Grand Canyon carrier (4)
I believe the answer is:
mule
'grand canyon carrier' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for mule that I've seen before include "Slipper - beast of burden" , "Illegal drugs courier" , "Crossbreed" , "Sterile offspring of donkey and horse" , "Obstinate creature" .)