High Quality Content by WIKIPEDIA articles! M-73 is a north–south state trunkline highway in the Upper Peninsula of the US state of Michigan. It connects with US Highway 2 (US 2) and Highway 55 (WIS 55) at the state line near Iron River. Running through forest, the highway was first designated along with the rest of the state highway system in 1919. Unchanged since its inception, M-73 was completely paved by the mid 1930s.