Soil depth effects on honey mesquite (Prosopis glandulosa Torr) cover and density and perennial grass standing crop were evaluated over an 11-yr period (1995–2005) on two lightly stocked and two conservatively stocked pastures on the Chihuahuan Desert Rangeland Research Center in south-central New Mexico. These four adjoining pastures have similar size, vegetation, and soils. Soils in these study pastures are primarily light sandy loams varying from a few centimeters to 1 m or more in depth underlain by a calcium carbonate layer. Deep soils had lower perennial grass standing crop and higher honey mesquite cover and density than did shallow soils at both the beginning (1995–1997) and ending (2003–2005) periods of study. Average perennial grass standing crop across the four study pastures dropped 82% between 1995–1997 and 2003–2005 because of drought during the last 5 yr of study. Honey mesquite canopy cover and perennial grass standing crop did not differ between light and conservative grazing treatments at the beginning or end of our study. Honey mesquite canopy cover did not change from 1995–1997 to 2003–2005 but honey mesquite density was higher in 2003–2005 than in 1995–1997. Our study shows that both soil depth and climatic fluctuations have a major influence on vegetation dynamics in desert and semiarid areas.