TYRONE TOWNSHIP, Mich. (WOOD) — Mystery solved: The bunker-like area found in a state game area in Michigan was built by teenagers, officials say.

The Michigan Department of Natural Resources said that after Nexstar’s WOOD-TV aired a report on the bunker in the Rogue River State Game Area Monday, a mother called the Kent County Sheriff’s Department.

She said her 15-year-old son and his friend built the bunker for fun.

Located about a mile hike into the state game area northeast of Kent City and about 50 yards off a narrow trail, the bunker is about 15 by 15 feet and almost 3 feet deep.

On Monday, about 70 sandbags were stacked around the perimeter and several more were sitting in the corner. There were some freshly cut down trees nearby.

Cutting down trees, digging large holes and leaving sandbags on state land is illegal, the DNR said. A conservation officer will meet with the boys and make them fill the hole and restore the area.

No charges are expected, the DNR said.