Complex sentence: The trunkline turns east on Jackson Street, running next to the Negaunee City Hall, which was built in 1914--15 at a time when the city's population was increasing and iron production was peaking.
Split into simpler sentences: The trunkline turns east on Jackson Street, running next to the Negaunee City Hall. City hall was built in 1914--15 at a time when the city's population was increasing and iron production was peaking.