John C. Frémont was born out of wedlock in Georgia in 1813 after his mother Anne left her older husband for French Canadian tutor Charles Fremon. Expelled from the College of Charleston for irregular attendance, he found a patron in Joel R. Poinsett, taught math in the Navy and joined the Army’s Topographical Corps. He secretly married Jessie Benton, daughter of Missouri senator Thomas Hart Benton, who then backed his western surveying expeditions beginning in 1842. Guided by mountain men such as Kit Carson, Frémont mapped the Great Basin and showed that the rumored Buenaventura River to the Pacific did not exist, while Jessie turned his notes into widely read reports.

Sent west again in 1845 with secret instructions, he stirred up American settlers in Mexican California, and his forces attacked Native villages in violence historians now place within the California Genocide. After he refused orders from General Stephen Kearny, he was court martialed for mutiny and convicted before President Polk commuted the sentence. Gold on his Mariposa ranch made him a millionaire, he became one of California’s first senators, and in 1856 he was the first Republican presidential nominee. In 1861 Lincoln removed him from command after his unilateral emancipation order in Missouri. He lost his fortune in the Panic of 1873, governed Arizona Territory, and died in a New York boarding house in 1890.

• His Great Basin survey used barometric readings to show the region’s rivers drained inward into lakes and sinks.
• The government printed tens of thousands of copies of the expedition reports he coauthored with Jessie.
• He raised the U.S. flag on a mountain peak in Mexican California after being told to leave.
• He lost the 1856 presidential election to James Buchanan.
• After his death, Jessie Benton Frémont lived on a Civil War widow’s pension.