The Sandhills sit atop the massive Ogallala Aquifer; thus both temporary and permanent shallow lakes are common in low-lying valleys between the grass-stabilized dunes prevalent in the Sandhills.
Paleoclimate proxy data and computer simulations reveal that the Nebraska Sandhills likely had active sand dunes as recently as the Medieval Warm Period, when temperatures in the North Atlantic region[REF][REF] were about 1°C (1.8°F) warmer than the current climate.