The Lewis and Clark Expedition (1804-06) was the first American group to cross the Rocky Mountains and sail down the Snake and Columbia rivers to the Pacific Ocean. Meriwether Lewis supposedly became the first American to sight the drainage basin of the Snake River after he crossed the mountains a few days ahead of his party on August 12, 1805, and sighted the Salmon River valley (a major Snake tributary) from Lemhi Pass, a few miles from the present-day site of Salmon, Idaho. The party later traveled north, descended the Lemhi River to the Salmon and attempted to descend it to the Snake, but found it impassable because of its violent rapids. The expedition named the Snake River the Lewis River, Lewis's River, or Lewis Fork, in his honor, and they traveled northwards to the Lochsa River, which they traveled via the Clearwater River into the lower Snake, and into the Columbia. They also referred to the Shoshone Indians as the Snake Indians, which became the present-day name of the river. The name Lewis Fork, however, did not last.