After a group of Nez Perce and Bitterroot Salish men journeyed to St. Louis requesting the Book of Heaven in 1831 (their people had heard of it years before), Lee and his nephew Daniel Lee volunteered to serve as missionaries for them. Both were appointed as missionaries by the church, given orders to open and maintain a mission among the Salish. At the time, the Pacific Northwest was "jointly occupied" by the United Kingdom and the United States as agreed to in the Treaty of 1818. The missionaries went overland in 1834 with Nathaniel Jarvis Wyeth, an American merchant who previously visited the Columbia River basin to enter the regional fur trade market. The party of priests and fur trappers arrived at Fort Vancouver later that year and were greeted by Chief Factor John McLoughlin. While there, McLoughlin influenced Jason Lee to open the station among the Kalapuya in the Willamette Valley rather than the Salish.