More than 100 groups of mammals have been found in the Miocene (37 – 20 mya) John Day Formation near Kimberly, Oregon. I'm planning a field trip this July to collect in the fossiliferous strata that have yielded beautifully preserved speciments of many of the animals we see domesticated today.
Dogs, cats, swine and horses are common. Oreodonts, camels, rhinoceras and rodents have also been found in this ancient deciduous forested area.