It was designated a National Scenic Trail in 1968, although it was not officially completed until 1993. The Pacific Crest Trail, the Appalachian Trail, and the Continental Divide Trail form the Triple Crown of long distance hiking in the United States. The PCT was conceived by Clinton C. Clarke in 1932; however it was not given official status until the National Trails System Act of 1968. (Info on P.C.T. from Wikipedia
Now if you take the Right Hand option, you will be heading to Shadow Lake. But you are actually on the River Trail. The River Trail will also take you to Thousand Island Lake. I believe this option is the best way to get to Thousand Island Lake if that is your destination.
The Shadow Lake Trail is not encountered until a couple of miles up the River Trail and there you will see a trail sign identifying this fork in the path. If you continue on the River Trail, you will follow the river canyon and end up at Thousand Island Lake. If you take the Shadow Lake Fork, you will of course end up passing by Shadow Lake on your way to Ediza Lake.
This trail option will also give you access to the John Muir Trail.
The Northern option of the John Muir Trail will lead you to Gannet Lake, Ruby Lake, Emerald Lake, and finally Thousand Island Lake. This is a longer and more arduous path to Thousand Island Lake (in comparison to the River Trail), but it is a much more beautiful route to the lake districts in my opinion.
If your destination is climbing Mt Ritter, Banner Peak, or one of the Minarets, then take the River Trail Shadow Lake option. Then take the fork latter on that ;leads to Ediza Lake.
This is the best way to access the aforementioned climbing objectives. You could also Climb Mt Ritter
and Banner from Garnet Lake or Thousand Island Lake, or many other surrounding points, but the Ediza Lake route gives you a more direct approach to the peaks.