It's right in Valdez.
At the far NE end of Port Valdez, 2.7 km (1.7 mi) NW of Old Valdez. Most easterly and largest island in the Mineral Creek Islands group.
Ammunition Island lies as a barrier to duck flats, and is maintained by the Port of Valdez. It's surface has been flattened to an elevation of about 12ft, and is used as a cargo shipping facility. There are three large silo's built upon it. Access to the island is regulated and while there is a bridge to it. Special security clearance and cards are need to access the island.
Not sure why it's called Ammunition Island, and most locals probably wouldn't identify it as that. But that's what it's called according to official maritime references.