Complex sentence: Officials were thinking of closing the bridge in the mid 1960s due to disrepair, then in 1970 a pedestrian threw a rock from the bridge onto a tour boat, and the bridge was closed.
Split into simpler sentences: Officials were thinking of closing the bridge in the mid 1960s due to disrepair. In 1970 a pedestrian threw a rock from the bridge onto a tour boat, and the bridge was closed.