Imagining the landscape that is the San Francisco Peninsula looked in bygone times is one of my favorite pastimes. Seeing the world from this perspective turns everyday places into historical gems that provide a view of a former landscape. They are the living clues that connect to the stories of the areas that surround them that have changed. Some are well documented, others are not, and are in need of some educated guesses. One of these latter type places is a local legend, The Crystal Cave of San Bruno Mountain.
We adventured to this hidden piece of history, on assignment of sort, for Everything South City. We were very fortunate to have an experienced miner, Roger Cain, in our company of three when we went to explore the Crystal Cave of San Bruno Mountain. I have been to the cave several times, but this was the first time that we had a person of such knowledge involved, and the first time we agreed to document our little expedition.
“These tailings indicate that this was definitely man made, probably done by hand (pick axe). Although this wasn’t a large operation, there are probably records of this somewhere” Roger, our prospecting hobbyist said staring at the piles of quartz crystal infused rocks that lied outside the cave and then down the cliff to the creek below. “At some point they would have had to cut a trail clear up this valley, large enough to bring animals and equipment up” he added. Roger was not positive that they were looking for gold, but that that was his theory. He noted they may have been looking for other minerals, but he doesn’t believe they found anything, as the mine was abandoned, leaving behind what is now known as the Crystal Cave. Also, had they found gold, they would have had to crush the ore on site or carry it out to a place where they could separate the gold from the rock. The cave roughly measured is around 30 feet deep and about six feet tall and hard rock all the way.
Roger explained that when miners are looking for gold they often look for quartz, that gold and quartz are synonymous. When they found a gold vein and the ore was crushed, the gold would be extracted either by panning the gold or by leeching it out from the rock using quicksilver (mercury). To this day the creeks in San Jose are polluted with mercury and there are relics of the quicksilver mines in the hills, remnants of the prospecting economy that dominated our region a little over a century ago. The Crystal Cave tells stories of a time when mining speculators were looking for gold on San Bruno Mountain.
All but the trailhead to the Crystal Cave was grown over and although there was evidence of recent past human habitation (a weathered sleeping bag) it was clear that no one had ventured to the cave in months.
The trail to the cave crosses a spring led creek fed by the underground aquifer beneath San Bruno Mountain. This small waterway cut The Devil’s Arroyo, the name of the valley where the cave resides. What was left of the trail was grown over by many local plants. A large portion of these plants are poison oak and stinging nettles. This proved to be a challenge for us, as was the slippery steep climbs. The trail follows the creek and then shoots up the hillside, leaving the creek behind. It was fortunate for us that adventurers in years past had installed a network of ropes to traverse the mud and rock hill, and although we brought along ropes of our own, we did not need to use them. Of all the times I have been to the Crystal Cave due to the thick overgrowth of nettles and poison oak, this was by far the most treacherous.
We made it to the cave relatively unscathed and feeling a little more alive than when we started. As we stared down The Devils Arroyo into civilization less than a mile beyond, we felt the ironic feeling that although we were standing in what felt like wilderness, civilization was in very close proximity.
After Roger explained the likely history of this hole in San Bruno Mountain, I pointed at the trail that continued. It is very grown over now, but I explained the trail eventually meets up with the creek again. Then the creek comes to a rock wall that is roughly fifteen feet high, and covered in moss as the creek disperses itself down its face. Above this wall is a small cliff where the creek comes out of the hillside. Resting, and staring at the nettle infested trail, we decided to not make the final leg of the journey on this day. Instead we took a roundabout trail to the top of the cave, and it was clear from this vantage point that the line of orange quartz runs vertically down the hillside. We rested and admired the quartz crystals and the wildflowers. Then we started the journey back to the urban environment we came from.
The three of us who made this trek consider ourselves environmentalists, the type who “leave only footprints, take only pictures” so we did seriously discuss not writing about our little adventure. Ultimately we decided that the article should be written. To those that may be upset about the confirmation of this local legend that we would like to note that our photos purposely left out any
landmarks that that could be used to triangulate its location. Also, the trail being as overgrown and filled with Poison Oak and stinging Nettles as it was, we thought it unlikely that anyone would make such a journey simply to fulfill bad intentions.
Local legends and history are important. They connect us to the places we live and connect us together as the history of this place we live belongs to all of us. That is why history is one of the broader themes of the Open the SF Watershed movement, so we can explore and tell the tale to our children the colorful history of the San Francisco Peninsula. What you see, and what is beneath your feet has a few stories to tell, once you know them, they are yours forever.
-Andy Howse, Editor Open the SF Watershed
Roger Cain contributed to this article
If anyone has any documents to the history of these mines/caves, we’d be interested to hear about them so we can continue this story. Please share here or contact EverythingSouthCity@gmail.com
Because we have heard many say they want to climb the mountain and explore and search for the cave this added information is important. Please take heed.
We would like to add a warning to this story for those who may go out searching on the mountain.
*To be successful you must be in good health and physically fit
*Do not go alone, always bring another person with you
*Let others know your plans before you head out
*Dress covered head to toe to protect yourself from Stinging Nettles and Poison Oak.
*Bring water & emergency supplies including rope, gloves, etc
*Carry in, carry out. Leave nothing behind but your footprints. Always respect the Mountain