The susceptibility of these soils to transport by wind is clearly evidenced by the regional geomorphology--the area is dominated by soils derived from eolian dunes and from loess that is up to 75m (250 ft) thick (Busacca, 1991; Boling et al., 1998)--yet assessment of the critical source areas for P[M.sub.10] emission requires objective discrimination of both the wind erodibility and P[M.sub.10] content of eroding soils.