In the literature relating to Fort Vancouver there seems to be some uncertainty as to the site where the Hudson's Bay Company (HBC) built their water-powered sawmill, which was in operation as of 1828. Reproductions circulate of a painting by John Mix Stanley dating from c. 1853, showing the mill beside a stream next to a bluff:
If you travel on the old Evergreen Highway along the Columbia River, about 6 miles east of Fort Vancouver and just east of the present Interstate 205 bridge, you will find a large sign between the highway and the railroad track, across the road from the existing Columbia Springs Trout Hatchery:
The bluff depicted in Stanley's painting is still visible above the stream, but the construction of the trout hatchery (by the Civilian Conservation Corps in the 1930s) has drastically altered the landscape and probably obliterated most of whatever archaeological evidence there might be for the old sawmill.
More on the early history of the Fort Vancouver sawmill can be found in the Cultural Landscape Report on the Park's website.
There is an excellent article on the history of the Fort Vancouver sawmills in the HBC magazine "The Beaver," which has been digitized and made available online. The article by Donald Clark is called "Sawmill on the Columbia," published in June, 1950. Just click on the title to read it and/or save it to your hard drive.