DiMA's cache is a small island just northwest of Rayburn Point on the western edge of the map. It is where DiMA buried the kill switch for the Island's wind farm, which must be retrieved for the quest Cleansing the Land. A mound of "disturbed earth" can be activated, unearthing a toolcase containing the kill switch code.
Although there are usually no monsters on the island itself, the area surrounding it is guarded by anglers. There is also a rare chance for a mirelurk queen to spawn in the vicinity.
There is an island a short way north of DiMA's cache which is just barely considered to be outside the map boundary. Two mirelurk queens can spawn there.