The sedimentological properties of samples collected from exposures in wadi floors are reported. These studies emphasise the natural variability of erosional and depositional processes in this environment. Some of the sedimentological changes observed appear to be of archaeological significance. They indicate that in the recent geological past, either increased flooding occurring as a result of natural environmental fluctuations, or irrigation practice, has caused the elevation of saline groundwaters in the wadi floor sediments to levels which might have had deleterious effects on the contemporary agricultural system. Sites at the margins of the wadis are more sensitive to such changes than those more centrally located on the wadi floor. No evidence for significant climatic change at the times of the extensive Romano-Libyan occupation of the pre-desert region has been detected. There is, however, evidence of much wetter periods in the more distant past, which have left a legacy of mature soils on the basalt plateaus, which may have been extensively used in the Romano-Libyan period.