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In northwest Florida plinthitic soils commonly form adjacent to well-drained, nonplinthitic soils on the same landform. Differences in these soils are related primarily to natural drainage. The hypothesis that a lithological discontinuity occurred below the plinthic horizon in the plinthitic soils was proposed and tested: strata below the discontinuity impeded drainage through the soils, causing plinthite to form. Properties of three plinthitic soils and one nonplinthitic soil from the East Pittman Creek watershed were compared to test this hypothesis. Pedologically significant differences in morphology (e.g. consistence, color, and texture), clay-free silt content, and fine sand content as a percentage of total sand content were observed between plinthic and 2C horizons and between the plinthitic and nonplinthitic soils. Three distinct strata were identified using the principle of random association. Anomalously high clay, iron, and phosphorus contents in the horizons above the 2C horizons and the laminar ironstone at the boundary between the Btv and 2C horizons indicated that the lower stratum impeded water movement. In conclusion, a pedologically significant lithological discontinuity does exist in the soils in East Pittman Creek watershed. Contribution of the Inst. of Food and Agricultural Sciences, Univ. of Florida, Florida Agric. Exp. Stn. Journal no. 7636.