|The seaway was at its maximum extent during this stage. Warm-water conditions, spreading to the U.S.-Canadian border, were ideal for deposition of limestones. Mountains continued to be uplifted and volcanoes were active, particularly in the region that would become the Sierra Nevada mountain range in California. Evidence for volcanism is seen today as layers of volcanic ash in rocks that represent slow sediment accumulation, such as coal and deep-water shale. Continued erosion of the mountains provided more fine-grained sediments to the coastal plain allowing the shoreline to prograde eastward, especially in a broad belt extending from southern Utah into New Mexico. Thick peats accumulated close to the shoreline in areas of year-round precipitation and later formed thick coal beds of potential economic value in the Ferron Sandstone of Utah. On the east side of the seaway, evidence for peat accumulation is absent because erosion has removed terrestrial rocks of Late Cretaceous age.|
*See Roberts, L.N.R., and Kirschbaum, M.A., 1995, Paleogeography of the Late
Cretaceous of the Western Interior of middle North America-- Coal
distribution and sediment accumulation: U.S. Geological Survey Professional
Paper 1561, 115 p., (1 pl.).