Grizzly River Run is a rapids ride in Grizzly Peak at Disney's California Adventure. While it's not a "must do," it is also recommended. The minimum height to ride is 42 inches.
Billed as the longest, tallest and fastest "tub-style" river raft ride in the world. Look to get plenty wet, but don't expect the characters and songs that Disney delivered on its "Splash Mountain" log flume rides.