A midden is essentially a prehistoric rubbish deposit, an accumulation of shells, animal bones, charcoal, and discarded domestic material left behind by communities who lived, ate, and worked in a place over long periods of time. They are among the most informative deposits an archaeologist can encounter, precisely because they are the unguarded, everyday leavings of ordinary life rather than the deliberate constructions of monument-builders.

Sligo's coastline and its immediate hinterland have long been associated with early settlement, and shell middens in the west of Ireland frequently date to the Mesolithic or Neolithic periods, though they continued to accumulate through the Bronze Age and beyond. The presence of one at Culleenduff suggests the locality was used, perhaps repeatedly, by people with access to coastal or estuarine food sources. Beyond its existence as a recorded monument, the specific details of this particular deposit remain to be fully documented in publicly available form.