From the record
“Savanna Portage State Park is a state park in the U.S. State of Minnesota established in 1961 to preserve the historic Savanna Portage, a difficult 6-mile (9.7 km) trail connecting the watersheds of the Mississippi River and Lake Superior.”
Wikipedia article Savanna Portage State Park, CC BY-SA 4.0.
One of 10 National Register listings published here for Aitkin County · listed in 1973 · category: Site · built in 1961.
Sources: the Wikipedia article · the case file at the National Archives · the National Register database, National Park Service