Robert Sibley Volcanic Regional Preserve
The park was one of the first three parks established by the East Bay Regional Parks District (EBRPD) in 1936.[a] It was originally named Round Top Regional Park. Round Top (elevation 1,761 feet/537m) is an extinct volcano in the Berkeley Hills. It is home to several stone labyrinths of recent origin. The park was renamed after the second president of the EBRPD, Robert Sibley, shortly after his death. 
The preserve contains a Pliocene epoch volcanic center that, about 10 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 including 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 great 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. 
There are several trails in the preserve, with most restricted for hiking and horseback use. 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 are no campgrounds or picnic areas in the Preserve. The Visitor Center at the Skyline Boulevard entrance is unstaffed, but has displays depicting the areas geology. It also offers brochures to assist visitors making self-guided tours.
- East Bay Skyline Regional Trail, which is 31 miles (50 km) long, traverses the Sibley preserve on the ridgeline that separates between Wildcat Canyon Park 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.
- 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.
- The other two original parks were Tilden and Temescal.
- Moraga Formation — Pliocene epoch basaltic lava formation in park.
- Pliocene California geology
- Volcanism of California
- ebparks.org: Robert Sibley Volcanic Regional Preserve
- USGS.gov: "Upper Cretaceous and Lower Tertiary Rocks Berkeley and San Leandro Hills, California", by J. E. Case, GEOLOGICAL SURVEY BULLETIN 1251-J, 1968.
- Geology Blog: "Grizzly Peak and Moraga basalt"
- Geology.about.com: "California Transect - Stop 30, Orinda Formation and Moraga Volcanics"
- Lawrence Berkeley Lab.gov: "Berkeley Lab Geologist Studies the Ground Beneath His Feet"
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