This is a popular nymph pattern, especially in California and Nevada. It doesn't represent anything in particular, but suggests many things in general.
Hook: Size 8-18 (here, a size 10)
Thread: 6/0, rust
Tail: Mallard flank
Rib: Fine copper wire
Abdomen: Australian possum or other to suit (here, synthetic ginger)
Legs: Same as tail, tied full
Thorax: Same as abdomen
This pattern can also be fished effectively in brown and black.