Robert Sibley Volcanic Regional Preserve
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Robert Sibley Volcanic Regional Preserve is located in the
Oakland Hills Oakland is the largest city and the county seat of Alameda County, California, United States. A major West Coast port, Oakland is the largest city in the East Bay region of the San Francisco Bay Area, the third largest city overall in the Bay A ...
of the
East Bay The East Bay is the eastern region of the San Francisco Bay Area and includes cities along the eastern shores of the San Francisco Bay and San Pablo Bay. The region has grown to include inland communities in Alameda and Contra Costa counties ...
region of the
San Francisco Bay Area The San Francisco Bay Area, often referred to as simply the Bay Area, is a populous region surrounding the San Francisco, San Pablo, and Suisun Bay estuaries in Northern California. The Bay Area is defined by the Association of Bay Area Go ...
,
California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
. The park is part of the East Bay Regional Parks District (EBRPD), covers , and lies east of
Oakland Oakland is the largest city and the county seat of Alameda County, California, United States. A major West Coast port, Oakland is the largest city in the East Bay region of the San Francisco Bay Area, the third largest city overall in the Bay A ...
, partly in
Alameda County Alameda County ( ) is a county located in the U.S. state of California. As of the 2020 census, the population was 1,682,353, making it the 7th-most populous county in the state and 21st most populous nationally. The county seat is Oakland. Alam ...
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 The East Bay Regional Park District (EBRPD) is a special district operating in Alameda County and Contra Costa County, California, within the East Bay area of the San Francisco Bay Area. It maintains and operates a system of regional parks which ...
(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
labyrinth In Greek mythology, the Labyrinth (, ) was an elaborate, confusing structure designed and built by the legendary artificer Daedalus for King Minos of Crete at Knossos. Its function was to hold the Minotaur, the monster eventually killed by t ...
s of recent origin. The park was renamed after the second president of the EBRPD, Robert Sibley, shortly after his death. U.C. Berkeley Professor Emeritus
Garniss Curtis Garniss H. Curtis, (born May 27, 1919 – died December 19, 2012) was a professor of geology at the University of California, Berkeley, geochronologist, volcanologist, geophysicist, and founder of the Berkeley Geochronology Center. In 1960, Curt ...
studied the Sibley Regional Preserve extensively, dating the volcano to be 10.2 million years old. Since 10.2 million years ago, the Pacific tectonic plate has slowly pushed the volcano north.


Geology

The preserve contains a
Pliocene epoch The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Tilden Regional Park Charles Lee Tilden Regional Park, also known as Tilden Park or Tilden, [], is a regional park in the East Bay (San Francisco Bay Area), East Bay, part of the San Francisco Bay Area in California. It is between the Berkeley Hills and San Pablo R ...
to [ oraga. Geologists refer to this local volcanism as the Moraga Volcanics.USGS.gov: "Upper Cretaceous and Lower Tertiary Rocks Berkeley and San Leandro Hills, California"
by J. E. Case, GEOLOGICAL SURVEY BULLETIN 1251-J, 1968.
Subsequent compressive strains produced by various local faults such as the
Hayward Fault The Hayward Fault Zone is a right-lateral strike-slip geologic fault zone capable of generating destructive earthquakes. This fault is about long, situated mainly along the western base of the hills on the east side of San Francisco Bay. It runs ...
folded the lava-bearing rock formations, tilting the Round Top vent complex on its side. The results of such compressive strains of local faults has altered the volcano's original landscape, and Round Top now tilts towards the east. Such local faults, notably Hayward and
Moraga Moraga is a List of municipalities in California, town in Contra Costa County, California, Contra Costa County, California, in the San Francisco Bay Area. The town is named in honor of Joaquín Moraga, member of the famed Californio family. As ...
, have also caused the volcano to form a trough that is the Siesta/Gateway Valley. Folding, erosion, and a quarry operation exposed a cross section of the volcano, providing an excellent means to study a
California Coast Ranges The Coast Ranges of California span from Del Norte or Humboldt County, California, south to Santa Barbara County. The other three coastal California mountain ranges are the Transverse Ranges, Peninsular Ranges and the Klamath Mountains. P ...
volcano. The construction corporatio
Kaiser Sand & Gravel
used the region as a quarry, leaving the volcanic region open and exposed. Lava within the vent has been dated by
UC Berkeley The University of California, Berkeley (UC Berkeley, Berkeley, Cal, or California) is a public university, public land-grant university, land-grant research university in Berkeley, California. Established in 1868 as the University of Californi ...
at 9.5 million years old.


Rock Formations

The region has remnants of rocks from the
Orinda Formation The Orinda Formation is a Miocene epoch geologic formation in the Berkeley Hills of the East Bay region of the San Francisco Bay Area, California.Claremont Formation Claremont may refer to: Places Australia *Claremont, Ipswich, a heritage-listed house in Queensland * Claremont, Tasmania, a suburb of Hobart * Claremont, Western Australia, a suburb of Perth ** Claremont Football Club, West Australian Footba ...
. From the Orinda Formation rocks include "river gravel, sandstone, and mudstone." The river gravel are red in color. The sandstones are around 65 million years old. From the Claremont Formation, rocks include marine rocks. The surface of the
basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...
found on the
dike Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes ...
of Round Top are of the color "light brownish or rusty gray" and the interior of the basalt is of the color "gun steel blue."


Bake Zone

A bake zone is a region where heat from the lava of the volcano changed the color of the surrounding rocks to red. Such rocks include rhyolite tuff, lapilli agglomerate, and vesicular basalt. Rhyolite tuff are remnants of ash from a northern volcano around 4 miles away. Lapilli agglomerate are remnants of volcanic cinders. Vesicular basalt are remnants of gas bubbles from cooling lava.


The Stone Property

The Stone Property is a restricted region of the park. The area consists of pure basalt around 100 feet wide, as well as "autobrecciating basaltic flow" which occurs when lava continues to flow under a cooled surface.


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.


Hiking trails

* East Bay Skyline Regional Trail, which is long, traverses the Sibley preserve on the ridgeline that separates
Wildcat Canyon Regional Park Wildcat Canyon Regional Park is a East Bay Regional Parks District park bordering the city of Richmond in Contra Costa County in the San Francisco Bay Area of California. It includes a portion of Wildcat Canyon as well as a portion of the adjoin ...
and
Anthony Chabot Regional Park Anthony Chabot Regional Park is a regional park in Oakland, Alameda County, California in the United States. It is part of the East Bay Regional Park District system, and covers in the San Leandro Hills adjacent to Oakland, San Leandro and Cas ...
. * 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.


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.Jones, Nicole. "Sibley Regional Preserve: A walk on Oakland’s wild and volcanic side." ''Oakland North''. July 22, 2011.
Accessed July 13, 2018.
In this labyrinth, she would walk her goats, stating that, "I can enter with a question, and inevitably, I will emerge with some insight. It is a powerful spot." 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: * November - February 7AM - 6PM * March - October 7AM - 10PM There is no parking fee and no dog fee.


See also

* Moraga Formation — Pliocene epoch
basaltic lava A mafic mineral or rock is a silicate mineral or igneous rock rich in magnesium and iron. Most mafic minerals are dark in color, and common rock-forming mafic minerals include olivine, pyroxene, amphibole, and biotite. Common mafic rocks include ...
formation in park. * *


Notes


References


External links


"Friends of the Labyrinth" website. Accessed March 8, 2019.

EBparks.org: Official Robert Sibley Volcanic Regional Preserve website
{{East Bay Regional Parks Sibley Volcanic Sibley Volcanic Sibley Volcanic Sibley Volcanic Geology of Alameda County, California Geology of Contra Costa County, California Pliocene California Volcanism of California Parks in the San Francisco Bay Area