Robert Sibley Volcanic Regional Preserve

Robert Sibley Volcanic Regional Preserve is a beautiful park in the Oakland Hills of the East Bay region in the San Francisco Bay Area, California. This park is part of the East Bay Regional Parks District and covers a large area of 928 acres. It is located east of Oakland and stretches partly into Alameda County and Contra Costa County.

Visitors can enter the preserve from Oakland using Skyline Boulevard, or from Contra Costa County using Old Tunnel Road. The park offers many chances to explore nature and enjoy the outdoors.

History

The park was one of the first three parks established by the East Bay Regional Parks District in 1936. It was originally named Round Top Regional Park, after an extinct volcano in the Oakland Hills. The park was later renamed after Robert Sibley, the second president of the EBRPD, after his death. A professor from U.C. Berkeley studied the park and confirmed the volcano is about 10.2 million years old. Since then, the Earth's tectonic plates have slowly moved the volcano northward.

Geology

The Robert Sibley Volcanic Regional Preserve has a special volcanic area from about ten million years ago. This old volcano created lava that formed the East Bay ridges, stretching from Inspiration Point in Tilden Regional Park to Moraga. Local faults, like the Hayward Fault, moved and tilted these lava rocks over time.

The park offers a great chance to see inside an old volcano. While the mountain Round Top isn’t the volcano itself, the ancient volcano has worn away, leaving interesting rock formations exposed. Scientists from UC Berkeley found that some lava here is about 9.5 million years old.

Rock Formations

The area contains rocks from two old formations. The Orinda Formation includes red river gravel, sandstone, and mudstone, with some sandstones being around 65 million years old. The Claremont Formation has marine rocks. The basalt on Round Top’s dike appears light brownish or rusty gray on the surface and gun steel blue inside.

Bake Zone

A “bake zone” is where heat from the volcano changed nearby rocks to a red color. These rocks include rhyolite tuff from an older volcano about 4 miles away, lapilli agglomerate from volcanic cinders, and vesicular basalt from gas bubbles in cooled lava.

The Stone Property

The Stone Property is a special, restricted part of the park. It features pure basalt about 100 feet wide and an area where lava kept flowing under a cooled surface, creating a unique rock formation.

Activities

The preserve has many trails for hiking and horseback riding. Most trails are for these activities only, but a few can be used for other purposes. Round Top Road is paved from the visitor center to the top of Round Top. There are no picnic areas, but there are benches for resting and having a snack, plus a campground. The visitor center at the Skyline Boulevard entrance does not have staff, but it offers brochures for tours you can guide yourself. It also shows pictures of the area's rocks and land.

Hiking trails

• East Bay Skyline Regional Trail is a 31-mile-long trail that goes through the Sibley preserve along the ridge between 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 goes around the peak of Round Top.
• Volcanic Trail was once a road used for carrying away rocks from a quarry and has stops for a self-guided tour about volcanoes.
• Quarry Trail links the middle of Volcanic Trail to a lower part of Quarry Road.
• Pond Trail is a short path that leads down to a couple of small lakes on the north side of the preserve.

Labyrinths

There are at least two man-made labyrinths in the preserve. The first, and most visited, is called the Mazzariello Labyrinth. It was built in 1990 by a local woman named Helena Mazzariello as a gift to everyone. Many hikers visit to think, pray, or look at small items left by others in the center. Helena used to walk her goats there and said it helps people find answers.

A little further along the Round Top Loop Trail, there is a smaller, heart-shaped labyrinth next to the Volcanic Trail. It is simpler and not used as much as the Mazzariello Labyrinth. Some people say there might be more hidden labyrinths, but no proof has been found.

Visiting the park

The park is open all year. From November to February, the park is open from 7AM to 6PM. From March to October, it is open from 7AM to 10PM. There are no parking fees or dog fees.