An afternoon lightning strike is to blame for the blaze that brought down the 10,000-foot lookout tower, which was built in 1931 and renovated in 1998.  

“The building was eligible for inclusion on the National Register of Historic Places, both for its significance in early park resource protection efforts, and as an outstanding example of the rustic architectural style that typified early park architecture,” Yellowstone National Park Deputy Superintendent Pat Kenney in a statement. “We are disappointed that this historic structure, as a window into the past, is gone.”