After several years in St. Louis he moved west to Independence, Missouri, where he had extensive contact with settlers headed west to Oregon. In 1843 he headed west himself, as a member of Captain John Fremont's expedition, and decided to remain in Oregon while Fremont went on to California. Here Gilpin helped the Willamette Valley settlers organize a government and draft a petition requesting congressional support, a petition which Gilpin himself carried back east. And when he finally delivered the Willamette petition to Congress in 1845, he produced a report on his travels that emphasized the rich potential for trade with Asia that American settlements along the Pacific would provide. Gilpin served with distinction during the Mexican-American war as a member of the force that bloodlessly conquered New Mexico.
Empire plants itself upon the trails.
In later years Gilpin developed his vision of manifest destiny into an elaborate plan to use a network of railroads to unite the world into one economic and cultural whole, under the control of the United States. Gilpin joined the Republican party in the wake of the Kansas crisis, and although this was not a popular affiliation in Missouri, it helped him win appointment as the first territorial governor of Colorado. Here he helped raise troops for the Union during the Civil War, including the First Colorado Volunteers who won a critical Union victory at Glorietta Pass in 1862 . To finance these troops, however, Gilpin issued drafts on the federal treasury, and when questions were raised about the propriety of his actions, he was removed from office. Unfazed, Gilpin devoted the latter half of his life to land speculation, using his firsthand knowledge of the West to locate and secure enormous land grants in the Southwest that had been inherited from the time of Spanish rule.