some last year on a slope and it cover in one season. Fast grower, occasional yellow flowers. Drought resistant after establishment.

Phlox is a nice evergreen ground cover and it does spread quickly, however you have a huge amount of space to cover and one plant type might get boring.
I'd go with a simple mix of sturdy perennials (daylilies, sedums, carpet roses and St. Johns wort too)planted in large drifts.
In any case you are still going to need to mulch these beds.

Is this a picture where the Massus lives? Really nice pictures. Cannot remark on the landscaping.

Shot