You are presented with the question "What was formed through erosion over long periods of time?" and the following answer choices: 
- Columbia River Gorge
 - a hydraulic system
 - swamp vegetation
 - Mississippi River delta
 - the Moon
 - Calcium carbonate
 - the Himalayan mountains
 - permineralization

Now knowing that most canyons are formed by flowing rivers through erosion over long periods of time and the Columbia River Gorge is a spectacular river canyon cutting through the volcanic rock of the Cascade Mountain Range, choose the best answer.


 

 Columbia River Gorge        