Opening in 1872 and worked over the next 90 years, the Rinconada Mine was once one of the largest producers of mercury in San Luis Obispo County.
A sign along West Pozo Road will guide you to the trailhead and parking area, which are located at the end of a short gravel road on the west side of the highway.
The main trail starts near the east end of the parking lot. There’s also a shorter trail located on the west side of the lot which provides an easier and faster route to the abandoned mine and mercury processing mill ruins.
We were in the mood for something a little more challenging, so we started our hike at the east end of the parking lot and hopped on the Rinconada Trail. You can connect this trail with the Little Falls and Big Falls trails to form a longer scenic loop but since we were running short on time, we stayed on the Rinconada and proceeded to make our way up the mountain.
Since we were hitting the trail in the dead of summer, the first half mile or so wasn’t that exciting.
Our goal was to make it to the open pit on top of the mountain and then down its western slope to check out what’s left of the mill.
We didn’t expect to be exposed as much as we were along the route, so it was a little difficult fighting off the heat and glaring sun as we made our way up the mountainside.
As we climbed further up the mountain and closer to the actual mine site, nearly every piece of rock we passed showed at least some of the characteristic red color that cinnabar is known for.
People began using cinnabar for pigments thousands of years ago in Italy, Greece, Spain, China, Turkey, and the Mayan countries of South America. Through time, people in almost every country where volcanoes are present discovered cinnabar and realized its utility as a pigment. Cinnabar is one of a very small number of minerals that was independently discovered, processed and utilized by ancient people in many parts of the world.
Cinnabar is the chief mineral composed of the element mercury, and is a very important ore mineral. The vast amounts of it that were discovered here kept the mine in production for over 90 years.
A central gallery was dug out of the mountain, opening to the sky from above and leading to ore chutes below. From there the ore was loaded into ore cars and taken over to the mill for processing.
It’s difficult to capture just how big the open pit actually is but if you look at how small the ladder looks in the picture above you can get a pretty good idea of its massiveness.
The mine itself includes over 7,000 feet of tunnels.
Below the pit, on the western side of the mountain, sits the remains of the mill machinery that once processed the ore at the Rinconada Mine.
When the cinnabar ore came out the mine, it was dumped through a “grizzly,” a grid of iron rails, which took out the larger boulders before the ore dropped into the crusher.
The crushed ore was then stored in a 150-ton bin to await treatment.
As the rotary furnace turned, the ore moved toward the heat at the lower end.
The heat turned the mercury to vapor before it was drawn into the pipes of the condenser.
Historical photos show what the process looked like back in the 1960’s.
As the mercury was drawn from the condenser it was put into flasks (metal cylinders) which held 76 pounds of mercury each.
Total production from The Rinconada Mine was about 3,000 flasks or approx. 228,000 pounds worth of mercury.
Of course, mining for mercury is a dirty and extremely toxic process.
So from 2003-2008, the EPA made efforts to clean up the site.
All of the adits and shafts were supposedly closed off in 2004. Because the composition of the rock at most of the adit entrances weren’t conducive to anchoring metal gates, polyurethane plugs were installed. By 2005, vandalism had removed or compromised the integrity of most of the plugs.
So in 2008, they collapsed the arch over the main pit, blasted shut even more entrances into the mine and even installed a bat gate at in one of the main tunnels. All of which failed to keep people from gaining access into the mine.
I actually found one of the ways into the mine while we were hiking, but it required an extremely tight squeeze between numerous boulders, a crawl through a 16″ culvert that eventually shrinks down to 12 inches in diameter and lots of other highly questionable tight spaces.
We could’ve spent hours exploring the area but since we had to get back to LA before nightfall and were facing a major traffic nightmare ahead of us on the 101, we only had another 30 minutes or so to enjoy the ruins and history that lay before us.
Instead of hiking back the way we came in, we decided to follow a trail that started at the mill and eventually lead us back to the western end of the lot where we parked.
Taking this route definitely saved us some time but the thorny, dead vegetation that lined this portion of the trail was a killer on the legs.
Fortunately, the route eventually opened up into a lovely shaded woodland area before reaching the parking lot. If only our drive home could of been as lovely.