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 towards the Pacific. They landed at the mouth of the Columbia River, Astoria, Oregon on November 5 1805. Lewis and Clark, sadly, did not actually see the Pacific Ocean.
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.
Clark makes a quick note the their reaction at the end of the journal entry for November 7, 1805:
"Great joy in camp, we are in view of the ocean, this great Pacific Ocean which we have been so long anxious to see. The roaring or noise made by the waves breaking on the rocky shores (as I suppose) may be heard distinctly."
The explorers began their journey home on March 23, 1806. On July 3, after crossing the Continental Divide, the Corps split into two teams so Lewis could explore the Marias River. Lewis and Clark stayed separated until they reached the confluence of the Yellowstone and Missouri Rivers on August 11. Once reunited, the Corps was able to return home quickly via the Missouri River. They reached St. Louis on September 23, 1806.