Landscape position, grazing, and seasonal variation in precipitation and temperature create spatial and temporal variability in soil processes, plant biomass and composition in grasslands. However, it is unclear how this variation in plant and soil properties affects mineral soil carbon (C) turnover rates. The aim of this study was to explore the effect of grazing, topographic position and seasonal variation in soil moisture and temperature on decomposition rates of standard material (cotton cloth). Cotton cloth turnover rates (0 – 10 cm), and soil properties (soil moisture, soil temperature, soil C and N concentration) were measured at monthly intervals inside and outside long-term ungulate exclosures in hill-top (dry) to slope bottom (mesic) grassland throughout the 2004 growing season in Yellowstone National Park. There was no difference in cotton cloth turnover rates between the grazed and ungrazed sites, which indicates that grazers do not affect decomposition of standard material in the ecosystem studied. The spatial variability in decomposition was positively related to soil moisture, and negatively to soil temperature. Thus, with increasing soil temperature, decomposition rates decreased.