From the record
“The Stone Bridge is a causeway built by the United States Army in 1867. It crosses the marshy channel that connects Hart Lake and Crump Lake in a remote area of Lake County in eastern Oregon, United States.”
Wikipedia article Stone Bridge and the Oregon Central Military Wagon Road, CC BY-SA 4.0.
One of 14 National Register listings published here for Lake County · listed in 1974 · category: Structure.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service