Robert Sibley Volcanic Regional Preserve
Robert Sibley Volcanic Regional Preserve is located in the Oakland Hills of the East Bay region of the San Francisco Bay Area, California. The park is part of the East Bay Regional Parks District (EBRPD), covers , and lies east of Oakland, partly in Alameda County and partly in Contra Costa County. It can be entered from Oakland via Skyline Boulevard, or from Contra Costa County via Old Tunnel Road. History. The park was one of the first three parks established by the East Bay Regional Parks District (EBRPD) in 1936. It was originally named Round  Top Regional Park. Round Top (elevation ) is an extinct volcano in the Oakland Hills which started to erupt 10.2 Million years ago. It is home to at least two stone labyrinths of recent origin. The park was renamed after the second president of the EBRPD, Robert Sibley, shortly after his death. Geology. The preserve contains a Pliocene epoch volcanic center that, about ten million years ago, produced most of the lavas that underlie the East Bay ridges from Inspiration Point in Tilden Regional Park to Moraga. Geologists refer to this local volcanism as the Moraga Volcanics. Subsequent compressive strains produced  by various local faults such as the Hayward Fault folded the lava-bearing rock formations, tilting the Round Top vent complex on its side. Folding, erosion, and a quarry operation exposed a cross section of the volcano, providing an excellent means to study a California Coast Ranges volcano. Lava within the vent has been dated by UC Berkeley at 9.5 million years old. Activities. There are several trails in the preserve. Most are restricted to hiking and horseback use and only a few are available for multi-purpose use. Round Top Road is paved from the visitor center to the  top of Round Top. There one campgrounds or but no picnic areas in the preserve; there are plenty of benches good for a rest, view and snack. The visitor center at the Skyline Boulevard entrance is unstaffed and offers brochures for self-guided tours. It also features depictions of the region's geology. Labyrinths. At least two man-made labyrinths exist within RSVRP. The first, and arguably most frequently visited, is known as the Mazzariello Labyrinth. Constructed in 1990 and donated as a "gift to the world" by East Bay resident Helena Mazzariello, it is a favorite destination for hikers  who come to pray, meditate, and examine talismans left in the center by previous visitors. Notwithstanding the official gate hours listed below, Friends of the Labyrinth claims that the labyrinth has visitors 24 hours a day, 7 days a week. The next marker along the Round Top Loop Trail leads to the Volcanic Trail, which crosses to the left. At Post No. 4, the hiker can see a smaller, heart-shaped labyrinth. It is not nearly as elaborate as the Mazzariello Labyrinth, and apparently not as heavily used. There have been claims of other, earlier labyrinths hidden in the preserves , but Friends of the Labyrinth dismisses these as urban legends, as no evidence has been found. The organization reports that analysis of high-resolution aerial photographs show no trace of such activity. Visiting the park. The park is open year round. The park and gate hours are: There is no parking fee and no dog fee.