A three-story observation tower dedicated to the nation's first president is closed for inspection after it was struck by lightning at Washington Monument State Park in western Maryland.

The Department of Natural Resources said Friday that three people who had taken shelter in the structure were blown out of the doorway by the lightning strike Thursday afternoon. Two refused treatment and one was taken to a Hagerstown hospital with a head injury that authorities said was not life-threatening.

Natural Resources Police spokeswoman Candy Thomson says the approximately 30-foot structure atop South Mountain near Boonsboro doesn't appear to have sustained major damage, but officials want to make sure it's safe.

The stone tower has an internal staircase leading to an observation platform. The original tower was dedicated in 1827.