Sinclair City is the name given to the land discovered by Earl Sinclair in the third season Dinosaurs episode "The Discovery." A lush forest paradise inhabited only by the indigenous cavemen, this land is accidentally found by Earl during WESAYSO's annual golf tournament. "Sinclair City" is the name suggested by B.P. Richfield, as WESAYSO begins development of an urban metropolis on the land.
Under pressure from Robbie Sinclair (as well as tax assessor Walter Sternhagen), Earl returns the land to the cavemen. Their ownership is short-lived, however, as the government of Pangaea bilks them, sending the cavemen to reservations. Still, the nation honors those "lovable fuzzballs" through a new baseball stadium, built on the land, to be the home of the newly formed team "The Central Pangaean Cavemen."