Why not 'Ray Hartman'? In other words what is the back story, with pertinent details like size of shrub wanted, site conditions...?

Sorry I should have explained better. We love Ray Hartman but unable to find this tree in any local nursery which we prefer. We are looking for 15 gallon/24 box plants to accommodate the city regulations.

So this is a street tree planting? 'Ray' does have certain significant limitations so that looking for an alternative may be the direction you want to continue in.

What Are the Problems With the Ceanothus 'Ray Hartman'? (sfgate.com)

Also buying fast growing, short lived kinds like this in large sizes is sort of a waste of money. If this is in fact a street tree planting does the City have a list of recommended street trees? As well as ones that are not allowed? The more details you can provide the more likely you are to be helped here.

No, its in the backyards. Exact location will be side of a fence separating two properties.

Why would the city have size regulations on something planted in your backyard? That doesn't make a lot of sense.........

This is meant to be as part of privacy regulations with landscaping for new home builds. I don't quite think its odd but then again it varies by region you live in :-)

Can you explain what the regs are? That might help with suggestions for alternative plantings.

It's odd in that the initial size of a plant (15G/24" box) is rarely called out by city regs for anything other than street trees or possibly a front yard specimen tree. So requiring any backyard privacy planting to be of a particular size before planting is indeed odd! Typically the city or other municipality has no say on what or what size plants you can or should include in your backyard (unless it is a tree for tree replacement requirement). If regs exist at all they are usually HOA requirements.

The requirements are simple : 24 box (typically are easy to establish), evergreen.

What I look for:

Any suggestions for nice looking 10-12 ft green foliage trees, flowering in any season, zone 9, will receive plenty sun until 3pm.

There is nothing about a 24 in. box being involved that confers any advantage. Other than the size of the plant top being bigger at the start.

I am a pioneer who has kept a couple Ceanothus alive on the east coast. (I do not recommend other people try this) (and yes, not just 'Gloire de Versailles') The factor GG mentions becomes even more problematic, in my opinion, in a genus like this. The "California lilac" would be especially unhappy in a watered garden if its root system is wallowing in an enormous box of potting soil! Would be interesting to see if Sara M agrees with me, but it seems like starting small(er) is an especially good idea with those.

Just be aware that nursery stock at both the retail and wholesale level is very depleted. Retailers are telling me that they are getting at most 1/3 of what they are ordering from growers. Apparently everyone decided to spruce up their landscapes while sequestered at home. So you may just have to go with what you can find.

I routinely plant large stuff (I'm 64, I don't have decades to wait). But I agree with David that with a water-averse CA native like Ceanothus, I would not plant a large one. The only Ceanothus that is really adapted to garden water is thyrsiflorus 'Skylark' (and the hybrids that are part European species as David noted above) and it is a low, spreading shrub. CA natives don't make root balls in the sense that say, a Japanese maple does. They send roots out far and wide and the longer that they are in a container the more that you have to water the contrived 'ball' and again as noted above, will result in soil that is way too wet for its taste. I have planted 'Skylark' in #5s; when I planted a bank in 'Yankee Point' I used 4"!

I can't think off the top of my head of a tree that will be small enough that is evergreen. The Arbutus options are evergreen, but they get big (although you can prune). There are conifers that might work but my guess is that if you really want a flowering shrub you don't want a conifer. You might also look at Cercidium 'Desert Museum' (used to Parkinsonia) or some of the smaller Acacias, like riciana, pravissima or covenyi. Acacia stenophylla is a great tree but might get too big. There are some nice Banksia but they might be frost tender for you, there are various Podocarpus. What about a citrus or a dwarf olive tree (Olea Little Ollie)? Finally, there are some evergreen maples - A. sempervirens is one.

There, that was my core-dump!

What about Pittosporum; like Arbutus it can be pruned...but I suspect it is a little more amenable to it. There's P. tobira which is surprisingly dry-tolerant for an Asian plant (I saw them seemingly growing without supplemental water in Barcelona) as well as the Antipodal ones. They have flowers that are very fragrant instead of very showy.

SM Growers is a great source for info on plants for CA gardens:

https://www.smgrowers.com/search/basesearch.asp?strSearchText=pittosporum&x=0&y=0

Yeah there are def some good Pitts that would work.

San Marcos is wholesale only and they are out of stock on a huge number of plants (one of my local go-to guys orders from them regularly). But their info is first-rate.