On January 24, 1848, while working on construction of the mill, Marshall found flakes of gold in the South Fork American River. On February 2, 1848, before news of the discovery had arrived, the Treaty of Guadalupe Hidalgo was signed in Mexico City. This peace treaty formally transferred sovereignty over the region to the United States. Two workers at the mill, Henry Bigler and Azariah Smith, were veterans of the Mormon Battalion and recorded their experience in journals. Bigler recorded the date when gold was discovered, January 24, 1848, in his diary. Sutter's claim to the US government for mineral rights was investigated by Joseph Libbey Folsom, who issued confirmation the gold discovery in June. The first flake found by Marshall was shipped to President James K. Polk in Washington DC, arriving in August 1848. It is now on display in the National Museum of American History, part of the Smithsonian Institution.