BLUFFTON (AP) - State and federal authorities are investigating an explosion last month of a stream gauge building along the Upper Iowa River in northeast Iowa.

Kaylene Carney, a U.S. Geological Survey spokeswoman, says no information was made public about the explosion when it occurred.

The Winneshiek County sheriff's office says the Sept. 19 explosion destroyed the building, which is about 12 miles northeast of Decorah. No one was injured.

Officials say the explosion caused about $20,000 in damage to the building.

No other information was immediately released.