Until recently, what Oaklanders would call the “back side” of Sibley Volcanic Regional Preserve was officially off-limits. But about a year ago, the East Bay Regional Park District opened a trailhead just off Fish Ranch Road that makes a whole new segment of the park accessible to the public.
The route to the trailhead is just through the Caldecott Tunnel. By car, take the first exit, which turns sharply back towards Oakland. Continue straight up Old Tunnel Road a few hundred yards and you will see park district signs directing you to Quarry Road. (If you continue a little farther on Old Tunnel Road, you will reach one of the entrances to the Skyline Trail.)
Some of you may consider what follows to be more of a hike than a walk. Quarry Road, which is broad and paved, rises 200 feet in a little under a mile: not an impossible grade, but certainly one you will feel in your thighs. The hills around you are covered in yellow-flowered broom and the occasional modest-sized oak, and your route is open to the sun and sky.
A half-mile from the parking lot, or just about the point you may be tempted to turn around, the road makes a sharp S-bend, and a guidepost on the right points you through a cattle gate to the unpaved fire road called the Quarry Trail. This path, which is significantly more level, gives you a clear view of the Round Top Creek valley, a good place to look for raptors, although this morning it was the private domain of a lone hummingbird, who disdained to give way to the passing hiker as he sunned himself on a bare twig.
If you want a longer excursion, stay on Quarry Trail until it joins the Volcanic Trail, a sharp left turn about a half-mile from the cattle gate. This loops back to the summit of Quarry Road. Or continue a little farther to the Round Top Loop Trail — although most walkers will prefer to approach that from the Oakland side.
More information: About Sibley Volcanic Regional Park, and about the volcano. In fact, Andrew Alden’s OaklandGeology blog has several posts about Sibley, but he doesn’t use categories or tags, so the easiest way to find them is through Google.
Cool stuff nearby: When you return to Oakland by turning left on Fish Ranch Road to cross Highway 24, be sure to appreciate the Art Deco ornamentation over the original tunnel entrance. Other than a portable toilet in the parking lot, there are no nearby services.