IOWA CITY, Iowa (AP) – A U.S. congressional committee is seeking more information about decades of mismanagement at Effigy Mounds National Monument in northeast Iowa.

Rep. Rob Bishop, chairman of the House natural resources committee, sent a letter Tuesday to Interior Secretary Sally Jewell seeking a briefing by Sept. 9.

The Republican from Utah says it’s troubling that mismanagement went on for two decades at the monument with “little to no oversight” by the National Park Service.

Bishop’s letter comes in response to a National Park Service report that said the agency itself was “astonished” by what happened.

One superintendent oversaw an illegal $3.4 million building spree that erected a boardwalk system through sensitive American Indian burial sites. Another stole the monument’s collection of ancient human remains and hid them in his garage for decades.