The canyon walls are largely sandstone of various hardnesses. You can see in the next three picture how easily some of it erodes.
The next two pictures show another characteristic of the Chocan culture. Notice the horizontal lines of large stones. We saw similar lines of green stones at Aztec.
This is one of the best pictures we have of the wall construction called "core and facade." The center of the wall is larger stones with a sand based mortar and the exterior is carefully aligned facing stones.
The round holes were support holes for wooden logs that supported the roof, or the floor of the next level above.
We were struck by what a beautiful job they did on this window.