Robert Sibley Volcanic Regional Preserve

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Robert Sibley Volcanic Regional Preserve
Sibley Volcanic Regional Preserve - Stierch A.jpg
Round Top, an extinct volcano at Sibley Volcanic Regional Preserve
LocationAlameda and Contra Costa Counties, California
Nearest cityOakland, California
Coordinates37°51′18″N 122°12′12″W / 37.85495°N 122.20326°W / 37.85495; -122.20326Coordinates: 37°51′18″N 122°12′12″W / 37.85495°N 122.20326°W / 37.85495; -122.20326
Area928 acres (3.76 km2)
Operated byEast Bay Regional Park District

Robert Sibley Volcanic Regional Preserve is located in the Oakland Hills of the East Bay region of the San Francisco Bay Area, California.[1] The park is part of the East Bay Regional Parks District (EBRPD), covers 928 acres (3.76 km2), 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.[1]


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 [537 m]) 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.[1]


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.[2][3][4] 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.[5]


A view from Round Top

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.[1]

Hiking trails[edit]

  • East Bay Skyline Regional Trail, which is 31 miles (50 km) long, traverses the Sibley preserve on the ridgeline that separates Wildcat Canyon Regional Park and Anthony Chabot Regional Park.
  • Round Top Road goes from the Sibley visitor center to the peak of Round Top. CLOSED
  • 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.[1]


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,[b] it is a favorite destination for hikers who come to pray, meditate, and examine talismans left in the center by previous visitors.[7] 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.[6]

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.[7]

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.[6]

Visiting the park[edit]

The park is open year round. The park and gate hours are:

  • November - February 7AM - 6PM
  • March - October 7AM - 10PM

There is no parking fee and no dog fee.[1]

See also[edit]


  1. ^ The other two original parks were Tilden and Temescal.[1]
  2. ^ Helena Mazzariello is a sculptor, psychic, and shamanic practitioner who lived in Oakland's Montclair District. The labyrinth she created is known as The Sibley Labyrinth, or "Mazzariello's labyrinth"[6]


  1. ^ a b c d e f g "EBRPD - Sibley". Retrieved 2021-05-11.
  2. ^ "Upper Cretaceous and Lower Tertiary Rocks Berkeley and San Leandro Hills, California", by J. E. Case, GEOLOGICAL SURVEY BULLETIN 1251-J, 1968.
  3. ^ Oakland Geology Blog: "Grizzly Peak and Moraga basalt"
  4. ^ "California Transect - Stop 30, Orinda Formation and Moraga Volcanics"
  5. ^ Chao, Julie (2010-07-06). "Berkeley Lab Geologist Studies the Ground Beneath His Feet". News Center. Retrieved 2021-05-11.
  6. ^ a b c "Mazzariello's Maze." Friends of the Labyrinth. Undated Accessed July 13, 2018
  7. ^ a b Jones, Nicole. "Sibley Regional Preserve: A walk on Oakland’s wild and volcanic side." Oakland North. July 22, 2011. Accessed July 13, 2018.

External links[edit]