Doing urban geology in a place like Oakland adds a new question to the mental checklist that cannot be bypassed: “Is this truly a natural feature?” A boulder may be imported. A terrace may be an old railroad bed. Sibley Volcanic Reserve is a former quarry, therefore it’s safe to assume that this huge pit is not natural and that the labyrinth, one of several in the park, is of even later vintage. But park staff and other visitors have told me that some people insist, against all persuasion, that the labyrinths were made by cosmic visitors.
There is something about human beings, isn’t there? I used to trouble myself over our ability to believe nonsense, but now I realize that banging my head against that wall just hurts my head, and the wall likes it. The fact is, the general run of people love to be amazed. The trouble is, they aren’t particular about what amazes them.
Don’t get me wrong about labyrinths—they are good to experience, they do things to your head, they help pull you out of tedium. That’s cool. I think that crediting them to space aliens is a failure of imagination and a poor reflection on human ingenuity. What amazes me about labyrinths is that we invented them.
But what amazes me more satisfyingly is that people could examine this ground and figure out that it used to be the insides of a small basaltic volcano, now tilted onto its side. It takes imagination first, then the perseverance to test your imagination against the rocks again and again until every question you can think of has been met with a reasonable answer. I haven’t done that at Sibley, but having been to geology school I know how to do it if I set my mind to it. The people who did do that amaze me. They used directed imagination and rigorous skepticism instead of listening for voices and watching for signs, unhuman as that is.
Oakland Geology 
12 July 2008 at 9:55 am
I just went on that hike last week and was wondering about that labryinth … now I know it’s aliens ;)
Now that I live in the East Bay, I’ve been using this blog for planning my future East Bay hikes … thanks!
13 July 2008 at 2:29 pm
Hi Andrew,
I walked in Tilden a few times, on the Wildcat Gorge trail running below Lake Anza. On the left side, you see some major rocks that look very volcanic with large openings. I’m curious if this is possible?
Thanks,
Debby
13 July 2008 at 7:22 pm
Debby, I’m not yet familiar with the Wildcat Canyon trail, but the stream runs through nonmarine sedimentary rocks of the Orinda Formation on both sides. The openings are probably related to weathering, like you see on Mount Diablo where an outer shell of the rock is hard but underneath it’s less well cemented, so it weathers out in pits. The official geologic name for this kind of formation is tafoni. But as I said, I haven’t walked that trail yet.
15 July 2008 at 9:31 am
I used to go up to that quarry in the winter to see if the pond had frozen over; it was fun to slide rocks across and break the ice. I was irritated when someone built the labyrinth, but what the heck.
There’s a lot of interesting stuff to see as you go down that canyon, and if you skirt south into Huckleberry reserve there’s even more intersting remnants of human occupation. There’s some truly ancient old cars in a remarkable state of preservation on the backside of the ridge.
21 October 2008 at 3:09 pm
I’ve been told there are 4 labyrinths here at the park. I’ve only found one with luck. I haven’t found the one pictured above. Does anyone have explicit directions of how to get to this one? Or, do you know of any guided tours to get there? I’m a true labyrinth lover, but not at all fond of hiking in circles. I really like to know where it is I’m going.
I’ve noticed that none of the Park’s literature even mentions or directs you to the labyrinths, why I don’t know. Yet, it would seem reasonable that they would and could. Any help/guidance is really appreciated? Thanks!
[Look for the huge pit. Also, it’s easily visible in Google Maps. The park’s literature doesn’t mention the labyrinths, and rightly so, because they’re not one of the natural or cultural features the preserve was created to protect. — Andrew]