This location is due west of abandoned mine shaft 1, at the end of the southwest spur off 84. It is one of the most southwestern locations on the map.
There's a weapons workbench outside of the concrete control and maintenance building. The small building has minor loot and a locked room with a duffel bag and a mattress. Out west is a small derelict encampment with an old trailer and a Grafton Steal truck, while directly south is a cult sacrificial altar.
Hornwright testing site 2 appears only in Fallout 76.