Question: When did the Army arsenal formerly located on the site now occupied by the Midewin National Tallgrass Prairie open?
Sentence (from "Midewin National Tallgrass Prairie"): The first national tallgrass prairie ever designated in the U.S. and the largest conservation site in the Chicago Wilderness region, it is located on the site of the former Joliet Army Ammunition Plant between the towns of Elwood, Manhattan and Wilmington in northeastern Illinois.
Relevant evidence: Yes