Most canyons are formed by flowing rivers through erosion over long periods of time, and deep canyons and valleys are carved out. Given these facts, what are formed by flowing rivers through erosion over long periods of time among the following options:
- deserts
 - a hydraulic system
 - deep valleys
 - pyramids
 - Calcium carbonate
 - patch reefs
 - buildings
 - Sediment


 

   deep valleys      