Las Pilitas nursery has lots of great information. I have used Baccharis pilularis, Arctostaphylos uva-ursi, ceanothus, and Rhus Integrifolia. The last one, "lemonade berry" has the deepest root system and the most stabilizing power.

Here is a link that might be useful: Las Pilitas Slope Advice

thanks - the Las Pilitas site is terrific!

My experience is the same as jxbrown, and I used all the plants he mentioned. At least juniper does not regrow from the roots as Quercus does. Al

Although the Las Pilitas site is anti-drip, you might want to think about a temporary drip set up for the first year. Drip components are cheap and easy to assemble. You can just add a female hose thread fixture and drag a hose over to the drip set up when you need to water. It can be pretty difficult to water on a slope especially if you've let things dry out. The next year you can pull it out or just abandon it.

On my north facing slope I piped sprinklers using impulse type sprinklers for my Baccharis. I planted them 6 feet apart and they soon grew together into a solid cover very effective at weed control. After the first two summers no further watering was needed. The roots are down to about 5 feet. After 10 years or so they become very woody and the trunks are very brittle. To rejuvenate I break off at the soil level a few every year. A new plant grows from the established roots. We have a problem with wild blackberry getting established among the Baccharis and have found using a killing blackberry spray will kill the Baccharis no matter how careful we spray. For this reason we must use mechanical methods. Al

Jxbrown, they may be anti-drip but they are pro-low precipitation sprinklers. I agree with them that low precipitation sprinklers are superior for most homeowners than drip. You can also make a simple system with mp rotators and a hose bib attachment. Mp rotators on the fiberglass shrub riser that Hunter makes works fantastically for temporary irrigation as well. I have let those run on a hillside for hours without run off and they resist wind pretty well.

Jxbrown, they may be anti-drip but they are pro-low precipitation sprinklers. I agree with them that low precipitation sprinklers are superior for most homeowners than drip. You can also make a simple system with mp rotators and a hose bib attachment. Mp rotators on the fiberglass shrub riser that Hunter makes works fantastically for temporary irrigation as well. I have let those run on a hillside for hours without run off and they resist wind pretty well.

Sprinklers, you have to remember that when the shrubs get to a certain height, the ones near the sprinklers block water to the rest of the area. So you must trim back regularly.

I've had no trouble with drippers and natives myself--perhaps because our soil is silty, not clay--and being on a hill, drainage is guaranteed.

Thank you for all of the suggestions (I need to do some sprinkler homework.) Looking at the Baccharis pilularis as my plant solution, as it seems to be the height / shape I need and I would love something that would gradually cover the slope as the old junipers continue to dwindle. However the Las Pilitas site describes Baccharis as a background plant (ie not too attractive) & this slope is front / center of our house facing the street and the rest of the front is planted with OLD non-native stuff like boxwood, cypress, and ivy. I can't do a complete native re-do right now, but gradual shifting would be great. Is this the way to go, or should I look at drought tolerant, erosion control non-natives to fill in that bank with the juniper? (oh our old clay sewer main is laid in the slope, going down to the street - roots are an issue)

Baccharis isn't ugly, it's just boring. It's easy to get started and great for slope stabilization. Decorate it as needed (afforded!) with some flashier plants like Joyce Coulter or Yankee Point ceanothus or one of the lower growing manzanitas. If the space works for taller plants, then the lemonade berry or tall ceanothus are good if you need slope stabilization, but if your slope is pretty gentle, you've got a world of choices. If you want some non-natives, rock-roses and cottoneasters are awfully pretty too. Anything is better than that infernal red apple or, God forbid, ivy. I'd leave the junipers in place and just clean out any dead stuff as it occurs. If you have fire issues with your slope, then a pretty fanatical attention to the removal of dead material is a good idea.

And buy yourself a big packet of California poppy seed and sling 'em around everywhere. If the water/rain is right this winter, you may wind up with a blazing sheet of traffic cone orange just for fun.

Nil13: Thanks for the info about the newer sprinklers. I was not aware of them.

thanks jxbrown - lots of great stuff to look into and hopefully implement!

Have you considered Plumbago auriculata? It is a tough plant and would be happy to cover the junipers. Bonus are the masses of blue or white flowers and Marine Blue butterflies.
Galvezia speciosa or G. speciosa 'Firecracker' may also work. I was shocked at how quickly and easily they grew in my garden. It may depend upon how hot your slope gets. While galvezias prefer some protection, your junipers may shade the roots and allow them to thrive. Their red flowers attract hummingbirds.