Periwinkle is the hardiest evergreen ground cover we have. We have both the evergreen and the varigated. The only care it gets is cutting back periodically with a weed eater. We have it on a steep bank along the roadside and in rocky areas where mowing is difficult. EP

:) diversty is the most important thing to consider when trying to stabilize a slope... you want things with different root depths, even if they're more or less the same height.

I'd jump over to the 'california' forum for zone-specific recommendations, but installing a mix of succulents (like ice plant, prickly pear, and aloes) drought tolerant groundcovers (rosemary, sages, natives) and accent plants (yucca for height and texture, small to mid-size shrubs, and things like Pineapple Sage, which goes from a cutting to a perennial monster in your area in a matter of months) will be your best bet-

and no, you don't have too much time to get the basics in, since they need to be starting root growth when the rains start in what, a month or so?

:) lucky you have the sweaty teens to help :)