Table 4.3.

The desert zones of Fookes & Knill (1969), also see Appendix A of this book

Desert zoneDescriptionMain soil typesGeotechnical features
1. Mountain slopesMountains rising 2500 m above the central plateau; some ranges fault bounded; weathering active due to extreme temperature variations on diurnal and seasonal basis; gravity and ephemeral streams move rock fragments through zone; small fans within mountainsBare rock and angular rock debrisLikely sources of good crushed rock aggregates; mass movement hazards
2. Apron or BajadaFormed by the interfingering of rock and alluvial fans that extend around all mountains; may extend 3–5 km beyond mountainsMixtures of angular–subangular clastic debris of sand, gravel, up to cobbles and boulders. Good to poor stratification generally getting finer away from the mountainsGood for foundations and fill; flood flow and debris flow hazards
3. ‘Semi-desert’Most widespread of the zones and may extend across whole intermontane basin to the opposite side. Low slope angles and material transported by intermittent stream flows and sheet floodsSilty gravelly and sandy desert; some evaporitesGenerally very good foundation and fill material; some saline deposits
4. Central desertWind-blown material dominates, and playas and salinas occur. Very flat overall but slopes on dunes may be high locallySand dunes, loess and evaporatesLoad-bearing erratic; migrating dunes; metastable loess; aggressive saline soils; absence of coarse material