LEELANAU COUNTY, MI – Authorities are investigating after someone triggered a bomb that destroyed the restroom at School Lake boat launch in the Sleeping Bear Dunes National Lakeshore.

Police estimated damages at $14,000.

The boat launch, on National Park Service property, has re-opened.

A resident called 911 at 4:29 a.m. Sunday, Oct. 20, after hearing a large explosion that shook his house. He was sure it was not lightning.

He searched the area, but could not find what caused the explosion. Leelanau County sheriff’s deputies also could not find where the explosion occurred.

Later in the day, dispatchers got a call that the restroom at the boat launch was severely damaged. National Park Service workers determined that the structure appeared to have been blown up. They secured the scene until a state police bomb squad and FBI arrived on Monday morning.

The resident who called 911 to report the sound of an explosion lives two miles away from the boat launch.

Police said the bomb had been placed in or next to the structure. Police withheld additional details of the investigation.

The National Park Service is investigating the incident. Anyone with information is asked to call the National Park Service at 231-326-5135 or the Leelanau County Sheriff's Department at 231-256-8800 or the Confidential Tipline at 231-256-8696. Email information should be sent to tips@co.leelanau.mi.us.

John Agar covers crime for MLive/Grand Rapids Press E-mail John Agar: jagar@mlive.com and follow him on Twitter at twitter.com/ReporterJAgar