The Great Wall is a wall that separates the Mysterious Beyond and the Great Valley. It appears to encircle the entire Valley, though it is not without a number of canyons, cracks, caves, and other breaches that allow travel between the Valley and the Beyond.
It consists of a range of mountain peaks, sheer cliffs, deep trenches, and gorges near the outskirts which are dangerous to cross and thus discourage most Sharpteeth from coming into the Valley. Many waterfalls pour from the cliffs, supplying the Great Valley with enough water to support hundreds of herbivorous dinosaurs. At least one wall is close enough to the Big Water for storm waves to wash Mo and a Liopleurodon over the Wall.