Nebraska’s Runningwater Formation preserves fossils from the Hemingfordian stage of the Early Miocene within the Neogene. Composed chiefly of sandstones and conglomerates deposited by ancient river systems, it records a fluvial landscape rather than marine or lake environments. The formation is especially important for its fossil mammals, and it has also produced reptiles such as Macrochelys schmidti, Rhineura marslandensis, and Sceloporus. Together, these remains help illuminate Nebraska’s prehistoric landscapes and the animals that inhabited them during the Early Miocene.