Looks more like he was using the sun low on the horizon, could be other formations blocking the sun to give a selected illumination. Then dodge and burn to even things out, maybe masking. Some of his other works look like the were defiantly masked. There are lots of ways of getting that effect (if you know what you are doing) with out artificial light, good eye good timing, could of used reflectors on some who knows......and large format gives you that incredible depth.
It wouldnt be too hard to do similar with Erics canyon pictures, just would require a bit more dodge and burn.