If you are looking at a maximum height of only 6-8', then you are looking at shrubs, not trees. 'Full privacy' typically means evergreen and I am unfamiliar with what broadleaved evergreen shrubs are best suited to your area. However, a mixed shrub 'hedgerow' type planting that includes both evergreen and deciduous plants will provide excellent (if not "full privacy") screening plus offer extended seasonal interest as well as wildlife habitat. And eliminates any 'gaps' that could occur from the failure of a single plant in a monoculture hedge. Since you have a mixture of light conditions, that broadens the selections available. I would consider rhododendrons, pieris and kalmia as evergreen suggestions (possibly boxwood or Japanese hollies also) if sufficiently hardy, mixed with fothergilla, hydrangea, spirea, clethra, shrub dogwoods and dwarf lilac for the deciduous components but the choice is up to you and there are almost endless possibilities. Also, dwarf conifers could be included as well.

You don't seem to be getting much joy here, so you might want to search the California Forum which seems fairly active. I went to the CA forum and did a search in the top box "Search in GardenWeb" with the word "shrubs" and chose the option that popped up for limiting the search to the California Forum. Here's one thread that popped up that might be useful to you. I didn't check beyond that, though there were many other threads that looked like they might help, but often a search will give you a bunch of info that pertains to your situation. Since you know your situation best, it helps if you give as much information as possible, such as you want to have the center of the yard available for family activities (as you stated two posts up) or you have a dog that likes to patrol the border or . . . A few general comments: If you use a mix of plants with clusters and repetition of plants along the wall, it will give you some variety and if one plant dies, you don't have to search for an exact replacement since there is already variety in the mix. I wouldn't do one huge block of one type and another huge block of another type - that always looks awkward to me and has the same issue of replacement as well as if a disease takes them all out, you are left with nothing, whereas a mixed shrub border rarely all dies at once. Consider small trees with branches that will reach above the wall as part of the mix to vary the height so that it doesn't end up feeling like a fortress of green. You might also want to consider vines on a trellis along with shrubs and small trees. Trust me, plants really won't add noise screening, though your wall will; I just want you to have realistic expectations. (I live in the boonies where in places there is something like 1/4 mile of woods between me and traffic, and noise decreases due to distance but not any different due to taller plants vs. open field.) If you can add to the top of the wall, that will improve sound screening a bit, or you can add ambient noise to your yard that may distract, such as a small water feature with dropping water (perhaps not appropriate in your arid climate) or plants that rustle when the wind blows. The plants will provide visual privacy, however, and that seems to be your main focus, and will add appeal to the wall from both sides once they reach over the top. How far to put them away from the wall depends on several factors, including how big the wall's underground foundations are; how wide the shrub is supposed to get (take half of the shrub's reported width and since this is given usually at 5-10 years, add a couple of feet since it will usually get larger) and this will be the distance from the wall to aim for; and how much time you want to put into pruning in order to maintain that width. It's a long stretch of wall, and it sounds like you have a family, so you probably want to choose something that doesn't need a lot of trimming. Another maintenance thing to consider is water. Since many areas now have watering restrictions in CA, I'd plant things that will be OK if you can't water them at all for a season. They will need water the first season while they establish, but after that should be able to survive without. Plan on using mulch (I am not sure what type is appropriate for your area, since although organic mulches such as chopped leaves or shredded bark is most appropriate here, I often see inorganics such as gravel used in low water areas.) Ask on the CA forum once you have your plants chosen which mulch would be best in your area. Mulch will help reduce weeds and increase moisture retention. Good luck. I'd love to see what you end up with. PS - I'd also add your location and zone to your profile so it posts along with your name. That way everyone knows where you are before opening your thread, and you may get more helpful responses. Here's how: Go to Your Houzz in upper right of every page, click Edit Profile, and on the left side click advanced settings. Well down the advanced settings page is a blank labeled Climate Zone for Garden Forums along with a link to find your zone. If you add info on your state or the nearest large city you will get even better information since zone only relates to average coldest winter temperatures. Then return to the top of the page and click Done Editing.

Lilacs are not going to like a poorly draining area very well. In fact, not all that many shrubby plants will. The dogwood is a good choice but the orange stemmed varieties tend not to get very large, so not so great for screening purposes. I'd look at other cultivars of Cornus sericea or alba for some rapid growth to size and lots of tolerance for wet soils. Clethra alnifolia is another good shrub for damp soils. And there are various shrub willows that will work also - Salix integra, Salix purpurea 'Nana' or Salix caprea 'Pendula'. And there are lots of perennials that will work but don't exactly provide much in the way of screening :-)) Giant reed grass - Arundo donax - is considered an invasive species in many areas of the country so double check with your state before planting these.

Evergreen plants will also drop spent parts on the neighbor's lawn. And probably also shade it out more effectively than deciduous trees. So now there are two other aspects of the proposed scheme where a tall planting over along the fence may not be the optimum way to achieve the desired level of privacy. In other words if you don't want to affect the neighbor's lawn at all, including merely dropping leaves etc. on it you are simply not going to be able to have a tall hedge or screen along that fence line. It's too bad the wire fence isn't the maximum height allowed by local codes (6 ft.?). Then you could achieve a lot of screening merely by covering it with vines, such as the clematis. This approach would occupy minimal horizontal space and vigorous kinds like that develop rapidly. Even this arrangement would still produce a shadow, generate debris - and in addition would have to be pruned to keep it close to the fence - on both sides of the fence. A big part of the problem is that the neighbor's have done nothing to give themselves privacy from you, on their side of the fence. I have the same situation here. In addition I have had them reach over my similar height wire fence - I am not the one that had it installed, would have gone to the full 6 ft. height allowed if I had - and cut off part of a screening planting I had in place, throw the prunings down on my side of the fence because "it drops leaves on our bark". So I took the planting out. Now they complain about my sensor activated flood lights, which "shine in our bedroom window". Point being is if there is any possibility of similar reactions from your neighbors you again may want to instead focus on doing what you can over near where you are when you think you are too open to view, instead of over by the fence.