Orinda, California 94563, United States
Ten million years ago, lava flowed from an active volcano through the hills of the East Bay, with flows reaching from the Inspiration Point of Tilden Park to Moraga. Today, the Round Top volcano-rising 1,763 feet above sea level-is the most prominent characteristic of the Sibley Volcanic Regional Preserve. The preserve was dedicated in 1936, and is one of the oldest parks in the East Bay Regional Park District. The area was once the hub of massive quarrying activities, and the preserve today is best known for the enigmatic labyrinths that existed at the bottom of the canyons of the quarry.
This 2 1⁄2-mile walk takes you past two of the labyrinths. The preserve is a common dog-walking location, and you'll see several dogs, mostly well-behaved and on leash. There's a fair amount of cows, too, so watch where you step.
Round Top Loop Trail
Take a brochure and map from the visitor centre. If you wish to do a self-guided tour, there are numbered stops inside. An interpretive display displaying various types of volcanic rocks is also in the visitor centre. Take the uphill trail to your right (as you face the Visitor Center). The trail is wooded, with plenty of live oak eucalyptus, fir, bay and shore, and then opens to the east for views through the valleys.
Then the main road bends to the left toward the water tower. Continue here on a smaller, but still paved, road to the right. Do not take the first marked cutoff to the right, which will take you through Huckleberry Preserve on the Bay Area Ridge Trail. Instead, take the second cutoff to the right to remain on a smaller, more rocky route, the Round Top Loop Track. The forest disappears just past a cattle gate, and you are in grassland and rolling hills. Climb the short distance to the top of the hill to see views that can reach the Sierra Nevada on a clear day, when you see a thin footpath on your right.
Go through a T junction on the Round Top Loop Road. There is a fenced overlook straight ahead, where you can look down into a dark quarry. Until that was Round Top Volcano's Guts. Quarrying however removed the lava and created this huge pit, creating a great opportunity for geologists and others to see and study the interior of a volcano.
From the top, the largest and most complex of the labyrinths is visible, and it's the only one that we know for sure hasn't been created by aliens. It is the Mazzariello labyrinth which was built as a gift to the world in 1989 by East Bay resident Helena Mazzariello. It is a true labyrinth, meaning it has only one route to the middle rather than a labyrinth providing several options. You can take the trail down to the labyrinth, or walk (with care) along the top of the quarry, peering into its depths.
Switch back to the Round Top Loop Trail to see a second labyrinth before it turns to the left to complete its loop. Continuing straight onto the Volcanic Road, once the path to the quarry haul, experience Tilden Park views. When the Quarry Trail intersects to the left, a numbered post will appear, matching the numbered stops on the self-guided tour. The second labyrinth is Number 5 (Older Maps No. 7). Look down the quarry to a delicate, heart-shaped labyrinth, smaller and maybe more elusive than the first.
Continue along the Volcanic Trail to see the remaining numbered stops on the self-guided tour or return to the Round Top Loop Trail, bearing the right to complete the loop and return to the car park.