The Warm Springs soil series which contained variable amounts of subsoil available (sodium bicarbonate extractable) phosphorus was studied to explain the variability and distribution of the NaHCO3-P in the subsoil. Four pedons ranging in subsoil NaHCO3-P from less than 10 ppm to greater than 30 ppm were selected in an area of less than 200 ha located on a nearly level, low lake terrace east of the Great Salt Lake in Weber County, Utah. The morphology of each pedon was described in the field and samples collected from each genetic horizon or contrasting layer. Each soil sample was analyzed for total phosphorus, NaHCO3-P, water- soluble phosphorus, pH, extractable iron , calcium carbonate equivalent, electrical conductivity and water-soluble sodium. Four horizons were selected from each pedon for anal ysis of parti cle-size distribution, clay-size carbonate and non-carbonate clay. The very fine sand fraction of four horizons from two of the pedons were studied petrographically to determine the amount of apatite present. Thin strata with higher chroma were separated from adjacent layers and analyzed for extractable iron and NaHCO3-P. Cicada casts and their surrounding matrix were separated and analyzed Selected soil samples were shaken with sodiumphosphate solutions and then analyzed for NaHCO3-P to determine the influence of the amount of phosphorus in solution on the amount of phosphorus extracted. NaHCO3-P below the calcic horizons was highly variable, 10 ppm or less in two pedons and up to 40 ppm in the other two. Subsoil horizons with pH values greater than 10.0 and relatively large amounts of water-soluble sodium contained more than 10 ppm NaHCO3-P. Extractable iron and NaHC03-P were concentrated in subsoil strata with higher chroma. The results indicated that large amounts of NaHCO3-P in the subsoil were primarily due to the presence of readily soluble sodium phosphate. Weathering of apatite in the surface horizons did not contribute the NaHCO3-P below the calcic horizons. The most likely source of NaHCO3-P in the Warm Springs subsoil , however, was the sediments deposited in the low lake terraces and river flood plains by the Weber and Bear Rivers. Lateral flow and vertical fluctuations of the water table were suggested as a means by which the NaHCO3-P could be extracted from some areas and concentrated in others. Although certain soil properties might indicate the probable occurrence of more than 10 ppm NaHCO3-P in the subsoil, this study did not provide a method for identifying all subsoils with appreciable amounts of NaHCO3-P.