Geochemistry Question:

The simplest way to answer this is to define each term, so you can see:
1) A canyon is a deep valley with steep sides thinks of the Grand Canyon most famously to visualize what this is.
2) A gorge is a deep ravine, which usually has a river running through it – though this does not have to be the case.
3) Finally, a valley is any depression, usually of a certain length, in the surface of the land and often contains a river.
Therefore, a canyon is a specific type of valley, with particularly steep sides. A gorge is a deep depression that will usually contain a river.