Arid systems represent an important component of the global soil carbon (C) budget in that they cover twelve percent of global land area and contain nearly thirty five percent of global soil C stocks, both organic (SOC) and inorganic (SIC). The objectives of this study were to quantify SOC and SIC stocks in Arizona biomes, using Arizona as a model system for arid lands. Biome distribution was extracted from the Arizona GAP dataset, while soil C data were extracted from the Arizona State Soil Geographic Dataset (STATSGO) at a scale of 1:250,000, and the western Yavapai County Soil Survey Geographic Dataset (SSURGO) at a scale of 1:24,000. Soil data were converted to a raster format and a raster based method used to estimate SOC and SIC stocks by biome. Statewide, STATSGO soil C stocks indicate Arizona contains 0.5 and 1.5 Pg of SOC and SIC, respectively, with 27% of the SOC in pinyon-juniper biomes, and 34% of SIC in creosotebush-bursage biomes. A comparison of soil C estimates indicates significantly greater estimates of biome SOC and SIC using SSURGO data relative to STATSGO data. SSURGO soil C estimates vary considerably between the raster based and soil taxa based methods of data aggregation. Soil taxa data exhibited large intra-unit variation in each biome. In addition, soil C varied substantially within a soil taxa unit between biomes (e.g., Haplargid SOC of 4.0 and 13.5 kg m-2 in the paloverde-cacti and montane pine forest biomes, respectively). Raster based soil C estimations incorporate the spatial distribution and areal land cover of each soil type within a biome, providing a more accurate representation of soil C stocks.