I have too many citrus for my Citrus Variety Grove in my backyard. I'm thinking of fixing a minor problem of a 5' block wall between my house and the East neighbor by using several "extras" to espalier against the West Side of the North/South block wall in between. They would grow 1-2' above the wall.

It is 10' from each house to the wall in between. Both are one-story low roof houses so the roofs are only 8' above ground level. I have put several citrus in pots in the area and they are thriving but they have only been there during the Summer. Upland was prime citrus country with 300 sunny days per year. Now that Autumn has arrived, or at least the SoCal verson of Autumn, the espalier would be getting about 5 hours of direct sunlight per day. Of course the beginning of that direct sunlight would be shining straight down on the top of an espaliered tree. This seems like it is more direct sun and almost as many hours of exposure to bright blue sky as the north side of the 20' trees in the back. The part of the tree that eventually grows above the wall would be getting direct sun 3-4 hours earlier. Am I missing something?

This is clearly less sun that the open areas but it seems like it should be plenty as long as I pick the cultivar wisely.

Bears Lime?
Eureka?
Meyer?
Satsuma Owari?
Gold Nugget?
Chandler Pomello? Thinking any Pomello/GF needs lots of heat.

Should be no problem. You probably don't have to limit yourself in selecting varieties, either, at least on account of light/heat; the amount of sun doesn't really affect the heat experienced by the plant too terribly much (although it probably does more so in CA than in the humid southeast, I still wouldn't think the difference would be significant; a west wall should be plenty warm, though). That said, it seems like some varieties would work better, architecturally and aesthetically, for an espalier - lemons, limes, mandarins.

I would go with Gold Nugget. It's one of my top three citrus fruits, grows very upright, and ripens late when there will be more sun touching it at your proposed location.

Greg, your two best cultivars for espaliering would be #1 Bearss lime (it grows in a natual espalier shape), then #2 satsuma, whose drooping branches would be quite suitable for espaliering as well.

This seems to be working out. I ended up with a few too many of several varieties: Bearss, Eureka, Satsuma Owari, and Gold Nugget. The Bearss and Gold Nugget Standards have structures that looks like a good start for an espalier. The drooping stucture of the Owarii Standard seems like it would be nice as a single but I want these two to match since they will be side by side along a wall.

I would also recommend looking up what the mature trees look like if you know anyone who has these varieties or on the web.