Are you looking for a groundcover or something taller than a groundcover?

it is a good rule of thumb that trees don't really like things growing under them inside the drip line. I would recommend something line bark or mulch with some ornamental boulders for a Mediterranean countryside look. or perhaps some large pots set up on low 2 to 6 inch pedestals with something in them for a more formal look.

Thank you softmentor and buddyben.
buddyben, we're looking for a groundcover, tho it could be a foot or so tall (hence the ceanothus).
softmentor, the area is large enough that it would take many years, if ever, for the drip line to extend far enough to cover the area

hoov, you've come up with terrific ideas.
I had been thinking of germander, santolina,or snow in summer (Cerastium).
But hadn't considered lavender or any of the others. Hmmm....
Food for thought, but not much thought, 'cause we want to plant soon!
sumcool

I'd recommend the Germander or Santolina over the Cerastium, which tends not to be long lived and needs frequent replacing over time. Lower growing Lavenders such as Lavandula stoechas are probably best if you don't want anything or 2.5 feet tall. You might also consider ground covers such as Myoporum parvifolium 'Dwarf Pink Form'. or one of the gray leafed and red flowering Zauschneria cultivars. Tulbahia violacea or T. v. 'Silver Lace' could also look good under olives. Calamintha is another easy to grow and nearly everblooming drought tolerant low groundcover.