The Lewis and Clark Expedition made the first documented descent of the Columbia River from the mouth of the Snake River to the Pacific, strengthening the young United States' claim to the lands of the Columbia River Basin against England, which had never fully accepted Captain Robert Gray's 1792 American claim by maritime entry into the Columbia. The Corps of Discovery entered the Columbia at the mouth of the Snake River on October 16, 1805, established twenty-four camp sites on its 325-mile downriver dugout canoe voyage, and explored and mapped tributaries of the Columbia as well as plains, mountain ranges, and valleys along the route. The men of the expedition and the Indian woman Sacagawea successfully negotiated the river's rapids and cataracts, then at its broad estuary endured raging storms, turbulent waters, and near starvation before reaching the Pacific Ocean in mid-November 1805. The explorers gathered information on the Indian tribes who lived along the river and on the flora and fauna of the river corridor, and this documented description of the rich river region later lured pioneers crossing the continent to settle in the Oregon Territory. The expedition built Fort Clatsop near present-day Astoria, wintered there, and in March 1806 began the return trip up the Columbia, the first leg of the long journey home.