Deep drainage is a potential engineering solution to dryland salinity that operates by lowering the water table and reducing the salt in the soil. By excavating drains to a depth greater than the water table, the changed hydraulic gradient allows water to flow into the drain where it can be transported to a suitable disposal site. The responsiveness of the landscape to drainage is controlled by a number of geological, hydrological and pedological factors, which are not fully understood. Evaluation of the potential benefit of drainage is based on the depth to water table, the materials that the drain will be cut into and how badly the land is affected by salinity. Various physical factors may play significant roles in determining the effectiveness of drains which is why it has proven difficult to accurately predict how much water may drain from particular areas of the landscape. Six sites within the Western Australian wheatbelt have been investigated to identify these factors. Detailed descriptions of the regolith were made at regular intervals through each drain and the regolith was sampled where appropriate in order to identify materials encountered in drains. Pedological classification and several geochemical, mineralogical and chemical analyses were carried out to group materials on the basis of common characteristics. X-ray diffraction was used to identify minerals associated with each material group and determine the potential influence of specific clay minerals on physical properties. These data were related to hydrology data in order to identify key characteristics for predicting hydrological response. An understanding of the interactions between pedology, hydrology, geochemistry and mineralogy will help maximise the utility of deep drainage and also extends our knowledge of the complex material/hydrology relationships within the regolith.