Complex sentence: Notable examples include the Filhiol Mound Site, located on a natural levee of the Ouachita River but the oldest and most significant in Watson Brake, the most ancient mound complex in North America, dated to 5400 BP (before present), or about 3500 BCE.
Split into simpler sentences: Notable examples include the Filhiol Mound Site, located on a natural levee of the Ouachita River. The oldest and most significant is Watson Brake, the most ancient mound complex in North America, dated to 5400 BP (before present), or about 3500 BCE.