Paleoecological and paleoenvironmental interpretations of stable isotope composition of pedogenic carbonate collected from the Pliocene-early Pleistocene St. David Formation in southeastern Arizona, United States, correlate with other proxy records of paleoclimate in the western United States. Wetter, and perhaps cooler, conditions between 3.2 and 2.8 Ma are associated with lacustrine highstands at Tulelake and Searles Lake in California. A general trend toward drier conditions in the late Pliocene is also apparent in all records. A protracted arid, monsoonal climate in the early Pleistocene, implied by the soil isotope data from Arizona, is not as readily correlated to other climate records and is perhaps related to uplift in the southern Cordillera. Soil-carbonate isotope data provide relatively continuous paleoclimatic records from fluvial sequences that supplement lacustrine records. Together they provide a framework for interpreting Pliocene climate.