Sediment filled the subsiding Furnace Creek Basin as the area was pulled apart by Basin and Range extension. The resulting -thick Furnace Creek Formation is made of lakebed sediments that consist of saline muds, gravels from nearby mountains and ash from the then-active Black Mountain volcanic field. Boron, which is abundant in this formation, is dissolved by ground water and flows out onto the northern end of the Death Valley playa. Today this formation is most-prominently exposed in the badlands at Zabriskie Point. Additional subsidence of the Furnace Creek Basin was filled by the four-million-year-old Funeral Formation, which consists of of conglomerates, sand, mud and volcanic material. Another smaller basin to the south was filled by the Copper Canyon Formation around the same time. Footprints and fossils of camels, horses, and mammoths are in all three of these Pliocene formations.