Complex sentence: Sierra Madre was hit by a M 5.8 earthquake at 7:43 AM PDT on June 28,1991, which did regional damage, such as knocking over chimneys and rearranging cinder block walls, such as those which run along major roads in the area.
Split into simpler sentences: Sierra Madre was hit by a M 5.8 earthquake at 7:43 AM PDT on June 28,1991. The quake caused regional damage, such as knocking over chimneys and rearranging cinder block walls that run along major roads in the area.