Mr. Smarty Plants is having trouble visualizing such a long narrow planter. Is it more like a flower bed with a hard border? He doesn’t think that trees would do well in this situation, but shrubs are definitely a possibility.
Lets start by looking at our Native Plant Database which has 7272 species of plants to look at. Go to the Recommended Species Lists box, and click on View Recommended Species page. Clicking on Southern California on the map will bring up a list of 208 commercially available native plant species suitable for planned landscapes in Southern California. This list is too large, so lets go to the Narrow Your Search box on the right side of the page and make the following selections; select California under State, shrub under General Appearance, perennial under Lifespan. Check sun under Light Requirement and dry under Soil Moisture. Click the Narrow you Search button and you will get a list of 37 species for your consideration. If you click on the scientific name of each species, you will get the NPIN page for the plant that contains a description of the plant, its growth characteristics and requirements, and in most cases images. As you check out each plant, you can note its size and whether it is evergreen and produces fruit, and thus determine its level of messiness.
I did the search and found these five plants that look interesting to me.
For help closer to home, you might want to contact the folks at the Los Angeles County office of University of California Extension.