We followed the ridge for a while, then dropped into the dry gorge. Seasonal flash floods had carved an amphitheater, huge, cool, and dim. The east rim, where the low sun struck, was brilliant yellow against the cobalt sky.

The floods had rolled big stones around and around until they drilled deep holes into the bedrock. One shaft was nine feet deep. How many millennia of intermittent rains does it take to scour a pit like that?