Numerous factors affect the abundance and distribution of soil microarthropods (SEASTEDT, 1984; WALLWORK et al., 1982; KAMILL et al., 1985). Few studies have separated the populations of microarthropods in litter and the mineral soil below the litter (ELKINS et al., 1982) in an attempt to examine factors affecting the species composition and numerical abundance of these organisms. Surface litter is a more exposed habitat and subject to rapid changes in water availability and thermal stresses, especially in sparsely vegetated arid environments (WHITFORD, 1986). Mineral soil is a buffered environment but provides only sparse food resources especially in arid environments........ Desert watersheds provide a number of habitats varying in soil type, vegetative cover, soil structure, soil organic matter an litter accumulations. Thus, studies of microarthropod populations on a watershed over time can provide tests of these hypotheses. Here we report the studies to test these hypotheses.