undifferentiated rock units

Paleontology and geology

An episode of mountain building (the Nevadan Orogeny) occurred in southwestern Arizona during the Jurassic. The mountain building and associated volcanism dumped huge amounts of sediment into low-lying areas to the north. Most of northern Arizona was an interior lowland during the Jurassic, variously dominated by rivers and wind-sculpted landscapes with spectacular dune fields. This map indicates the presence of Jurassic rocks scattered throughout the higher elevations in the state.