Argyilan said similar holes have been reported in migrating dunes at the Oregon Dunes National Recreation Area in Florence, Ore., and Silver Lake State Park in Mears, Mich., but the holes at Mount Baldy provided the first opportunity to directly study them. Ten holes had been found in the dune when her research was published. The deepest was the 10-foot hole that the boy fell into, but most were a yard or less deep, she said.