Salmo G wasn't Lake Crescent at one time, in recent geological history, connected to Lake Sutherland which is connected to the Elwha?
Makes sense to me that a type of large lake dwelling cutthroat may have evolved within the Elwha watershed as evidenced by the presence of crescenti in Lake Crescent. If thats the case then a portion of this forms gene pool may have been isolated in the current Elwha watershed first by the geological seperation of the two lakes. The second isolation but not totally complete of this portion would have occurred with construction of the dams. Now in Lake Crescent the Beardslee and Crescenti evolved together with no known hybridization due differing life histories. If the crescenti portion that may have been isolated in the remaining Elwha system were then forced to interact with large anadramous type rainbows which were also somewhat trapped by the dams well then you have a combination which could cause hybridization and possibly produce 12 pound hybrids. I'd recommend a read of Trotters bok on Cutthroat. On the Sol Duc and most other rivers hybridization probably does not occur to any great degree because the causes of large scale hybridization just haven't occurred.

Gooose