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.
But the body was not segmented.
It's probably a Tipulidae (Crane Fly) larva. The lower Owens is the wrong habitat for rhyacophilids (Green Sedges). The specimen sounds too big for the hydropsychids (Little Sister Sedges) that low in the system.