Sutter's Mill gold was found on Mexican land in 1848

Gold was found at Sutter’s Mill on 24 January 1848, when carpenter James W. Marshall spotted bright flakes in the tailrace of a sawmill he was building for John Sutter at Coloma, on the South Fork of the American River in California.

We know the date largely because a mill hand wrote it down. Henry Bigler, one of the Mormon Battalion veterans working on the mill, recorded it in his diary, spelling and all.

“Monday 24th. This day some kind of mettle was found in the tail race that looks like goald, first discovered by James Martial, the Boss of the Mill.” — Henry Bigler’s diary, January 1848

The detail most accounts skip is whose land it was. California was still Mexican territory, occupied by US forces during the Mexican–American War. Nine days later, on 2 February 1848, the Treaty of Guadalupe Hidalgo transferred it to the United States — negotiated by diplomats who had no idea gold had just turned up in a millrace. Marshall and Sutter tried to keep the find quiet, but by May San Francisco was reported “half empty”, and the rush went national once President Polk confirmed the gold to Congress that December.

California in the gold rush	People
Non-Indian population, 1848	about 14,000
Coloma area, July 1848	1,000
California Trail emigrants, 1849 alone	25,000
California Trail emigrants, 1849–1854	about 140,000
Population by 1852	more than 200,000

The rush made California, but not the two men at its centre. Prospectors overran Sutter’s land, and by 1852 his agricultural colony of New Helvetia was ruined; he died in 1880 still petitioning Congress for compensation. Marshall never struck it rich. The state legislature granted him a $200-a-month pension in 1872, later halved and ended in 1878, and he died in 1885 working a blacksmith’s shop near Kelsey. For the Nisenan and Miwok people of the Coloma valley, already devastated by disease, the miners’ seizure of their fishing and gathering sites was a catastrophe.