The post-Cambrian and pre-Upper Devonian Shoo Fly Complex 1s interpreted to contain the remnants of an early to middle Paleozoic subduction system. It contains the Culbertson Lake allochthon, which inturn includes the sandstone and mudstone dominated Poison Canyon and Red Hill units. Quartz-rich (>80% Q) sandstone samples from the Poison Canyon and the Red Hill units were collected and point counted by previous investigators. This and other work indicated that sand-sized detritus within the Shoo Fly Complex was derived from a transitional to continental interior provenance. In order to assess whether or not the chemically-based provenance discrimination model yields results which are internally consistent with the more conventional QFL or petrologically-based discrimination model, 21 mudstone samples were collected and analyzed for major, trace and rare earth elements (REE). Samples from both the Poison Canyon and Red Hill units have Al2°-3/Ti()z values ranging between ~ 18 and ~24, mean Th/U values that are greater than 3.8, and REE patterns characterized by LREE enrichment, negative Eu anomalies, and slightly fractionated HREE patterns. These results are consistent with a source region dominated by old upper continental crust. Thus, the results of this study indicate that both the chemically- and petrologically-based proven ancediscrimination models yield similar interpretations for the source of siliciclastic detritus in the Poison Canyon and Red Hill units. Such a conclusion strengthens the belief that both models generally produce reliable results. However, more work focused on identifying the similarities and dissimilarities in source-rock interpretation produced by the two provenance-discrimination models is clearly needed. Our work has just begun.