Robert Sibley Volcanic Regional Preserve is located in the San Francisco Bay Area, California, East Bay region’s Berkeley Hills. The park is part of the Eastern Bay Regional Parks District (EBRPD), covering 928 acres (3.76 km2), and lies east of Oakland, partly in Alameda County and partly in Contra Costa County. It can be accessed via Skyline Boulevard from Oakland, or from Contra Costa County via Old Tunnel Route.


The park was one of the first three parks the East Bay Regional Parks District (EBRPD) founded in 1936. Originally it was called Round Top Regional Park. The Round Top (1.761 feet high [537 m]) is an extinct volcano in the Berkeley Hills. It has at least two labyrinths of stone of recent origin in it. The park was renamed shortly after his death, after the EBRPD ‘s second president, Robert Sibley.


The preserve contains a volcanic core of the Pliocene epoch that, some ten million years ago, formed most of the lavas that underlie the ridges of the East Bay from Inspiration Point in Tilden Regional Park to Moraga. Geologists refer to the local volcanism as the Volcanics of Moraga. The lava-bearing rock formations were folded by subsequent compressive strains created by various local defects such as the Hayward Fault, tilting the Round Top vent complex to its side.

Folding, erosion, and a quarry operation exposed a cross-section of the volcano, providing an excellent way of studying a volcano in the California Coast Ranges. UC Berkeley ages lava inside the vent at the age of 9.5 million years.


The preserve includes many walks. Most are limited to hiking and horseback use and there is only a handful suitable for multi-purpose use. Round Top Path is paved to the top of the Round Top from the visitor center. The preserve is without campgrounds or picnic areas. The visitor center at the entrance to Skyline Boulevard is unstaffed and has brochures for self-guided tours available. It also includes depictions of the geology of the area.

Hiking trails

  • The 31 miles (50 km) long East Bay Skyline Regional Trail traverses the Sibley preserve on the ridgeline separating Wildcat Canyon Regional Park and Anthony Chabot Regional Park.
  • Round Top Road goes from the Sibley visitor center to the peak of Round Top.
  • Round Top Loop Trail circles Round Top’s peak.
  • Volcanic Trail, once a quarry haul road, contains most of the stops on the self-guided volcanic tour.
  • Quarry Trail connects the middle of Volcanic Trail to a point lower down on Quarry Road.
  • Pond Trail is a short trail segment that descends to a couple of ponds on the north side of the preserve.
Image courtesy of Jeffreymendel Jeffrey Nash – Own work, CC BY 3.0,

This interesting site is located near the following must-see sights in Lafayette, California:

  • Lafayette BART Station
  • Cross of Lafayette Memorial
  • Lafayette Park Theater
  • La Fiesta Shopping Center
  • Lafayette Reservoir
  • Grizzly Peak
  • Lafayette Community Park
  • The Clocktower Lafayette

All of these landmarks are located just a short distance from our location in downtown Walnut Creek, Spaulding Concrete on Locust Street!