Approach & presentation is the name of the game here. These fish don't often get overly selective on fly patterns, but they spook easily and won't tolerate a bad drift!
Fish upstream, dress in earth-tone clothing, and keep a low profile. Stay back and make longer casts in slow pools. Get closer and keep as much line off the water when fishing pocket water.
Hang on a little bit longer. Fishing in the high country should start to pick up in a couple of weeks!