Continuing business as normal, John Sutter dispatched associate James W. Marshall, who was to construct a sawmill in the foothills of the Sierra at the city of Coloma, in 1847. In January 1848, Marshall detected a flake of gold on the ground at the site of Sutter's new mill, and after conducting tests, determined the mineral's authenticity. Word leaked about the discovery nearly immediately. When news reached San Francisco, a rush of hopeful prospectors began to move northwards to the Sacramento Valley, and by the middle of the year, so-called "Argonauts" flooded Sutter's holdings in search of gold. The arrival of Argonauts in the region decimated the economical integrity of Sutter's New Helvetia, as the prospectors slaughtered his herds of livestock, drove out local Native Americans loyal to Sutter, and divided New Helvetia amongst each other without Sutter's consent. Disappointed with what had become of his holdings, Sutter placed his son as head of fort business operations and retired to Hock Farm.