Fact 1: Most canyons are formed by flowing rivers through erosion over long periods of time.

Fact 2: Geological erosion is natural occurring erosion over long periods of time.

Given the two facts above, answer the question "Most canyons are formed by rivers flowing and what type of erosion?" with the following options: 
- forces
 - mechanical
 - uncontrolled
 - geological
 - Water expanding
 - flooding
 - thrust
 - barrel-shaped


 

    geological     