P-h-w, back in the early 1970's my cousin Mark and I took a leave of absence from work. We drove out west for a two month trip. We drove in Yellowstone National Park, Wyoming during the month of June. The day was warm but snow was still on the mountain tops and there was snow patches on the lower level. We stayed at the Fishing Bridge campground and caught are trout limit everyday in Yellowstone Lake. The trout were 12 to 16 inches. We cut onions, butter and cucumbers and put it inside the fish and wrap them each separate in tin foil. Place them on the metal grill above the fire pit. Best tasting fish I ever had.
Have fun and good luck fishing.

No shortage of fishing streams all around there, or if you prefer still water, Glendo Res. is close. Lots of public land in WY. Elk hair caddis is always a go to dry fly. In June the grasshoppers should be in Biblical plague mode so a #10 Dave's Hopper or a foam hopper should give some impressive hits. Any of your western collection emergers and caddis in all stages of development work well. A fav is olive drake. Snakes are just part of life here. We have brown water snakes that can be startling until you get used to them. They are harmless. For the others, WY is a carry state. During snake season the first two in the gun are snake shot. Bring your sunscreen and like WAM advises stay hydrated. You will be about a mile closer to the sun than you are used to.