Isolated distant summertime thunderstorms can frequently cause flash floods events in regions free of clouds. The total amount of rainfall accumulates in the unvegetated landscape by quickly swelling the creeks. Within the geological time frame the erosion caused by these creeks is able to carve out deep slot canyons. To the inexperienced hikers flash floods usually occur out of the blue and suddenly fill canyons with dirty water full of deadly debris. Thereby the walls of the canyon gets further sanded and polished. This often results in optical illusions. Here, it is difficult to tell the stones from the holes in the canyon wall.
Canon 20D, EF-S 10-22mm, f/22, 1sec, ISO 100, tripod