Complex sentence: M-65 has been relatively slowly developed, and it was one of the last Michigan state highways to be completely paved--a stretch in Alcona County and Alpena County was gravel until 1961.
Split into simpler sentences: M-65 has been relatively slowly developed, and it was one of the last Michigan state highways to be completely paved. A stretch in Alcona County and Alpena County was gravel until 1961.