Late summers at Bryce Canyon are marked by the monsoon season. Desert monsoons are different than those of India. They drop far less rain, but like those in India, are predictable in their afternoon arrival time. Every afternoon in late July and early August, rainstorms pass through Bryce Canyon. In the same way dry sponges absorb less water than moist sponges, the very dry rock and soil at Bryce Canyon absorb little water, allowing most of the rain to flow into joints, which cleans out the broken gravel left by frost wedging in the winter--thereby creating slot canyons. Runoff is the chief cause of erosion in the park.
Frost wedging and runoff are the two main processes that form walls, fins and landforms at Bryce Canyon National Park. Continued rock destruction and removal by these processes will eventually result in windows and hoodoos as the walls and fins become thinner. The China Wall on the Fairyland Loop Trail illustrates this evolution very well. The outermost portion of the wall is mainly hoodoos because it has been exposed to the forces of weathering and erosion longer than the side of the wall that is closest to the canyon rim. Yet even on the canyon rim side, you can see how the windows become increasingly smaller as you near the rim.
Some fins, like The Alligator which can be seen underneath , are capped with a more resistant form of limestone called Dolomite. This rock is reinforced with magnesium and cannot be dissolved by the weak carbonic acid that dissolves regular limestone. The hard rock above protects the weaker rock below, creating very durable fins.
