Beginning roughly 400 million years ago and for over 200 million years much of California was being formed. Plate tectonics were slowly spreading the ocean floor until it subducted (sank) below the continent of North America. During this process parts of the ocean floor, some carrying gold placed by underwater volcanism, accreted (accumulated) onto the North American landmass. Around 160 million years ago the docking of Smartville, a gold rich island arc, created much of what is today know as California's Mother Lode.
It is this unique geologic history that made the Gold Rush possible. Most of our planet does not contain the quantity of highly consolidated gold that made California the hot spot it became. These gold rich gravel beds are responsible not only for the influx of people to the California coastline but also for a host of breakthroughs in technology engineered for the specific needs of extracting the gold from the often hard to reach places. Check back again for more on the people and technological advances of the California Gold Rush.