Danbury, Iowa -- Officials aren't sure what caused the mysterious explosion reported by residents in three counties, but they believe it wasn't of this earth.

"The whole house shook," said Lois Vanderbur of rural Mapleton. "We thought a tree had fallen on the house."

Woodbury County Sheriff Sgt. Doug Boetger said the explosion was reported after 8 p.m. Tuesday by residents near the cities of Mapleton and Danbury as well as in Ida County.

Deputies searched for evidence of an explosion or crash, but came up empty. Their only suggestion is to look to the sky, Boetger said.

"We found nothing damaged (and) no signs of an explosion, so we're assuming it was a sonic boom by a passing jet," he said.

Airplanes flying faster than the speed of sound can cause a sonic boom.

Today, Boetger said officials don't know what kind of plane could cause a sonic boom or where such a plane would have come from.

"They didn't come from Danbury, I can tell you that," Boetger said.

Several Air Force and Air National Guard bases are scattered across the region, but none took credit for Tuesday night's noise.