Abstract Chronostratigraphic correlations of the mostly nonmarine and transitional-marine rocks of Late Jurassic and Early Cretaceous age in central Wyoming recently published by May and others (in press) and Meyers and others (1992) are extended into northeastern Wyoming and Montana on the basis of widely recognizable time-marker beds. These new regional correlations provide additional evidence that lower Cretaceous alluvial sandstone bodies are not confined to a relatively thin stratigraphic interval. Instead, they appear to be oldest in the proximal part of the Rocky Mountain foreland basin and to systematically decrease in age toward the medial and distal parts of the basin.