On the evening of November 4, 1805, the Corps of Discovery camped in the vicinity of today’s Post Office Lake. Clark recounted, “I could not Sleep for the noise kept by the Swans, Geese, white & black brant, Ducks &c. on a opposit base, & Sand hill Crane, they were emensely numerous and their noise horrid.” The following day they passed through a broad, channeled floodplain “covered with cotton wood, maple, and the like kinds of wood” and bounded by ridges “closely covered with spruce timber.” An abundance of wildlife included a variety of birds “flying in every direction,” sea otters, snakes, and deer. There were “a great many Indian camps, their lodges made chiefly of poles and cedar bark.” Particularly notable was the Chinookan village of Cathlapotle, which Clark described as “a large village, the front of which occupies nearly ¼ of a mile fronting the Chanel, and closely Connected, [with] 14 houses in front.” During the return journey, the Corps stopped to visit the village on March 29, 1806. They delayed for about three hours, bartering and purchasing goods. Clark “gave a Medal of the Small Size to the principal Chief” before they departed.
The Ridgefield National Wildlife Refuge, which includes Post Office Lake, was established in 1965 to provide a habitat for wildlife – particularly wintering waterfowl. The 5,300-acre refuge also preserves numerous archeological sites that span over 2,000 years of occupation, including Cathlapotle. A full-scale Chinookan plankhouse, based on evidence found at the Cathlapotle archeological site, was constructed in 2005 to interpret the refuge’s natural and cultural history.