I first tied the WD40 in the early 1990's. Although I learned about it on the San Juan River, I was told it was a Colorado pattern.
I believe the pattern which I copied is the original version. The WD in WD40 stands for Wood Duck and the fly was tied with only this material plus the thread and hook. There are no other materials. All the other WD40s that add dubbing and other materials are modified versions of this simple but effective original.
I believe the pattern below is the original.
AmericanFlyFishing.com - Patterns: Fly Tying, WD 40
It is tied similar to the original Pheasant Tail Nymph as tied by Frank Sawyer, except thread rather than copper wire is used. Here is the only known video of Frank Sawyer tying the original pheasant tail nymph using only copper wire, a hook, and pheasant tail fibers.