On a drive back from my girlfriends work, I happened to drive Carmel Valley Road back past Black Mountain in the Rancho Penasquitos area of northern San Diego. I decided to stop by and check out the road that led up the mountain, called the Miners Ridge Loop Trail View Map. At the top I briefly stopped and grabbed a pamphlet which had a map and some historical, as well as ecological, information about Black Mountain. As I was reading it I came across this:
In the 1920s, there was a short-lived boom in white arsenic because it was an ingredient in a pesticide that attacked boll weevils, which were infesting Southern cotton crops. Frank Hopkins, an Escondido rancher, rodeo cowboy and actor, used his Hollywood contacts to fund an arsenic mine on the north slope of Black Mountain. Several years of cold winters and dry summers in the South effectively eliminated the boll weevils, so demand for white arsenic fell. The mine was abandoned in 1927, but its concrete dust chamber, shafts and oven remain.
I had never heard of a mine in the area, so I decided to do a little investigation. After searching Google for a few minutes, I found little information about the mine, and even less about the location of it. Using the information from the pamphlet I gathered that it may be possible to spot the mining equipment left by using Google Earth, an explorer's best friend. A short while later, I found the shafts on the north side of the mountain, just a hundred feet or so off the path. GPS: 32.990164, -117.111308
Armed with this new information, I was determined to make it to the mine later in the day. I packed up my usual items and headed off to the trail head.
Upon arriving, I strapped on my new boots and headed off on the trail. Along the trail there are several different signs informing travelers of the different plants as well as Native American history in the area. To find the correct trail, if you can even call it that, is a bit tricky. From the parking lot, head left out a well maintained trail (1). Several hundred feet down the trail on the left side of the trail you will see a sign that states the trail that has been close off (2). Turn left at this point and head down slightly until you come to a little dirt area. Right where you turn left there is a very small trail that lets you keep going straight down (3). Follow this trail all the way down the top side of the mine flume (4).
The trail leading down to the top of the mine is very small and will take a lot of bushwhacking and effort to make it down. I would recommend wearing pants except on the warmest days to keep your legs from getting cut by the branches, and to help keep ticks off your skin. Once you reach the exhaust flume, you will see a large hole in the top of the flume. Peer in, but be careful not to fall in. Please do not walk down inside the concrete structure. It is very instable and you could be seriously injured or killed. Instead, carefully walk down the side of the mountain to the base of it. In 1926, the 180-foot-long concrete stack was constructed for processing the arsenic, which was then used for pesticide. The arsenic was mined, crushed, and heated to a vaporizing temperature. The condensed arsenic vapor was collected from the baffles inside the stack. If you peer in from the top or the bottom, the baffles are visible.
Just down from the flume is where all of the action happened. There is scattered concrete holding tanks, old metal pipes, collapsed buildings, an old brick oven and the collapsed mine. Unfortunately the years have not been kind to the old mine. It looks as if it has been collapsed for some time now, and the entrance is totally blocked by tons of rock and old wood beams. This is probably better because as you may know arsenic is very toxic. Elemental arsenic and arsenic compounds are classified as “toxic” and “dangerous for the environment” in the European Union under directive 67/548/EEC . There are other interesting areas though. Still left from the mining days is a old brick oven. It must have been the one used to heat the arsenic to create the vapors.
If you head up the valley there was are more mine shafts that you can enter. These are not full mines, as one only goes back about 25ft, and the other about 75ft. I believe these were some exploratory digs rather than the actual mine, which is collapsed. To get there, head southwest from the concrete flume (uphill) about 200ft. You will see a smaller hole in the rock to the right. This is the smaller of the two mines.
If you go just a few more feet up the hill, there is a path that leads to the left where there is an entrance to the bigger mine. This is the one that goes about 75ft into the mountain. There are some old wooden support beams laying on the ground. I posted a video on youtube of the two mine shafts.
If you go back down the valley (just down from the oven) are some concrete storage boxes, which I assume held the arsenic. The mine was a bit hard to get to, especially tracking down the location of it. On a scale of 1-5, I would give this a 3. I am happy I went there but probably wouldn't go there again. There isn't a whole lot to see, but it is worth the trip once for sure. There is some interesting history behind this mine and the operation of it. It can be dangerous, but if you stay off the structures and collapsed mine and just walk around, it isn't bad. The hardest part is just to walk through the shoulder high brush to get there.
As always, please be careful exploring and ALWAYS tell someone where you are going. Some dangers may include: ticks, torn up legs (from the bushes), arsenic poising, snakes, heat exhaustion and unstable structures. If you want any more information on this location, don't hesitate to contact me.