1.   The lake was formed by geologic upheaval.

2.   Before the lake was formed, Rainbow Bridge National Monument was visited by only several hundred people a year, who arrived on foot or on mule.

3.   The lake had been formed by a glacier receding at the end of the last ice age.

4.   The Chaima Indians had other ideas about how the lake was formed.

5.   Thurston reckons the reason has to do with the way the lakes were formed.