In 1834 Parker answered a call for missionaries to move to the American West brought about by four Flathead tribesmen asking William Clark for religious guidance.

[1] After preaching at the Green River rendezvous of the American Fur Company, Parker continued west while Whitman returned east.

[1] During the winter of 1835 to 1836, Parker was a guest at the Hudson's Bay Company's fur trade outpost on the Columbia River, Fort Vancouver.

[1] Parker then left the region by ship, sailing first to the Sandwich Islands and then around Cape Horn to the Eastern Seaboard.

[3] He published a book in 1838 describing his journey to Oregon, Journal of an Exploring Tour Beyond the Rocky Mountains.