On December 7, 1805, the expedition encamped at the site they selected for their winter quarters. It was desirable for the availability of game, proximity to the ocean for salt-making, and moderate temperatures. Clark sketched a preliminary site plan of two parallel rows of cabins joined by gated palisades on either end. But with construction well under way on December 13, the design had clearly been altered. Ordway wrote, “we raised another line of our huts and began the last line of our huts forming three [sides of a] Square and 7 rooms 16 by 18 feet large. the other Square we intend to picket and have gates at the 2 corners, So as to have it a defensive fort.” Fort Clatsop was completed by January 1, 1806. When the expedition finally departed on March 23, 1806, Whitehouse wrote a parting description: “Fort Clatsop is situated on the South side of Columbia River, and about 1½ Miles up a small River […] and lay a small distance back, from the West bank of said River. The fort was built in the form of an oblong Square, & the front of it facing the River, was picketed in, & had a Gate on the North & one on the South side of it.”
After 1806, Fort Clatsop gradually diminished through natural deterioration and active removal.
By the 1850s, all surface traces had disappeared. Later efforts to verify the fort’s site culminated in archeological excavations in 1948. A reconstruction of the fort, based on Clark’s unrealized sketch, was completed in 1955. The site was designated the Fort Clatsop National Memorial in 1956, and then the Lewis and Clark National Historical Park in 2004. The 1955 reconstruction burned down in 2005; a replacement was completed in 2006.