We did the loop on Aug 10, 2019. We started from Agnew Meadows. Hiked to Thousand Island Lake via High Trail. On next day, we hiked back via Shadow Lake trail. If I do this again, I probably choose River Trail to hike back becasue I feel Shadow Lake Trail is a mile longer but did not offer any better views. The really nice views are between Thousand Island Lake and Garnet Lake.
My GPX track, Mammoth Lakes - Thousand Island Lake Loop.gpx, can be downloaded from GPS Tracks Collection.
Sunrise at Thousand Island Lake