I have not fished the Gros Ventre but I am seen it and am somewhat familiar with it. I would think a 9ft 5wt would work just fine there If you can take two rods to that area I would recommend a 4wt and a 6wt. The same for the Hoback. Flat creek in Jackson Hole, in the Elk Refuge, is a challenging place to fish and in August the terrestrials (Hoppers) would work great.
A little farther south is the Green River right above Pinedale Wy. I have fished it and would highly recommend traveling the hour or so south to fish that river. There is good access via BLM land. Turn left off off Route 191 at the Warren Bridge and from the bridge upstream is all BLM land with good access to the river.
Last edited by VaHunter; 01/18/21.
