The central theme of these studies involves the linkage between weathering intensity and the resulting products in ancient soil profiles. This project proposes to extend this methodology to coarse-grained clastic rocks of the Chinle Formation at Petrified Forest National Park (PEFO). The research hypothesis for this study focuses on the effects of meteoric diagenesis on feldspars and rock fragment, and the weathering production of clay minerals as a guide to constraining climate change during Late Triassic in the sandstones at PEFO. This hypothesis will be tested by detailed investigation of Chinle Sandstones and the comparison of these results with paleoclimate data determined from paleosols. To address the above research hypothesis, this investigation will utilize two methods: 1.) petrographic and SEM observations of grain types and cement textures and 2.) clay mineral identification using X-ray diffraction. I will use these data to identify general trends in Chinle sandstone characteristics through the stratigraphic section to assist with climate interpretations. Thin sections will be petrographically assessed and point-counted for the recognition of any change in sedimentation source area as well as abundance and types of cements. It is assumed that: 1) Increasing rainfall and temperature leads to increased destruction of feldspars and rock fragments and 2) Increasing rainfall and temperature leads to the formation of a continuum of clay mineralogy spanning semectitic to kaolinitic clays.