridgeline between Wildcat Canyon and Anthony Chabot Parks. Round Top Road goes from the Sibley visitor center to the top of Round Top. Round Top Loop Trail circles Round Top peak. Volcanic Trail, once a quarry haul road, contains most of the stops on the self-guided volcanic tour.
From Old Tunnel Road on the northwest side of the park, the paved Quarry Road ascends and meets the east end of Volcanic Trail. Quarry Trail connects the middle of Volcanic Trail to a point lower down on Quarry Road. Finally, Pond Trail is a short trail segment that descends to a couple of ponds on the north side of the preserve.
Most trails are hiking and equestrian only. A few trails are multi-use. Dogs are permitted at Sibley, but are not allowed on adjacent Huckleberry trails. A visitor center at the park shelves self-guided tour brochures so guests can stroll the park and learn of its historic significance at their own leisure.
Bicycles are not allowed on narrow-gauge trails, except on the Skyline Trail between the Sibley visitor center and Old Tunnel Road. Bicycles are allowed on the wider-gauge fire trails and paved roads, but are not allowed on Round Top Road from the fork .15 mile east of the visitor center to the top of Round Top.
Round Top, one of the area's highest peaks, is made up of lava and volcanic debris left over from a 10-million-year-old volcano. During the past 10 million years, massive tectonic forces on the Hayward and Moraga earthquake faults uplifted the Berkeley hills, folding bedrock formations and tilting the Round Top volcano complex on its side.
Softer sedimentary rock from the Orinda Formation eroded away, exposing the Round Top volcano. In addition, quarrying in the north half of the preserve has revealed cross sections of the bedrock geology, providing an unsurpassed outdoor laboratory for studying volcanism in the Central Coast Ranges.