The sub-Cretaceous unconformity in New Mexico
— Steven M. Cather

Except locally in the Bisbee basin of southwestern New Mexico, the base of the Cretaceous System in New Mexico is an unconformity. Within the Bisbee basin, the base of the Cretaceous overlies Jurassic, Paleozoic, and Proterozoic rocks in the complex floor of the basin and along its margins. The broad (~500 km wide) region north of the backarc Bisbee basin and related Chihuahua trough was uplifted, tilted slightly north, and erosionally beveled as the basin developed during the Late Jurassic–Early Cretaceous. In eastern New Mexico, this beveled region was subsequently onlapped and buried by upper Albian marine, deltaic and fluvial deposits related to the late Early Cretaceous Kiowa–Skull Creek transgression of the Western Interior Seaway. There, upper Albian beds overstep progressively older rocks to the south (ranging from Upper Jurassic in northeastern New Mexico to Permian in south-central New Mexico), resulting in a southward-increasing, pre-Cretaceous lacuna. The subsequent, more extensive Greenhorn transgression (Cenomanian, early Late Cretaceous) produced an analogous southward-increasing lacuna on what is now the southern Colorado Plateau, where the Dakota Sandstone oversteps rocks ranging from the Lower Cretaceous Burro Canyon Formation in northwestern New Mexico to Permian and possibly Proterozoic rocks near Silver City.