Smaller fish in a stocked lake

Hi everyone,
I'm new to native fish, but I've been in the tropical fish hobby for almost two years. This past weekend I was visiting family in Santa Rosa (California wine country, north of the Bay Area) and took a walk around Lake Ralphine, which is a small, trout- and bass-stocked lake in a local park. We spotted some interesting-looking fish in the shallows, so we snapped some photos and observed for a while, but had no idea what they were. The teenagers working the boat rental booth had no idea, either. When we got back to the house, we described them to my father-in-law (an avid fisherman/hunter) and not even he couldn't tell us what they were. I've been scouring the internet for the past day and a half and still can't find anything, so I figured I'd better just ask.

 Fish 2 - 2012-08-12.jpg   212.09KB   11 downloads

 Fish 6 - 2012-08-12.jpg   236.92KB   7 downloads

Sorry for the terrible photo quality - I wasn't expecting to be photographing anything so all that was available was a phone camera. In lieu of better pictures, I'll describe them and hopefully that will be enough for someone to at least send me in the right direction.

The largest fish were probably about 4 inches long, long and slender rather than high-bodied like the bluegill my father-in-law first mentioned. The base body color was a silvery gray/olive green. They had a dark spot right around the gill cover, and dark vertical bars from there to the tail. They had a single dorsal fin set far back on the spine, symmetrical caudal fin, anal fin, and a pelvic fin (possibly paired, hard to tell), all of which were a bright seafoam green/blue. I'm assuming these were the males.

The females (?) were darker in color overall, with the same banding but no blue on the fins. Their undersides were bright silver.

The fish were swimming in the shallows, over a muddy bottom with about a foot of water. It looked like spawning season; the 'males' were swimming laps around small depressions filled with medium-sized gravel, sparring with their neighbors. One male was chasing off invaders, then allowing one of the darker-colored females into the hollow and swimming tight to her side in circles over the gravel. He chased off a few more males, while another two females slipped into the hollow, and then he was herding all three of them around in circles. He had as many as four or five girls at one point. Shortly afterward all the females left and he went back to solitary guard duty. We soon saw another group displaying the same behavior.

The mystery is killing me! I'd love to know what kind of fish these are, and if anyone can even just give me a starting point for more research, I'd be grateful. Thanks!

Father-in-law is correct. Even from your pictures, you can see the overall body shape and vertical barring on the sides of the fish show that it is a bluegill. Your description in your posts also described typical bluegill.

We call the swimming laps around the nest "spinning up". All members of sunfish family including basses and crappies spin up in some fashion.

Often times when a male (primary) appears to have multiple ladies visit at same, some of those "ladies" are in fact dudes (secondary males, a.k.a. female mimics) cuckholding the male that made and does the courting. The cuckholders are competing with primary male for the role of fertilizing eggs. Those cockholders tend to look a lot like females but if you look closely you can see they are in fact cross-dressors. Another type of even smaller male I call tertiary (a.k.a. sneaker) darts in very briefly while other are spawning and leaves an often visible cloud of milt.