Organic and inorganic forms of carbon in the soil are the second and third largest pools in the world. Arid and semiarid rangeland soils contain most of the inorganic carbon. The determination of organic and inorganic carbon fluxes from soils is important in understanding the global carbon budget. The isotopic signatures of organic and inorganic carbon are different. A procedure was developed to separate the soil fluxes into organic and inorganic sources based on their isotopic signatures. Soil carbon dioxide flux samples were collected for two years at two rangeland sites with varying soil carbonates. Results indicate that the high carbonate soil had a dominate flux from the soil inorganics. The lower soil carbonate site fluxes were predominately organic. Summer rains stimulating microbial activity and extended dry periods caused shifts and reversals in the organic and inorganic carbon fluxes. The finding that inorganic soil carbon fluxes can be dominate for most of the year calls attention to the importance of rangeland soils in the world’s carbon budget.