Carcross Sand Dunes, Yukon, Canada. Mountainous rain shadow makes this area arid. Although some have called it the "world's smallest desert" (1 square mile of sand dunes), the Carcross Dunes are actually too humid to be a true desert. Its sand comes mainly from nearby Bennett Lake, a former bed of a Pleistocene glacial lake. The exceptionally rare Baikal Sedge grows here (normally found only on the coast of Lake Baikal in Siberia).