Studies of mineral formations found in caves in the walls of the Grand Canyon and nearby may provide fresh insight into the chasm's history, including its age and the rate at which it was carved.
Many of these caves contain mammillaries, mound-shaped lumps of carbonate minerals that typically form just below the surface of mineral-rich pools. Thus such deposits mark the level of the local water table, says Carol Hill, a geologist at the University of New Mexico in Albuquerque. If the water table drops—due, say, to changes in climate or tectonic movements of Earth's crust—the formation will be left high and dry. By measuring the concentrations of uranium and lead in a deposit's outer layers, researchers can estimate