You are correct Beaverfan - the OBPC occasionally stocks Commonwealth with ODFW's permission. The goal was to increase warm water angling opportunities. The fish are there - though not in huge numbers, and frankly, I believe they hang out in the places least hospitable to attempting to angle on that body of water (in other words, on the side of the lake covered in the thick, thick brush). The lake is a semi-natural tank, basically. It's gradually sloping on all sides, mud and rock bottom. I've heard there's even a concrete slug on the bottom of the deepest part of the lake, but I don't know if this is true or not. Was told this by a land owner adjacent to the park.
I've had my best success with these fish - largemouth bass, bluegill, and crappie - near the outflow pipe by the dam - but the water level has to be right. The higher the pool the better. Same with carp fishing - I've had a lot better luck when they keep the lake full, than when they lower it a foot.
The few smallmouth bass I've caught there have normally come from the north end of the pond near the inflow "creek". The little lagoon off on the northwest corner has never been productive, despite looking fishier than all get out.
Commonwealth is one of those waters that honestly, I think ODFW would be waaaay better off stopping stocking with hotdog trout, and managing as an honest to god warm water fishery. The only caveat to that - they'd have to screen the outflow better somehow - as right now the warm water fish DO spill into that creek - I've caught every species from the pond in the creek that runs along side it - and that creek IS home to a small population of native cutthroat - and according to the THPRD biologist that helps manage the lake - does occasionally see a steelhead in that little ditch. I would think the cutties, at least, would migrate down stream in the summer, to search for cooler more oxygenated waters.
A good healthy mix of largemouth bass and panfish would be pretty much self sustaining on that pond - provided they set limits on the bass properly. They would have to stock it far, far less than they do now with the hotdog trout.