All that slow water is not really all that great, that area is only about 2 1/2 miles from where I live, and I have fished the creek ever since I was about 12. The Penitentary is my favorite spot for big suckers and squaws (2-4lbers) using a big white breadball, preferably no weight. The trout mainly hang out behind big rocks in the rougher water, whirlpools, and currents pouring into calm water.
You will mainly find smaller Squawfish and Redside Shiners in the slow water around that stretch, that spot by Muchos Gracias does look very promising, but I don't think it's ok (only spot I've never attempted). I have pulled out plenty of decent trout up to 16 inches throughout the whole penitentary stretch, even some Cutthroats, just drifting worms and split shot. I also mastered the basics of fly fishing in this stretch, I have gotten a few up to 15-16 inches on the fly, lots of shiners.
I did land a 29 3/4 inch trout up by Walter Wirth from a swimming hole on the Creek years back, but I think it was a gross planter trout from the pond. Some Rainbows, Cutthroats, and Squaws right under the Bridge by Wirth.
Riverfront Park is another place to consider, I do a lot of Carp fishing there, and the Smallmouth are starting to show their faces lately where Pringle Creek dumps in.