The early Paleozoic of northwestern and west-central Colorado is represented by continental shelf and continental shelf marginal sedimentary rocks of Late Cambrian, Ordovician, and Late Devonian ages. Differentially epeirogenic movements along fracture systems having Precambrian origins affected sedimentation patterns and probably mostly account for intervening times of erosion or nondeposition; activity along these tectonic elements persisted into the Neogene and possibly continues. These tectonic elements are west-north-west, south-southeast, and northeast trending fracture systems and an east-trending aulacogen in the approximate area of the modern Uinta Mountains. North-central Colorado was emergent land throughout most of this time and shed clastic sediments at varying rates to the west and southwest. Episodic continental motion and the effects of the Antler orogeny to the west are probably the direct causes of these epeirogenic movements.