Geology Of The Mother Lode

Geology, Ancient History with a Modern Twist in the Mother Lode Cutline: Many buildings in the Mother Lode, like this one in Volcano, were made of limestone. By Sarah Lunsford Word count: 1,549 A drive through the Mother Lode reveals not only beautiful scenery and unique towns, but also a little bit of the way it was knit together. Quartz veins with their precious gold enticement drew droves of people to the area during the Gold Rush, but those veins were just part of a larger picture that gives the Mother Lode is landscape. “There’s such rich geologic history in the area that it’s quite an exciting area to be in,” said Russ Shoemaker, educator and owner of Stories and Stones. At one time, most of the area was part of an inland sea much like the Great Barrier Reef in Australia. “All of this area, during past geologically, was under the sea,” said Shoemaker. Visual remnants of that era are seen in the limestone that still exists. “Anytime you see limestone is evidence of coral reefs,” said Eric Costa, gold exploration geologist. Marble, a form of limestone, outcroppings can be seen around Columbia and Murphys as examples of what remains of those ancient coral reefs and where they were sutured onto the western edge of North America, said Costa. Later in time, continental plates meeting and overlapping coupled with volcanic activities gave the region another interesting layer of formations both over and underground. “The most interesting part of the Mother Lode is what you call a suture zone,” said Doug Keaton, mining engineer. This suture zone is the line where the plates collided then overlapped, from the East and West, at the end of the era of the dinosaurs. Where the two met, structures were pushed up and to the East that is why some vertical standing stones list in that direction. “You have a series of little micro plates being attached the larger plate,” said Costa. After these initial structures were eroded by time and elements, volcanoes erupted showering the area with lava and ash that ran through then existing rivers, streams and valleys, capping some structures with their deposits and artifacts underneath, such as Table Mountain in Tuolumne County. The Sierra Nevada’s are actually the youngest structures to be formed in this sequence of events. It was their own erosion process that revealed its gold deposits in the new rivers and streams, along with underground veins. There was so much upheaval that the new Mokelumne River that is seen today is actually 1,500 feet lower in elevation and miles away from the original. The collision point of the Mother Lode is found under Sutter Creek and Plymouth in Amador County and is marked by a change in stone from the East to the West. On the eastern side of the collision the dominant stone is greenstone while on the western side it is slate.

The greenstone can be seen dotted around the Mother Lode sitting vertically in clusters where is was pushed up on the sea floor in the form of pillow lava. The miners nicknamed it “tombstone rock” because of its resemblance to cemeteries with their tombstone grave markers. The tombstone rock can be found in Amador County at Sutter Hill near the CDF station there and neat the Italian Picnic grounds, as well as near the Calaveras County Airport. “The greenstone, it’s a really, really hard rock,” said Keaton, which is an explanation of how it ended up keeping its basic characteristics through all the geological turmoil that surrounded it. “It was in these cracks that the gold solution came up,” said Keaton. This gold solution ultimately became the Mother Lode which years later would draw so many people to the region. Although the Mother Lode region is not bound by manmade boundary lines, running from Mariposa County to the South up through Placer County to the North, it is defined into three belts with the primary belt running parallel to Highway 49 from Plymouth to Mariposa. This main gold belt is associated with the Melones Fault zone that served as a plumbing system for the gold solution that would become the main Mother Lode. The West gold belt was around the Hodson and Salt Springs Valley regions in Calaveras and minimally with regions of Amador and Tuolumne and was associated with the Bear Mountain fault line. The East gold belt is characterized with gold deposits associated with granite intrusions and is located in the Sheep Ranch, Railroad Flat and West Point areas of Calaveras. The Sutter Creek Gold Mine shows visitors the meeting point of two different gold bearing quartz ore bodies, the Lincoln and the Comet. “That’s an unbelievable cross section (of the gold formation),” said Costa about the underground offerings at the Sutter Creek Gold Mine. “(There’s an) intersection of major vein structures,” said Holly Boitano, environmental protection and safety coordinator, Sutter Creek Gold Mine. Those veins run vertically and horizontally. “The majority of the (surrounding) rock is greenstone,” said Boitano as an explanation of why the miners had a hard time getting through and taking out the gold. Some of the most spectacular deposits of crystalline gold in the world can be found around the gold mines of Sonora and Columbia, often referred to as pocket mines, said Costa. The largest crystalline gold specimen in the world can be found at Ironstone Vineyards heritage museum in Murphys where the 44-pound specimen, discovered by the Sonora Mining Company in 1992, can be viewed by visitors. Gold wasn’t the only substance of value the early miners found, they often found a girls best friend as well. “They found diamonds along with the gold,” said Keaton. Going further away from the epicenter of the collision of the Mother Lode found in Amador County softer stone is found in the form of serpentine. Many examples of serpentine, which is the official state rock of California, can be found in the Mother Lode.

A good example of this is near New Melones Dam in Calaveras, as well as places where natural terrain was cut for roads, such as the long straight away on Highway 49/12 driving from San Andreas to Jackson. “The gold belt is marked with serpentine,” said Costa. A mineral unique to the Mother Lode, Mariposite, a chromium mica, is associated with the serpentine rock in the gold belt, said Costa. The clay found in the Ione area of Amador is used in specialty clays used in to make bricks and ceramics and shipped around the world. This clay belt formed through volcanic and sedimentary process extends down into the Valley Springs area of Calaveras, and is only found in four other U.S. locations, Castle Rock, Washington; Whiteware, Montana, along with Hobart Butte and Mollala, Oregon. The clay in the area is not the local substance with a worldwide market, the Calaveras Cement Company located in San Andreas was known for producing the finest cement in the world from local limestone combined with shale and silica before its closure in 1983. It shipped cement that ended up in Pardee Dam and military bases such as Mare Island and Travis Air Force Base. Today another local limestone is popular more for its attractiveness than its utilitarianism. Murphys stone, a metamorphosed limestone with quartz inclusions, is a favorite of those who practice Suiseki, a form of Asian stone appreciation. Geological formations are not the only visible traces of what has happened through the years, there are plants that are typical of and unique to the Mother Lode region. “There are lots and lots of examples of really rare plants,’ said Pat Stone, member of the California Native Plant Society. The geological make up of certain area determines what plants grow in that area with some being unique because of a combination of factors including soil composition. Two onions in particular are only found in the region. The Rawhide Hill Onion is only found in five places in Tuolumne County and nowhere else in the world, while the Yosemite Onion is found around granite in the Yosemite Valley. The Tuolumne Fawn Lily is unique to that county growing only in granite soil and taking its name from its county of origin. “Serpentine, for most plants is poisonous,” said Stone. One of the exceptions to this is the Chinese Camp brodiaea a member of the lily family is grows in serpentine and volcanic soils and is found only in two places near the Chinese Camp School in Tuolumne and one other location in Calaveras. The volcanic clay around the Ione area in Amador County is home to two rare species. “The ones (plants) in Amador are really rare,” said Stone. “Both the Ione Manzanita and Irish Buckwheat, both only occur there.” Plants found only in this area because of the geological make-up are not limited to flowers and bushes, but include trees as well. The Sequoia Gigantea, commonly known as the Giant Sequoia is only found in the Western Sierra Nevada’s including Big Trees State Park in Calaveras County and grow in granite based soils. “Most of the special places we reserve for plants are special because of the geology,” said Stone.

From rock formations, to veins of gold, to plants, the geological formation of the Mother Lode has given everyone a taste of the past in the present, which is something one and all can enjoy while taking time to enjoy the natural treasures the area has to offer.