The Mother Lode in Mariposa County

The Mother Lode is not a single mine. It is a geological feature, a belt of gold-bearing quartz veins running roughly one hundred twenty miles through the western foothills of the Sierra Nevada, and Mariposa County occupies its southern end. The richest portion of Mariposa County's Mother Lode ran about twenty-four miles north to south through the county's center, and within that belt dozens of mines operated at various scales between the eighteen forties and the nineteen forties.

The first gold found in the area was placer gold, the loose flakes and grains that had eroded from the original quartz veins over millions of years and settled in creek beds where running water could concentrate them. Sonoran miners working the region in eighteen forty-nine found placer gold on Agua Fría Creek among the earliest Sierra strikes. Placer deposits were exhausted within a few years, which meant that anyone who wanted to stay had to switch to hard-rock mining, digging into the quartz veins where gold was still locked in the parent rock.

The Princeton Mine, located at Mount Bullion about four miles north of Mariposa, was considered the most productive mine in the county, with documented production of roughly five million dollars over its working life and a shaft sinking more than one thousand six hundred feet below the surface on an incline. A federal order in the fall of nineteen forty-two halted non-essential mining for the duration of World War Two, and most Mariposa County mines never reopened. The county's documented production from eighteen eighty to nineteen fifty-nine was roughly two million one hundred forty-four thousand ounces of gold.