Sand extraction from coastal sand dunes results in significant loss of sand from the natural system, destruction of dune vegetation and dramatic geo-technical modification. This can place significant limitations on land use. The identification of, and extraction from sand bodies that are not part of active coastal barriers or dune structures is therefore considered to be a more environmentally sound practice . Sedimentological investigation of several back-barrier estuarine sequences have located several marine sand deposits within the Illawarra region that meet the above criteria. The action of overwash, possibly by tsunami waves in the late Holocene has deposited large volumes of sand from coastal barrier systems into their respective back-barrier environments. Several of these deposits are identified and mapped with detailed data on one of the deposits presented in this paper. These sand deposits are dominated by fine- to medium-grained quartz sand and hence represent a potential resource for construction sand in particular sand for concrete production. Advances in the understanding of late Holocene overwash activity on coastal sediments could assist in the identification of other sand deposits removed from the coastal zone. Such deposits may allow sand mining activities, providing significant resources of fine- to -medium-grained sand for the construction industry and beach nourishment programs under the principles of sound environmental management.