Camp Elliot, adjacent to MCAS Miramar had multiple live fire ranges during WW-II. And for many years since, unexploded ordnance continued to turn up. In fact, in 1983 in a new residential community built upon an old range, two 8-year-old boys were killed when they came across a 37mm unexploded shell.
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Ft Knox is the same way. Your not even allowed to attempt any kind of digging out there with out a whole bunch of paperwork. They had to shut down the CIF when a nearby excevation site uncovered a couple of old artillery fired gas shells. And somebody had found a 105 shell the same week digging a hole in his backyard in base housing.