The Western River Railroad is Tokyo's version of the Disneyland Railroad. Instead of circling the entire park, the Western River makes a B-shaped circuit around the Adventureland and Westernland sections of the park.
You start in Adventureland, where you circle around the Jungle Cruise, though you won't see much of it through the thick foliage. From there, you continue along the edge of the park to Westernland, where you make a circuit around the Rivers of America. You'll pass Indian villages and enjoy a fine view of the river before proceeding into Big Thunder Mountain.
Once past the dinosaur bones, you'll be transported back to the Primeval World, to see the dinosaurs while they were alive. After witnessing an epic T-Rex-vs-Stegasaurus battle, it's back to the train depot in Adventureland.