The upper diluvial boundary is difficult to determine in some areas, such as the Arctic coast of North America and the fossil locations of Australian marsupials. An even more difficult area is the top layers of sedimentary rocks of the southern and central High Plains where numerous mammal and other fossils are buried. Despite evidence of a post-Flood paleoenvironment of Agate Fossil Beds National Monument and Ashfall Fossil Beds State Historic Park, they likely are within the Ogallala Group (two or more formations). The Ogallala Group is widespread and thin and was spread hundreds of kilometers east. About half of its top was subsequently eroded. Quartzite rocks from the Rocky Mountains are marked with percussion marks indicating torrential flow. Some quartzite cobbles and boulders have spread 800 km from their source in the southern Rocky Mountains and are found on valley interfluves in central Texas. Most of the fossils in the Group are of animals not living today or during the Ice Age. It is difficult to explain how many millions of animals were buried in the southern and central High Plains with a post-Flood scenario. It is easier to explain that the animals were buried during the Genesis Flood. The apparent post-Flood features can be explained by the BEDS Model. Grass seed fossils associated with a rhino could be because grass fossils are very abundant in the Ogallala Formation.