*Four habitat types were sampled: 1)playa, within a dense stand of large (3-5m tall) mesquite growing along the edge of a large playa; 2) arroyo, with widely spaced mesquite trees (3-5m tall) along the margin of temporary water courses; 3) dunes, which are dominated by low-growing coppice mesquite; the dunes vary in height from 1.5 to 4 m above the interdune soil, which forms a layer 10-20 cm thick over an indurated CaCO3 (caliche) layer through which roots of mesquite penetrate; and 4) grassland, at the base of a watershed with widely scattered mesquite, 2-3 m tall, many of the plants being multiple-stemmed.