The Gold Country is a historic region in the northern portion of the U.S. State of California, that is primarily on the western slope of the Sierra Nevada. It is famed for the mineral deposits and gold mines that attracted waves of immigrants, known as the 49ers, during the 1849 California Gold Rush.GeologyThe Gold Country lies on the western slope of the Sierra Nevada, reaching down to the Sacramento Valley. The oldest geology can be found along the easternmost portions of this region, closer to the Sierra Nevada summits. It consists of ancient sea floor and portions of islands which were added onto the western edge of North America during the late Paleozoic, about 275 million years ago. The western sections of the Mother Lode are significantly younger, from the mid Mesozoic about 150 million years ago, and also consist of material that was solidified on the ocean floor to the continental edge. Massive intrusions of granite forced their way into these formations. After ten miles of overlying material was eroded over the last 70 million years, these intrusions became visible throughout the Sierra Nevada. Over the last 50 million years, rivers and volcanoes deposited materials; these built up in thick layers found atop many of the high ridges of the Sierra Nevada foothills.
