check out the work of Wolfgang Oehme:

https://www.amazon.com/oehme-van-sweden-Books/s?ie=UTF8&page=1&rh=n%3A283155%2Ck%3Aoehme%20van%20sweden

Thank you for the suggestion. I'm in the San Francisco area, ~zone 9.

We didn't create more levels due to budget, and yes, the planters open up to dirt below. They're dwarf so hopefully they won't get too big.

euonymus coloratus

can use a lawn mower to trim, resistant to round-up so you can spray any grow thru weeds without damaging
turns a pretty purple red in fall/winter
also know as wintercreeper

Ice plant seems like an obvious choice.

How much sun does the area get? Looks pretty shady in the photo.......

I doubt you want to plant anything up there that requires a lawnmower to trim :-) And Euonymus fortunei/wintercreeper is NOT resistant to RoundUp or any other herbicide!!

^^^^ ummmm oh yes it is, had it for 27+ years and regularly use round up with NO loss. Recommended by our landscape designer for that reason

Have used the ready mixed RU and custom mix from concentrate
Have used a weed wacker and/or lawnmower on hillside, with no problems

You might want to take that up with the Forest Service and various other agencies that routinely recommend using RoundUp (and other broad spectrum herbicides) to control or eliminate this invasive species!! Unless you have some sort of unique GMO'd strain of wintercreeper that is now RoundUp ready...........but I don't think so.

"WINTER CREEPER CHEMICAL CONTROL - Cut stem treatment with systemic herbicides applied to freshly cut stems is effective in areas where vines are well established on or around non-target species, or where they have grown into tree canopies or onto other vertical surfaces. Stems should be cut as close to the ground as possible and immediately treated with herbicide. A 2 % solution triclopyr (tradename Garlon 3A, Tahoe 3A) and water is effective and can be used at temperatures as low as 400F. Follow-up treatment will likely be necessary. Triclopyr is selective for broadleaf species and may be a better
option if native grasses are present. Care should be taken to avoid contacting non-target species.
For larger populations, foliar applications of herbicide may be more appropriate. A single application of a 1.5 % solution of Roundup Pro (4.75 ounces of a 40% concentrate per gallon of solution) applied as a foliar spray in early September resulted in a kill rate of 25 - 30 % after six months and a 50 % kill rate after 12 months (Solodar 2005). A single application of a 2 % solution of Roundup Pro (6.3 ounces of a 40% concentrate per gallon of solution) resulted in a 40% kill rate after six months and an 80 % kill rate after 12 months. Roundup Pro was most effective when applied to plants that were actively growing and at least one month prior to the first killing frost."

You are referencing a very systemetic way to eliminate it. You have to have fresh cut stems with only a 30% to 50% kill rate.
I use RU all thru the season, except for when it is freshly trimmed. And it is a non-GMO species. Never had a problem

Re-read the last paragraph!! Euonymus fortunei is NOT resistant to RoundUp and implying that is is affording inaccurate information to the OP (any anyone else who reads this)! And there are other desirable plants on the hillside that would definitely be affected were the OP to be spraying RU all over the place.

btw, I was joking about it being GMO'd - NO landscape plants are genetically engineered.

I appreciate the replies and discussion :)

Ice plant is not on the list as we proactively try to remove it every chance we get here in the bay area (it's wildly invasive)

Winter creeper, and anything else that tends to get bushy is also not ideal because our area has problems with rodents who like to nest in such plants. Previously the hill was covered in ivy, and rats.

Looks a lot like my backyard! Ours was planted with some kind of grass and full of weeds when we bought the house. Last summer we killed everything with Roundup and then planted vinca on the whole slope, which is doing very well and starting to fill in nicely. It stays very low to the ground and doesn't require mowing. It will be at least another year before it is thick enough to control weeds, though, so for now I have it mulched and will be putting down Preen soon, etc. I'm also planning to plant some shrubs and hopefully turn the whole slope into a perennial garden of sorts eventually, but for now the vinca is there, looking pretty and controlling erosion (I hope). We also have a big patch of pachysandra on part of our slope, planted by the former owner - it looks nice, but it doesn't grow as quickly as vinca and I wasn't willing to wait that long for it to fill in.

We still need to know how much sun this area receives.

Apologies... It's full sun 5 hours, and then shades over through the remainder of the day.

Dymondia would probably be my first choice. But various sedum/stonecrops could work as well, although they tend to be less efficient at weed suppression. Cotula 'Tiffindell Gold' is another possibility.

I would plant Erigeron near the base but it will needed watered from time to time.