A kid brontosaurus embarks on a journey to find the mythical Great Valley in this animated film set in the Prehistoric Age. It was a time when dinosaurs ruled the Earth, but the environment did not provide adequate vegetation for the peaceful plant-eaters. Many brontosauruses, including the parents of young Littlefoot, talk of a valley full of "tree stars" or leafy greens. But when a natural disaster leaves Littlefoot orphaned, he sets out to find the special place, gaining friends and dodging a ferocious T-Rex in his travels.