The 20 Incher Stone is a product of Colorado’s Roaring Fork Valley. Its’ originator I’m not sure of, but I am sure of the effectiveness of his fly.
A simple combination of common materials put together in an ingenious way to imitate the ubiquitous stonefly, (Thank God for the thesaurus!) this fly is a proven killer on Colorado’s freestone streams.
This fly is really a pretty simple tie. The biot tails are perhaps the most challenging part, and the partridge legs can be a bit tricky but even intermediate tying skills will conquer this pattern. I use a small amount of dubbing to form a tapered underbody on larger sizes. This helps the taper to show in the peacock overbody and keeps you from having to use fifty pounds of peacock to form the abdomen. Follow the directions closely for details on preparing and tying in the partridge legs. Keep an eye on the proportions and don’t fall into the trap of making the thorax too short. The thorax and bead should be equal to half of the shank length. Don’t be scared. Like I said, it’s an easy fly, just pay close attention to the details. I guess that’s the key to all flies…