The reason the Mormon farmers who first settled and named Zion Canyon eventually sold it to the the federal governmemt for a park was the threat of flash floods. They grew tired of their crops and their homes being swept downstream every decade or so. The Virgin River is a beautiful and kind lady at all times except when she isn't. Capitol Reef Natioal Park has a similar history.
The spectacular scenery of the American West is all very much "a work in progress." Much of it is the work of run away erosion, flash floods, earthquakes, volcanic eruptions, fires, violent weather and other catastrophes. If it were not so, it would look like Austrailia.