The miogeosyncline in southeastern Idaho subsided slowly and filled with about 50,000 feet of Paleozoic and Mesozoic sediments, whereas the adjacent Wyoming shelf remained relatively positive. During the development of the overthrust belt, Early Cretaceous to early Tertiary, the area of the miogeosyncline was uplifted at least 50,000 feet and more than 20,000 feet of Cretaceous sediment, derived from the rising highlands, accumulated in a foredeep basin in western Wyoming. The rising lands were progressively overthrust on the subsiding area. After overthrusting, the area of the foredeep basin rose more than one mile and the area of the highlands subsided an unknown amount. Isostatic interpretations indicate that the latest phase of opposed vertical movements is still active. These recent vertical movements generally have reversed the dip directions of the major thrust surfaces from east to west.