Almost all the mammal fossils found in Kentucky are from the Quaternary. Quaternary clays, sands, and gravels are found in valley bottoms and terraces all over Kentucky. The most famous site for Quaternary mammal fossils is Big Bone Lick, which is now Big Bone Lick State Park near the Ohio River in northern Kentucky. The first paleontological site in North America was probably at Big Bone Lick. A French commander organized a dig there in 1739. Bones retrieved by him were sent to the Natural History Museum in Paris, France. Later, Thomas Jefferson sent Captain William Clark, of Lewis and Clark fame, to dig the bones there in 1807. Jefferson sent these bones to the American Philosophical Society in Philadelphia (and he kept some of them at the White House, and later at Monticello, his home). Much later, in the 1960's, the University of Nebraska conducted a dig at Big Bone Lick. The following mammal fossils have been recovered at Big Bone Lick: possible wolf, possible black bear, modern bison, ancient bison, two types of musk ox, American moose, wapiti elk, common Virginia deer, extinct stag moose, caribou, flat-headed peccary, extinct North American horse, possible tapir, American mastodon, woolly mammoth, and two types of giant ground sloth. The most common fossil found at Big Bone Lick was the modern bison.

The herbivores (plant-eating animals) were attracted to Big Bone Lick because of salt springs. The big mammals tramping through the water-laden, clayey deposits created a deep, sticky mire, which trapped all sorts of salt-starved mammals who came to lick the salt. Bones are generally not articulated because subsequent trampling long after death caused the bones to be spread apart.