From the record
“Fort Klamath was a military outpost near the western end of the Oregon Trail, between Crater Lake National Park and Upper Klamath Lake in Klamath County, Oregon, United States. The Fort Klamath Site, about a mile southeast of the present community of Fort Klamath, Oregon, is listed on the U.S.”
Wikipedia article Fort Klamath, CC BY-SA 4.0.
One of 28 National Register listings published here for Klamath County · listed in 1971 · category: Site · built in 1863.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service