Among the most unusual features of the forest are the sinkhole lakes in its center. These represent erosions in the limestone floor of the forest. One of them is Section 4 Lake (pictured here), incidentally one of the most beautiful of the group, with a wonderful aqua-marine color. These lakes are part of a cave formation, cone-shaped, three to four acres in diameter at the surface, with depths from 30 to 60 feet.

The lakes were formed by surface cavities. Such cavities outcrop in Presque Isle and Alpena counties and are called Michigan caves. Evidence of the formation of the lakes occurred on Section 4 Lake during the winter of 1950-51, when the west end caved in, pulling in trees with it, including a red pine 150 years old. A large log on end that was pulled down by the suction during this cave-in is still visible.

~ Sibley Hoobler in Pigeon River Country by Dale Clarke Franz