Forty two samples were selected from the Kellogg Soil Survey Laboratory (KSSL) archive. The soils (41) were taken from the A horizon except for one sample that came from an O horizon. The samples represented 9 of the 12 US soil Orders, including Mollisols (23), Alfisols (5), Ultisols (5), Andisols (2), Entisols (2), Inceptisols (2), Aridisols (1), Histosols (1) and Vertisols (1). The soils varied widely in SOC (3.0 – 288.4 g kg-1; mean 31 g kg-1), pH (4.3 – 8.5; mean 6.2) and clay content (3.6 – 47.0%; mean 21.5%) The geographic origin of the selected samples and the distribution of SOC concentrations, clay contents and pH values are in the sample selected materials.