The arid period of Salado Salt evaporation changed slightly as the dolomites and anhydrites of the Rustler Dolomite were laid down in the last drying moments (geologically speaking) of the Permian. Then as the seas retreated to the south, the fine-grained red sands and silts of the Dewey Lake Redbeds were spread as a thin blanket over the low lands basking under the hot Permian sun. This was a time of dying; whole races of vertebrate and invertebrate animals were wiped out, to be known today only from their fossil remains. As the dim unmarked episode of latest Permian time merged into the Triassic, an inkling of coming life was recorded in the rocks. The amphibians were more modern types, and they gave rise to the most striking of early land animals, the reptiles. This was the beginning of the conquest of the land by the reptiles, which culminated later in the dinosaurs, and was aided by the retreat of shallow seas from the continents, a change survived chiefly by the species adapted to living on land. MESOZOIC ERA The Mesozoic Era dawned in New Mexico on extensive plains, except for a northwest-trending range in the extreme north-central part of the state. During this, the early part of the Triassic Period (180 to 230 m.y. ago), sands and muds eroded from New Mexico were carried westward to northeastern Arizona where they now form the Moenkopi Formation, the brilliant reds and purples of the Painted Desert region. Uplands arose in late Triassic time in southwestern New Mexico. Along with mountains in south-central Colorado, these highlands were torn apart by water and wind, and the detritus was swept into sheets of brightly colored sand and shale. These beds are thickest (about 2000 feet) along the New Mexico—Texas line east of Roswell and in west-central New Mexico (near Grants) extending westward into northeastern Arizona. The eastern Triassic rocks are the redbeds of the Dockum Group with the lower Santa Rosa Sandstone and the upper Chinle beds. The northwestern rocks are the Chinle Formation overlain by the redbeds of the Wingate Sandstone.