This is where the Western part of the Tonto Trail starts. If you come from the Royal Arch Route, you have to climb out of Garnet Canyon onto the Tonto Bench. Take water from the Colorado River, since Garnet Canyon is
extremely mineralized and is considered undrinkable. Here you can find some useful distances: nps.gov/grca/planyourvisit/upload/Tonto_Distances.pdf
Keep in mind, that it's another 11 miles from the western Tonto Trailhead to Bass Upper Creek Crossing.