Still, it’s much cooler than hiking here in summer, when fierce midday heat often blankets the hills of Almaden Quicksilver County Park. The mile or so hike up the Randol Trail-a wide dirt path that the Mexican and Cornish miners who once worked here knew as Metal Road-has left me sweating on this unseasonably warm winter day. The definitive source for historic and geologic information on the area is the classic US Geological Survey Professional Paper 360, "Geology and Quicksilver Deposits of the New Almaden District.Beneath the shade of bigleaf maples, bay laurels, and valley oaks, I rest beside a natural spring near the caved-in mouth of Day Tunnel. New Almaden cinnabar is notable for its tiny crystals that give the ore a glittering appearance. This is the only way you can acquire New Almaden specimens today, unless a dealer is selling off a historic collection at a rock and mineral show. The little museum shop has cinnabar from the Guadalupe Mine for sale. The Casa Grande has rooms full of period furnishings as well as the Quicksilver Mining Museum. The mining museum housed in the Casa Grande, the old manager's residence built in 1854, is full of exhibits and is well worth a visit if you can be there during its brief open hours. Mount Hamilton's observatories stand out beyond the lower Santa Teresa Hills, site of more mercury mines and sandstone quarries. The top photo of this post shows the view west to the Sierra Azul, and to the east are views of the Santa Teresa Hills and Diablo Range. I don't see the problem with that, and if I could make the rules I would give rockhounds access to limited parts of the park.ĭon't miss the views of the surrounding territory. A ranger told me that if people kept taking things home with them, eventually there would be no tailings left. Remember that collecting rocks and minerals is forbidden. Although this shaft produced only minor amounts of ore, the rocks themselves are interesting. Nearby are extensive piles of mine tailings. The Buena Vista shaft mainly served to dewater the hills and allow neighboring mines to go deeper in search of cinnabar. The foundation of the pumphouse is constructed of large blocks of local sandstone and Sierran granite. Veins in the San Cristobal tunnel.Īnother worthwhile spot is the site of the Buena Vista shaft, the deepest in the district. These are typically filled with quartz or dolomite. Go on in and look for the veins in the walls. San Cristobal tunnel, first opened in 1866. One mine entrance, the San Cristobal tunnel, has been kept open for a short distance. Serpentinite boulders in a streambed.Īmong other things, the park contains mines and machinery spanning a century of progress from traditional techniques of medieval origin to modern American facilities. As you hike about the ridge, keep an eye underfoot for the widespread serpentinite. The cinnabar lodes, in turn, were emplaced in and near the silica-carbonates. These fluids, derived from magma intrusions, replaced the minerals in the serpentinite and turned it into silica-carbonate rock. It's kind of a mess, and the details are in the caption, but basically Los Capitancillos Ridge is like many other Bay Area mercury sites, an intricate mixture of Franciscan rocks and serpentinite that has been kneaded and heated and injected with metal-bearing fluids. Units with names starting Q, T or K are younger. Franciscan rock units are fm, melange fpv, volcanics gs, greenstone pink, serpentinite yellow, silica-carbonate rock orange, chert. The New Almaden district runs northwest on Los Capitancillos Ridge from the village of New Almaden. Let's look at the geologic map of the area (derived from USGS Map OF-98-975). Although mining ended in the 1970s, geologists believe that much undiscovered ore remains. A hundred years later, the mines had yielded mercury in the amount of more than a million flasksa volume of the liquid metal weighing 76 pounds. Its name, New Almaden, echoed the famous Almadén mines of Spain. Soon afterward the New World's richest quicksilver mining district began production, supplying the mercury for the refiners of the California Gold Rush. In 1845 a Mexican visitor recognized the substance as cinnabar or mercury ore. Like other ancient peoples around the world, they used it as a pigment. The first Californians mined a deep-red ore they called mohetka in the heights of Los Capitancillos Ridge. Today Almaden Quicksilver County Park is a rugged playground for hikers, bicyclists and equestrians, but lovers of geology and mines have a special kind of fun there. In the foothills due south of San Jose sit the remnants of California's first mining bonanza, the New Almaden mercury district. View west from Almaden Quicksilver County Park toward Loma Prieta, highest peak of the Sierra Azul.
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