Triassic-Early Jurassic sedimentation is eastern North American rift basins and the contemporaneous but tectonically quite different ancient alluvial plain of the Colorado Plateau responded in similar ways to changing levels of atmospheric carbon dioxide (pCO₂). High pCO₂ coincided with, dramatic and periodic lake level cycles in the rifts and highly erratic river deposits in both areas. In the rifts, low pCO₂ saw lakes fluctuate much less and their sediment cycles become even more regular, while rivers deposits became monotonous. On the Colorado Plateau, however, low pCO₂ was associated with the most regular, cyclic sediment cycles, as rivers became less extreme and the system grew more sensitive to changes in soil formation, dust, and precipitation. Thus, the intensity of extreme climatic events, driven by CO₂ levels, controlled the major features of the rock record in both areas, regardless of their tectonic setting. New continuous cores and new dates from the Colorado Plateau are needed to confirm these patterns and their links to ancient atmospheric CO₂ and climate cycles.