I ended up using a Japanese flowering crabapple (Malus floridunda). Much slower growing than I thought. My last resort for lesser height would have been a limbed up shrub like Oleander. Really tough to find an umbrella-shaped tree that maxes out at 20-25 ft.

I have a Chitalpa about 20 years old in my patio. Its only fault is the result of its chief benefit. It blooms all summer, which results in spent blooms dropping all summer. I love it anyway, my wife is not so sure. Al

Arbutus unedo or Arbutus x 'Marina' (not a native per se but a California introduction!)

I love my Arbutus Marina and except for its size would strongly recommend it. Mine is well beyond the 25 foot maximum size suggested. Al

Ceanothis is a real litterbug and fairly short lived. Not a good choice in my eye. If there is already a little shelter there, the cercis is beautiful and has decent fall color and spring bloom, and it's deciduous so you can get some sun in the winter. Mine kind of fry during summer in their exposed situation.
Pea

Thanks everyone for these suggestions. More to research. Have thrown Parkinsonia 'Desert Museum' into the loop as the light shade would be pleasant for sitting under. Liked the idea of Catalina Ironwood, but am told it is messy, which also got me to drop out the Arbutus as well.

I have a Desert Museum Parkinsonia in my yard. It's grown from a 15 gallon pot to about 25' x 25' in 8 years. It never gets watered and I'm in a hot interior valley of Los Angeles. It took about 5 years for it to really start blooming in the spring but last year it was covered with flowers, it also sporadically flowers through out the year, even in the bone dry summer. But it's not a very clean tree. It drops tiny leaves all the time and of course the blizzard of flower petals. It's in an area where that litter doesn't matter but in a patio it might be a problem. It also attracts bees year round, which also might be a problem for a patio tree.

My first thought, based on the total combination of factors described was the California red-bud. If you think the site is going to produce small tree growth California buckeye might also be possible, if the effect of the flowers on bees and the dropping of the buckeyes would not be deterrents.

With that one there would also be winter bark interest.

The original US planting (dating from before or during 1942) of what became the basis for 'Marina' measured 46 1/2' x 8'5" x 45 1/2' during 1994. The material is thought to have been imported from Europe to San Francisco in 1917, so presumably larger examples may be present elsewhere in Europe if not California. I've seen at least one quite apparently misidentified photo in a European book that could easily have been the same cultivar.

I have a city street tree in front of our home. It's the Western Redbud (Cercis occidentalis). One of the things that REALLY irritates me about my tree is the drooping branches. When I checked on Google Images, I noticed most of the trees have that classic umbrella-shape which I would have much preferred.

But mine does not, nor do any of the Cercis trees planted along our two-block stretch. I've attached a Google link - the tree photo'ed shows the 'drooping branch' style (this tree is a whole lot better looking than mine, which gets little water and has very poor shape), as well as smaller photos that show the 'upright/umbrella' shape of other redbuds.

My Cercis has been well maintained - by comparison I have a fine variegated sweetgum 20' away that has grown from a 4' stick to a magnificent 30' specimen in exactly 11 yrs - but the redbud remains a scraggly, uninteresting tree. The blooms are pretty but brief; in Oakland it has little or no fall color. The branches are very brittle - gusty winds are always breaking off 1' branch ends.

I wouldn't plant it again, or at least not this particular variety! If I had to choose a deciduous tree I would have preferred a Chinese pistache, as the fall color is superior and the small leaves break down very quickly.

Here is a link that might be useful: Google Images: Cercis - different varieties?

Oak. Our native coastal live Oak is perfect- a natural. Easily pruned as any hedge plant. Or,train to bring out the Bonsai character.
I saw a thick 20" wide trunk of a Live Oak by a driveway. They had sheared it back to maybe 3' tall and a conical canopy. They take anything.