The Blackhawk Ranch fossil quarry lies south of Rock City on the lower slopes of Mount Diablo. During the Late Miocene, about 9–10 million years ago, this region was a rolling lowland and provided the first evidence that land around Mount Diablo had emerged after a long period beneath the ocean. Streamside forests of sycamore, elm, poplar, and willow supported animals such as Gomphotherium, a relative of the elephant, along with cranes, peccaries, and beavers. Fossil evidence also shows herbivores including several kinds of horses, camels, rhinos, and pronghorns that probably favored open grasslands, as well as carnivorous sabre-toothed cats, a fox, and a very large hyena-like dog that may have preyed upon them. Excavation and analysis of the fossil concentration at Blackhawk Ranch Quarry have revealed this ancient landscape and the plants and animals that lived there, and scientists from the University of California Museum of Paleontology have studied the fossils and the Late Miocene non-marine rocks there since its discovery in 1926. Geological and paleontological evidence from this ancient ecosystem remains hidden beneath the grassy slopes on the south side of the mountain.