In the thirties, religious enthusiasm was added to the profits of the fur trade as an inducement to visit Oregon. By 1832 the trading prospects had incited migration outside the regular companies. Nathaniel J. Wyeth took out his first party in this year. He repeated the journey with a second party in 1834. The Methodist church sent a body of missionaries to convert the western Indians in this latter year. The American Board of Foreign Missions sent out the redoubtable Marcus Whitman in 1835. Before the thirties were over Oregon had become a household word through the combined reports of traders and missionaries. Its fertility and climate were common themes in the lyceums and on the lecture platform; while the fact that this garden might through prompt migration be wrested from the British gave an added inducement. Joint occupation was yet the rule, but the time was approaching when the treaty of 1818 might be denounced, a time when Oregon ought to become the admitted property of the United States. The thirties ended with no large migration begun. But the financial crisis of 1837, which unsettled the frontier around the Great Lakes, provided an impoverished and restless population ready to try the chance in the farthest West.
A growing public interest in Oregon roused the United States government to action in the early forties. The Indians of the Northwest were in need of an agent and sound advice. The exact location of the trail, though the trail itself was fairly well known, had not been ascertained. Into the hands of the senators from Missouri fell the task of inspiring the action and directing the result. Senator Linn was the father of bills and resolutions looking towards a territory west of the mountains; while Benton, patron of the fur trade, received for his new son-in-law, John C. Frémont, a detail in command of an exploring party to the South Pass.
The career of Frémont, the Pathfinder, covers twenty years of great publicity, beginning with his first command in 1842. On June 10, of this year, with some twenty-one guides and men, he departed from Cyprian Chouteau's place on the Kansas, ten miles above its mouth. He shortly left the Kansas, crossed country to Grand Island in the Platte, and followed the Platte and its south branch to St. Vrain's Fort in northern Colorado, where he arrived in thirty days. From St. Vrain's he skirted the foothills north to Fort Laramie. Thence, ascending the Sweetwater, he reached his destination at South Pass on August 8, just one day previous to the signing of the great English treaty at Washington. At South Pass his journey of observation was substantially over. He continued, however, for a few days along the Wind River Range, climbing a mountain peak and naming it for himself. By October he was back in St. Louis with his party.