Technical Abstract: The ability to inventory soil C on landscapes is limited by the ability to rapidly measure soil C. Diffuse reflectance spectroscopic analysis in the near-infrared (NIR, 400-2500 nm) and mid-infrared (MIR, 2500-25000 nm) regions provides means for measurement of soil C. To assess the utility of spectroscopy for soil C analysis we compared the ability to obtain information from these spectral regions to quantify total, organic, and inorganic C in samples representing 14 soil series collected over a large region in the west central US. The soils temperature regimes ranged from thermic to frigid and the soil moisture regimes from udic to aridic. The soil ranged considerably in organic (0.23 - 98 g C/kg) and inorganic C content (0.0 to 65.4 g carbonate C/kg). These soil samples were analyzed with and without an acid treatment for removal of carbonate. Both spectral regions contained subastantial information on organic and inorganic C in soils studied and MIR analysis substantially outperformed NIR. The ability of MIR spectroscopy to quantify C in diverse soils collected over a large geographic region indicated that regional calibrations are feasible.