Just looking for general tips. I'm not asking you to do my job for me.
Use a multitap delay. Work out how far each surface is from the sound source, then calculate how long the sound would take to return from each surface and use these numbers for each tap, finally pan the taps so that each surface has the correct orientation and relative signal strength, further away should be quieter. Then mix in with original signal.
One thing that always helps to get something in a special Place -> Reverb/Impulse Response Reverbs. One thing so -> Don't always think you need a big reverb for wide locations. Sometimes small reverb create a better image of a big wide place, imho.
If you want go get your hands dirty -> Go into a wide,rock canyon (or similar, maybe a stadium etc.) and record/re-record the sounds there.
Another thing is atmosphere. By adding wind or nature atmosphere (maybe soaked in reverb) you give the hearer a stronger bond to the canyon.
In addition to the points already made, do remember that much of the rock/canyon sounds on TV and film are far from authentic. I spend a lot of time hanging around on rocks and the real sound effect is much more subtle.
Much of the time in film and TV all the sound effects tend to be over emphersised to make the point.