wow! That's about as tough a spot as I can think of! Wish I could help!

What about something like an ornamental grass? Some of them are taller than they are wide and have nice color, and they would look good most of the year.

I don't know what plants do well in zone 10, but just thinking of "things it would be great to grow if I didn't have to worry about frost"--how about something like bird of paradise? (Not the native one--the tropical one.) Or alstroemeria?

Here is a link that might be useful: California Gardens Plant List

I have a south facing 2' strip against the back of my house. What has done well there are Nandinas, lavender, Perennial salvia, Ceanothus and thyme. I don't water much there (the sprinkler misses it) and they all survive. The lavender and salvias thrive, in fact.

Vegetables do particularly well in California. Perhaps tomatoes. They grow upwards so the small space shouldn't pose much of a problem and they can be tasty. :)

If you want something more colorful you could plant various wildflowers like California Poppies that would look great and stay close to the ground.

Well you limit your options if you'll never do anything for it, of course (you didn't say that, I realize). There are plants that are big bushy beautiful flowering things you might love -- but you would have to TRIM them to keep them from taking over your alley house city allotted space. ;-) Some are evergreen perennials that can be shaped with hedgers.

Another idea since you have full sun is to build yourself a trellis along the wall and grow something super viney that you can 'train' back and forth on the trellis so even long vines would be ok. There's all kinds of stuff that flowers and vines, from faux 'spinach' to beans to flowers. What you'd want to look for is how much they 'bush out', since you could manage the height with careful trellis wrapping but the width could be an issue on some.

When I was in Z10 I had a scented geranium (nutmeg scented) which did great in a spot about that size, and needed nearly no care. It had pretty pinkish-red flowers too!