Well, let’s see. First off, with that much ice on the creek, it must be mid winter. So check the regs to see if the water is open.
With air and water temps like that, the fish are not going to be very active. You can probably forget the riffles, and the pockets also will not likely hold fish in those conditions. Concentrate on the pools, and plan on getting deep and moving the fly slowly.
The odds of a fish coming up on an icy Intermountain West or other Mountainous Western stream for a dry are in the 1000:1 range. Forget the dry flies. The odds of a fish moving even for a well presented wet are better than for the dry, but still pretty tough.
Since it is a fast moving freestone, there probably are few if any midges in the system ( they are a slow / soft water creature ). It never hurts to trail a small midge dropper in a situation like this, but I wouldn’t count on it being very productive. Probably better to trail a soft hackle p.t. or hair’s ear or copper john.
Stoneflies should be plentiful, with a good variety from small black stones, to skwalas in some systems, to golden stones to salmonflies. A fairly large, dark, weighted stonefly fished under an indicator would be my first choice, with a lighter color stonefly my second choice, trailing a p.t., grhe, or c.j. Cast it far enough above the drop into a pool that it has a chance to get down.
If not stoneflies, just some heavily weighted ( tungsten comes to mind ) nymphs in the size 12 to size 18 range would be my next choice, fished as described above.
These are tough conditions to fish. One day might be great, same rig on another day may not produce anything. But from the place you are describing, it would be a great place to spend some time with or without a fly rod in hand, and whether you get skunked or feel some tugs on your line.
John
That is T-shirt weather after the last month or so here.