Not sure about nationally, but it's long-running and near top of BiG rivalries, with combination of first year + # of meetings (1891, 113 meetings) ...No way they leave out Minnesota if there are three protected rivals. Isn't Floyd of Rosedale the oldest trophy game?
Even with that isn't 1st. (but close)
Paul Bunyan's Axe: 1890, 127 meetings.
Old Oaken Bucket: 1891, 121 meetings.