This is Oak Tree House at Mesa Verde National Park, built by Native Americans in the year 1250 A.D. They left no written records, and no verbal history survived, so how do we know so precisely when it was built?
I took this photo during a boat ride on the Colorado River. I liked the way the canyon walls reflected in the water near the boat's wake. Since the water was crystal clear, why do you see the reflection of the canyon, instead of seeing through to the bottom of the river?