Drill core from samphire and mangrove marshes north of Gillman - Wingfield are used to interpret the shallow sub-surface stratigraphy of the region. A Holocene marine sequence up to 8 metres thick overlies Late Pleistocene alluvial (Pooraka Formation) and coastal marine (Glanville Formation) sediments. The Holocene strata are saturated, loose, organic-rich and permeable, with very low bearing capacity. The underlying Glanville Formation is variably cemented, including a surficial hardpan, but is also loose and friable in parts. The marine strata are underlain by 70 metres of stiff and largely impermeable alluvial clays (Hindmarsh Clay) that have superior bearing capacities.