Model of a Canyon

Team Gibbas scientists were given the task of modeling the processes that formed the Grand Canyon over time.  Students began by layering red, white, yellow, and tan sand into a cut half gallon milk container.  Next students propped the milk container onto books and slowly poured water through a funnel.  Students were able to assimilate their prior knowledge about weathering, erosion, deposition and what they witnessed with the model to write some insightful explanations about how the Grand Canyon was formed.

Question:  How do you think the Grand Canyon was formed?