Captain John C. Frémont completed two interior scientific expeditions (1842 and 1843-1844), which opened the West to American emigration.[123][124][h] In his 1842 expedition, Frémont boldly climbed a mountain in Wyoming, Frémont's Peak (13,751 feet), planted an American flag, and symbolically claimed the Rocky Mountains and the West for the United States. [126] In his second expedition starting in 1843, Frémont and his party entered Oregon following the Oregon Trail. Traveling west on the Columbia River, Frémont sighted the Cascade Range peaks and mapped Mount St. Helens and Mount Hood.[127] In early March 1844, Frèmont and his party descended the American River valley to Sutter's Fort in Mexican California.[127] Given a cordial greeting by John Sutter, Frémont talked to American settlers, who were growing numerous, and discovered Mexican authority over California was very weak.[127] Upon Frémont's triumphal return from his second expedition, at General Winfield Scott's request, Tyler promoted Frémont with a double brevet.[128][i]

Florida
On Tyler's last full day in office, March 3, 1845, Florida was admitted to the Union as the 27th state.