A cannon sits to the right, just past the Frontierland sign on the entrance walkway from the central hub. In the tongue behind the cannon is a classic Mickey, formed by a hole and two bolts.
A Hidden Mickey is under the soap dispenser next to the handwashing station, which is located next to the exit toward the Big Thunder Mountain Railroad Ride.
Study the metal grillwork between the smokestacks and high above the front of the boat for a sideways classic Mickey.
While on a Riverboat on the Rivers of America, look out for three boulders in the water that form a classic Mickey. The boulders are on the right side of the ship near the shore of Tom Sawyer Island and across the river from an Indian scene.
On Tom Sawyer Island is this classic Mickey depression in the rock. As you exit the raft onto the island, turn left and look above the first cavern entrance you encounter.
To the right of the entrance for the Mark Twain Riverboat is a painting "advertising" river excursions on the Mark Twain. The painting is on a wall of the "Shipping Office." Take a close look at the passengers on the lowest deck (inside the yellow box in the picture).