Complex sentence: During the Cretaceous Period, along the western shore of the Western Interior Seaway there was active volcanism and foreland subsidence brought about by the Sevier orogeny, formed by the convergence of the oceanic Farallon and Kula Plates with the North American Plate.
Split into simpler sentences: During the Cretaceous Period, along the western shore of the Western Interior Seaway there was active volcanism and foreland subsidence brought about by the Sevier Orogeny. The Sevier Orogeny formed by the convergence of the oceanic Farallon and Kula Plates with the North American Plate.