The youngest rocks in the county are the Tertiary rocks of the Hampshire Basin. These are characterised by the sands, gravels and clays underlying the heathland of Wareham, Studland, Poole and Bournemouth.

The coast of the Bournemouth and Poole region is made up of sandy beaches and low cliffs, with salt marshes dominating Poole and Christchurch Harbours. Bournemouth and Poole are also the most developed areas and are still growing, which increases the pressure on the fragile heathland, some of which has been designated as a National Nature Reserve, e.g. Studland Heath NNR.