Sibley Volcanic Regional Preserve

This is uncanny. We are standing here looking east at the basaltic remains of the bottom of the top of a volcano, and behind us is the base. Off to the left and right are the ash deposits of the flanks. We are right in the middle of the thing!…the middle of a volcano that, ten million years ago, spewed ash and fire onto the landscape. Steve Edwards points to a geologic feature
That volcano is Round Top, conveniently located in the Sibley Volcanic Regional Preserve in the Berkeley Hills. And we were there on the May 19 CCM&GS; field trip to see it up close and personal.

According to our field trip leader, volcanologist Steve Edwards, the volcano, which was once upright, and all the sediments and structures of the region were tilted to near vertical and transported hundreds of miles northward from its origins near Hollister. The volcano now lies on its side and has been eroded so that you can literally stand inside the ancient structure.

Steve said there is no other place on earth, save going to a live volcano, where one can see and learn the characteristics of volcanism.

After listening to Steve’s explanations, there is little wonder he is considered the foremost authority on Round Top. Much of what is known about Round Top was explained by Steve, through 15 years of study and geologic mapping of the area. In fact, it is largely through Steve’s work that the Sibley Regional Preserve was renamed the Sibley Volcanic Regional Preserve.

We could not have asked for a more knowledgeable, thorough, and lucid guide than Steve. His understanding of the region, the basalts, the landscape, and even the small nuances of volcanism, some of which eluded other scientists for decades, is immense.

By the accounts of all, the field trip was a resounding success. Many are looking forward to the next. Marie, a guest from Castro Valley Mineral & Gem Society, was impressed that our club had such interesting field trips.

We walked on mostly gentle pathways for nearly four miles on an out and back course. Steve took us to the most interesting formations at the furthest points, which are in an area not accessible to the public.

According to my GPS, we spent an equal time walking and stopping and averaged a leisurely two miles per hour. There was plenty of time for resting and listening. Most of the 26 attendees who joined before the tour for coffee and donuts rejoined after lunch for a pleasant debriefing.

The weather was superb, the guide was fabulous, and we could not have asked for more. Join us for the next one.