Rock Fort Campsite is the site where the Lewis and Clark Expedition camped twice, one on their journey to the Pacific and the other on their return trip home. They spent three nights beginning on October 25, 1805 and for three nights beginning on April 15, 1806. They chose the location because its round rock formation provided a natural defensive position. It was here that the expedition made its first contact with the Chinook-speaking peoples. The celestial observations Lewis and Clark took of the site as well as their description of the location helped researchers to confirm the exact spot of the campsite. The site is just past the Celilo Falls. Their stay here allowed them to rest, hunt new game, dry their goods and repair their boats. The site was listed on the National Register of Historic Places in 1980.