Horses are not allowed in the Shoshone Geyser Basin. This alternate route begins with a ford of Shoshone Creek and leads horse parties around the geyser basin on the west side to a junction with the South Shore Shoshone Lake Trail. The 2.3 mile trail stays mostly in the trees and is not a favored route for runners.
Thanks to guidebook author, Tom Carter, for sharing this trail description. To learn more about visiting Yellowstone, check out his book, Day Hiking Yellowstone.