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The Hsanda Gol Formation is a geological formation dating from the Oligocene, located in Central Mongolia in the Tsagan Nor basin. The fossilised animals are mostly Middle Oligocene mammals, with an abundance of rodents.
Geology
The 2600 feet thick Hsanda Gol formation is covered in various places by Miocene-age variegated clays, sands, and gravels. It rests on top of the Early Cretaceous Hühteeg Svita formation. The lower portions of the formation are composed of yellow conglomerate, with the higher areas being dominated by red clays, silts and sands, as well as lava and basalt flows.
During the Oligocene, the area is believed to have been a sparse plain with few wooded areas, due to the absence of large herbivores (with the exception of Paraceratherium, which is known from the formation).