R Racetrack, The 22 Rainfall 2 Rapid City, S. Dak. 20 Raton Basin 24 Raton Formation 16 Raton Mesa 20, 23 Raton section 10, 20, 23, 45 Red Hills 48, 49 Red Valley 22 Republican River 4, 29, 48 Rhinoceroses 16, 18 Rio Grande 7, 45 Rocky Mountains 5, 19 Roswell, N. Mex. 45 S Sabinal River 46 Salina, Kans. 4 Saline River 4, 48 San Antonio, Tex. 47 Sand dunes 44, 49 Sand Hills, Nebr. 29 Sangre de Cristo Mountains 7, 45, 46 Scotts Bluff National Monument 27, 42 Sedimentation 10, 11, 32 Shonkin Sag 35 Sinkholes 47, 48 Skyline Drive, Canon City, Colo. 43 Smith River 38 Smoky Hill River 4, 48 Smoky Hills 48, 49 Soil development 16 Solomon River 4, 48 Solution cavities 45, 47, 48 Sonora, Tex. 47 South Dakota 20, 29, 33, 34 South Dakota Badlands 16 South Platte River 4, 7, 42, 43, 44 Spanish Peaks 19, 24 Spruce trees 2 Stream deposition 11, 32