I probably shouldn't have brought up the topic of swimbaits. When I'm throwing my big swimmies, I'm looking for the biggest fish in the reservoir. Just wanted to say that you shouldn't get discouraged if you don't catch anything initially even after spending a lot of money. I know nothing about the California reservoirs; but from what I read, your bass are highly pressured. There might have been a few bass (or more than a few) where you were fishing. But they might not have been actively feeding bass and they didn't bite your lure.
If I wanted to catch a few bass of any size, I'd probably beat the hell out of the shallow/ shoreline cover with a senko or a finesse jig. There will always be some bass up shallow. That probably won't be the primary pattern, those fish might not even be of "keeper" size. But there will be some bass up shallow willing to bite.
I think you should talk to folks who fish your lake on a regular basis to know where the fish are, and what they are biting.
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1. If they're shallower/deeper, does that mean I need different lures (e.g. use my "deep" diver rather than my "medium" diver) or in the case of some of these, like the spoons and spinners, is it just my retrieve technique that I would adjust (e.g. let it sink further, retrieve slower, etc.)
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I do think you need different lures to probe the different depths, AND change the retrieves from time to time if something isn't producing.
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2. As a beginner, is my time better spent staying in one place and trying the different depths/lures, or testing many locations? Dealing with an outboard motor, two clumsy anchors, and the wind made it a lot of trouble to keep relocating in search of the fish (while the pros strolled by with their trolling motors).
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I believe the whole point with bass fishing is finding out where the "active" fish are, and what they are biting. Find a good looking structure from the lake map, like a point/ ridge/ hump, where you can expect active fish, and test the different depths around that. If you have a fish finder on your boat, it's easier to locate the cover on the structure. Cover on it's own is no good, it's the cover ON the structure where the bass are. Find the pattern, and when you've caught all the biting fish from a location, move on to the next location that fits the pattern.
Always ask yourself why you're fishing wherever you're fishing. The water temperature tells me that it's probably post-spawn/ early summer. Which is both bad and good. The bad part is that the bigger fish probably went down deeper onto the main lake structures. The good part is that they're looking to eat.
Good luck!