the basin, whereas the Upper Cretaceous Mesaverde is a lesser contributor of oil but a significant source for gas. Ferron Sandstone coals are known to be a source of coalbed methane. The most prominent source of oil from Paleozoic rocks is the Permian Phosphoria Formation. See also Oil shale geology Roan Plateau References US Geological Survey (Mar. 2009): Nahcolite Resources of the Green River Formation, Piceance Basin, Northwestern Colorado, Fact Sheet 2009-3011, PDF file, retrieved 5 April 2009. US Geological Survey (Mar. 2009): Assessment of In-Place Oil Shale Resources, Green River Formation, Piceance Basin, Western Colorado, Fact Sheet 2009-3012, PDF file, retrieved 5 April 2009. Ronald C. Johnson and others: An Assessment of In-Place Oil Shale Resource in the Green River Formation, Piceance Basin, Colorado, US Geological Survey, retrieved 5 April 2009. Thomas, Judith C. Overview of Groundwater Quality in the Piceance Basin, Western Colorado, 1946-2009, US Geological Survey, retrieved 16 August 2013. External links Geologic provinces of Colorado Sedimentary basins of North America Oil shale formations Oil shale in the United States