
Construction of the mill began in the fall of 1847. On January 28, 1848, the mill was half done, and James Marshall was inspecting and working on tailrace. In one section of the tailrace Marshall noticed several pieces of gold and gathered them to show to Sutter. The team at the mill and Sutter all inspected the metal, and concluded that they had discovered gold.
Word of the discovery spread, and the California gold rush ensued with the waves of immigrants known as the forty-niners. Large number of prospectors and businesses moved into California to try to capitalize on the find, with many of the early miners and businesses finding opportunities to create significant wealth. California was somewhat of a lawless area at the time, and the influx of immigrants along with the lack of infrastructure and regulations led to various conflicts amongst the diverse cultures that ended up residing there including the indigenous people in the region. The great wealth in the ground drove industries in California that lasted well over 100 years, and the development of various technologies to improve and lower the costs of mining.