Turning northward Frémont reached, on September 18, 1843, Fort Hall, Idaho, then a post under British control, whose original importance as an Indian trading-post had been greatly enhanced by its location on the emigrant route to Oregon, at a distance of over one thousand three hundred miles from the then frontier settlement of Westport, Mo. Following closely the emigrant trail Frémont, on October 8th, passed Fort Boisé, then occupied by the Hudson Bay Company, and on the 25th of the month arrived at another trading establishment of this company, at the junction of the Walla Walla and Columbia Rivers. This was considered by emigrants as the practical termination of their overland journey since navigation down the river was rapid and convenient. Frémont found many American emigrants at Fort Vancouver on his visit to that post and also learned that others already occupied the adjacent lowlands of the Willamette Valley. Moreover, these pioneers were not confining their efforts to Oregon, for while small parties were pushing southward through that valley to settlements in Northern California, still others, making detours near Fort Hall, reached, by a more direct route through passes in the Sierra Nevada, the banks of the Sacramento. On November 10, 1843, Frémont left Vancouver to return to the United States, having in view an entirely new route whereby he might be able to complete the exploration of the great interior basin between the Rocky Mountains and the Sierra Nevada. His party then consisted of twenty-five. Leaving the Columbia at a point above The Dalles, Frémont followed Des Chutes River to its source, and passing over to Lake Klamath, contemplated a journey to and a winter camp on either Mary's Lake or the mythical Buenaventura River. His trail brought him to Lake Klamath, and later to Goose Lake, the source of the Sacramento. Winter had now commenced; the weather in the mountains proved to be extremely cold, snow-storms became frequent, and his search for Mary's Lake and Buenaventura River proved fruitless and dangerous.