From Annabel's earthform texture I was inspired to look at natural canyon formations that occur in America. I specifically researched the rock formations that create walkable shallow canyons within the crust. Because of the thick layers that stack and curve around the gaps, very little light shines through, and as the sun moves throughout the day the angle of approach continuosly changes which is interesting because certain areas that we're shadowed for the entire day are lit up, and areas that have been lit for the most of the day can become cold and sheathed in the afternoon.

Jump to 2:02 to see the amazing formations that I'm talking about


Here's another video, although not as good:

http://www.youtube.com/watch?v=DJF-sEh7hjA&feature=related