The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large brown trout that only touch streamers for the rest of the year.
This specimen is 14 mm. Technically this is the subspecies T. h. hecuba. The Cascades, Sierras and further West is where the other subspecies, T. h. pacifica is found. The Great Basin seems to have formed a barrier preventing any overlap in their distribution.