When did Lewis and Clark reach the Rocky Mountains?

Answer 1

They reached it after discovering the source of the Missouri River at Three Forks, Montana.

Answer 2

In spring 1805, they continued to the headwaters of the Missouri River, struggled across the Continental Divide at Lemhi Pass, and headed west along the Salmon, Clearwater, Snake, and Columbia Rivers to the Pacific. They landed at the mouth of the Columbia River, Astoria, Oregon on November 7 1805. The day was rainy and foggy, and the Columbia River estuary was four or five miles wide and they could not see the Oregon side of the river or Point Adams at the mouth of the river in the distance. But they were close enough to have reached their goal.

Answer 3

They reached St. Lewis on September 23, 1806....BTW they left to find the Missouri River a year after that...