Rainbow Falls

Rainbow Falls is said to be located somewhere in the vicinity of Hanging Gardens State Park within the Green River Gorge, and was referred to by name (though likely an unofficial name) in several of the Harvey Manning-era hiking guidebooks for western Washington that were published in the 70s and 80s. As of yet, the exact whereabouts of this waterfall remain a mystery.
A couple of possibilities seem the most likely scenario - Rainbow Falls may have been an unofficial name which was applied to Maid of the Mist Falls near the Franklin Bridge erroneously, or it could also have been given to the ephemeral waterfall which plunges into the gorge just downstream from the Franklin Bridge and Maid of the Mist Falls, or it may occur where a resurgent stream percolates to the surface along the cliffs of the gorge in an area where roads and trails provide no access, and if this is the case it seems unlikely that it is a large stream (or may have gone dry since).