The low ditches between the ridges are called swales. These swales are between 65 and 100 feet wide. They were created when people dug soil to build the ridges. It is hard to say if the swales served a purpose aside from making the ridges taller. One thought is that the swales could have collected water during heavy rains (image right). This may have kept people's homes drier.

     A narrow rise that crosses a shallow depression outside the southwestern section of the ridges is called the causeway. The causeway is about 295 feet long and almost 50 feet wide, but probably originally went across the entire depression. Archaeologists are not sure what the causeway was for. Perhaps it was the path people used to get the soil for maintaining the plaza.

Archaeologists have had a hard time telling why people built the ridges in a C-shape. After all, there is nothing else in the world like them! Some think there were symbolic reasons, maybe related to spiritual beliefs. Others think that building the ridges helped create a sense of community at the site.