Yes, synthetic grass is your answer. It may feel a little wrong, but it's no less artificial from an ecological perspective than your pool, your house, your patio, and most everything else built on your property. All of those things used resources to manufacture and ship from long distances to transform what was originally desert/scrub grassland into what you see today.

I won't even suggest tens of thousands of dollars in cactus.

I won't even suggest native grassland restoration (which would look like "weeds" most of the time and "dead" when they were dormant).

I won't even waste my time suggesting that beauty is in the eye of the beholder.

Roll out the Astro Turf and your problem will be solved.

thank you for your comment. synthetic grass may be the answer but it leaves us with have 3500 sq ft of unusable space because nobody would ever be able to walk on it unless we had stairs built. the turf company said we could basically kill ourselves if we tried to walk up the synthetic grass because we'd end up slipping from it being so slick and hot. so we will continue looking for options. thank you

You mentioned you have plans for a large retaining wall. What about an alternative, installing stairs and terracing instead? You could use the terraced planters for native plants, small shrubs, and veggies!

I think planted terraces would be much more beautiful than a large retaining wall. Not sure on whether or not it would be more affordable, but it seems like something that could be done in stages if necessary.

We purchased a home on an extreme slope two years ago with a history of neglect. The neighbors are forthcoming, so we know the history. The original owner was a contractor/builder. Happily, he installed several terrace systems and paths down the boulder studded hillside. He also installed drip irrigation. Some of his ideas were pretty good, and I'm sure he did it all himself. Not so easy to DIY of you are not a builder, but he used various materials to terrace and make paths for access.

I don't go down the slope without a hiking staff. It provides the hand rail that he didn't.

He used railroad ties vertically for some terracing. He used them horizontally for steps. He secured them with rebar and concrete in places.

Other terraces were made of brick and blocks, all secured with concrete and rebar.

I'll search my computer for photos which may give you ideas. Remember, this is 1.5 acres of neglect and although we have improved it some, we have miles to go! I agree with melle_sacto on steps and terraces with interesting plantings.

Here is one plan using succulents. HE built the steps and patio. WE planted this succulent which needs no water ever. Note the step design:

More ideas for you! Remember we are not yet done fixing all the years of neglect!

This photo shows how he handled individual plant terraces on a slope.

How do you envision "using" the space? If you want to physically use it, without a humungous, expensive, worrisome (would be to me, anyway) retaining wall to make it all flat, terracing and stairs, as melle-sacto points out, is the alternative. Terraces are visually pleasing, and flat areas could be lawns or gardens. We did DIY stone terraces for the down-sloping backyard we had in Massachusetts (there is a lot of easy-to-get, cheap rock in Massachusetts!).

I have similar, steeper slopes surrounding my Livermore, CA backyard. Since I have plenty of flat area for my conventional garden (roses, fruit trees and bushes, etc.), I opted to plant my slopes as-is (no terracing) as a tapestry-like chaparral of drought-tolerant shrubs appropriate to this area, such as Ceanothus ('Ray Hartman' and 'Blue Jeans'), toyon, Yucca, Artemisia californica, Rhus integrifolia, Salvia mellifera, Eriogonum giganteum, Salvia clevelandii, rosemary, etc., to create visual surroundings for the garden. It took several years for the shrubs to fill in, but it is virtually maintenance-free (except for occasional replacement of a dead plant) and that area is not irrigated at all (in fact, an area planted like this should not be irrigated in summer after the first year or two of establishment). I planted it all myself, during the autumns of two or three years, after ripping out the English ivy and ice plant that previously covered the slope.

Here are views of the slope this morning. Even though the plants go dormant during the summer, leaves are retained, though smaller and less lush on some plants than in winter. It really is very green and lush-looking in winter, especially when the Ceanothus are in bloom and the California sages are fat and plumy with moisture.

Terraces can be a viable option. You can build two or three terraces with steps leading up from the pool area. Also, your "hydroseed" grass looks like it could possibly be festuca rubra. If that's the case, it will eventually spread and cover the slope. You will just have to manually keep the weeds from invading so that it doesn't become a huge, weedy mess.

As Josue says, if Festuca rubra (or nearly any native perennial bunchgrass, for that matter, except for Bromus carinatus, which grows pretty rapidly), first-year plants are small clumps and gain size and substance over a few years. Weed control is critical in the meantime so that the grass seedlings don't get overwhelmed.

I so want to go outside and take photos of what the builder did here, but it's friggin raining from that tropical depression. Trailing rosemary is great on slopes. Not only is it beautiful and green with tiny blue flowers, it is drought resistant and edible. I wish the rain would stop so I could go take photos. Laguna is so beautiful! I bet you have gorgeous ocean views! I do think, if for no other reason, winter rains could bring that slope down, so you need to control errosion.

I love the approach that Catspa showed above. It's low-maintenance, ecologically-responsible in multiple ways, much more affordable than options involving geological engineering, and beautiful. I'd rather look at that beautiful chaparral than stone walls or concrete steps. Our urban areas have too much concrete as it is. Catspa nailed it.

so appreciate all these comments & ideas! the photos are fantastic. i think it's fair to say that i've been open to just about anything to make it a usable space. growing up in sweden and having 2 small children...most of our time is spent outside playing. we have used every square inch of our front yard for 'doing life' outside and we just want to be able to do that same in backyard. i have a board of images that ranges from slides & zip line on slope to terraced garden.

Here are some images that I have on my board for ideas...

When we bought our house...we took all the ivy from front slope - 20+ years of ivy was a mess...we planted small creeping rosemary & thyme and lavender and it's really done well. the front slope is significantly smaller than back though...and also has more shade in afternoon from huge trees.

We've even looked in to cost of craning in large oak or olive trees for slope. You name it and we're open to it. I just want it to be usable and a place that doesn't make my eyes hurt (like it currently does). I'm open to all the DIY ideas and willing to do the hard work. This forum is just wonderful to get ideas from so many different people. Thankful for it!

I finally took some photos with a few more ideas for you. My usual disclaimer. Excuse the mess. 1.5 acres takes a while to tame.
Here is our frontage slope planted with rosemary, freeway daisies, sages, agapanthas, etc. There is no hardscape here, but it's very difficult to manage weeds due to the extreme slope.

Suzi...thank you so very much for all these images! So helpful and so great to see what you are doing...it all looks fantastic! Thank you for taking the time to take pictures...so helpful and very thankful this forum is here! Thanks again!

blanchette, I had thought of slides for the grand kids! AND a zip line too! Hope you keep us updated as to what you finally decide to do! Good luck with your project.

I see a few nice photos in there from Suzi, too.

My only recommendation is to start with the vegetation. Hardscape, berms, steps, retaining walls, and other geological engineering features tend to be much more expensive and much less necessary than vegetation. Not to mention more ecologically disruptive. Perhaps a carefully-planned engineering feature could be a critical piece in your landscape. Or perhaps, like Catspa's property, no engineering is needed at all. Nature can often do its own engineering. Think ecology first. Plan your miniature ecosystem first. Traditional thinking tends to want to "tame" or "conquer" nature and it often ends up damaging it or destroying it. You have a wonderful property and a wonderful opportunity. My wish is that it becomes as beautiful and as well-used by wildlife as your family and friends. I don't see California's water problems as a nuisance to be navigated; I see it as a sign of bad sickness in our world as a whole, living way out of harmony with our environments, slowly destroying the very systems that provide for us.

I saw these on a listing for a home in San Rafael. The hill looks comparable in size to your hill.

You gotta love the nice touch of the chicken coop atop the upscale, mid-5-figures, modernist mini homage to the Gardens of Babylon. I keep looking for an escalator. Maybe it's behind the chicken coop.

Forgot to congratulate you, Blanchette, on the conversion of your front yard from English-ivy hell to the nice plantings you now have. I can't imagine why it was so popular in the past -- here it harbored lots of vermin, including rats.

"You gotta love the nice touch of the chicken coop atop the upscale, mid-5-figures, modernist mini homage to the Gardens of Babylon. I keep looking for an escalator. Maybe it's behind the chicken coop."

Haha fair points (btw the stairs are visible in the fourth pic). The yard belongs to a renovated Eichler so the hill treatment fits with the style of the house. That style isn't for everyone, and I'm not suggesting the OP go modern, but it can't hurt to look at a variety of things for inspiration, right?

Catspa, thanks for the great information and the excellent point you make about the overwhelming cost effectiveness. I won't even plant as large as 1-gallon container trees. I plant from bare-root seedlings, no more than 18" tall, or from seed. I've never seen a container plant outperform one from seed or seedling. In fact, I refuse to buy anything from the retail horticulture industry. I've seen it consistently cited that 75% to 90% of the trees people bring home from garden centers end up dead within a few years. That's been my experience as well. By the way, you rock. Restoration ecologist? I didn't know they had jobs that awesome.

If you want "useful"--what does that mean? For use by humans, flat areas are best, which means terracing and stairs. If you want one big flat area then yes a large properly engineered, geologist checked retaining wall is the long term (expensive!) solution. Properly done to code it will add long term value to your property.

"useful" to native wildlife means a different approach with a variety of native plants that will hold in the soil and provide food and shelter to birds and wildlife.

You have to decide if retaining walls/terraces is going to be worth the money. Your kids will likely have no interest in playing outside within a decade--what then?

I will echo what Catspa mentioned regarding the large trees: plant younger trees. Trees, especially trees like oaks, will send out deep roots when young to reach underground water tables, but also to anchor the tree to the ground as it grows. Later in its life, it will send out lateral roots to help stabilize it. These lateral roots are what keep it from blowing over in the wind, or toppling over due to gravity in your case since you'll plant it on a slope.

I have fruit trees planted here and there on our slopes, but again, you will need a way to get up there to pick them, so some kind of terracing or stairs will be important. Fig trees grow large, don't attract bees (no fun in a pool), and the fruit is good to eat fresh and delicious on the BBQ. Their roots are surface, so will help with erosion, but I wouldn't put them close to concrete.

You have so many options! I'd be in your shoes if our hard scape wasn't already here when we bought this place. There is no way we could have navigated the slopes on this property without it.

Is it any harder to walk up a grassy hill or an uphill path than a set of stairs? If the footing is secure, it doesn't make much difference to me. They all traverse the same distance in elevation. In fact, stairs can sometimes be more slippery than sod. And I'd rather slip on a soft grassy hill than slip on a hard set of steps. (By a strange coincidence, I actually have 2 close family members who suffered significant injuries slipping on outdoor steps, but that's another story.) And I'd rather slip on a grassy hill with shrubs to grab onto...than slip on a set of hard steps without a handrail. And with my pets, I'd rather they risk rolling down a hill than tumbling over a precipice and dropping 10 feet or more from atop a retaining wall.

And if stairs are the goal, a retaining wall doesn't necessarily have to be part of the package. You can build a set of stairs right into the side of a hill. You don't even need a path connecting the stairs.

If I were concerned about muddy or slippery ground after rains, I might lay down a gradually winding, meandering sand, gravel, or cobblestone path up the hill, following the natural contours of the land. I'd make its surface rough and grippable. If someone slipped off the path, there would be vegetation nearby to grab onto. But in dry California, a path for rainy days might not even be worth the effort.

One other fun idea might be to string a rope from the bottom of the hill to the top. This could be used for safety in case of slipping. Or on steeper sections that could be climbed on all fours, it could be used like a rope ladder. The rope could even have knots in it every several feet.

And of course there's the world's longest water slide down into that pool. You already have that planned. That would be the envy of the kids in the neighborhood!

And you might also sculpt a couple small terraced areas for sitting in flatter spots on the hill. So perhaps a couple small, inexpensive retaining berms made with logs, no more than a couple feet in height - just enough to make a nice place to sit.

I was just at one of our projects today and what we did was build lower retaining walls and an upper one to level out an area for synthetic lawn. You can't really see it in the photo as we just placed plants today but behind the second retaining wall there is a 30x20' area with synthetic lawn. There is a small deck and planting. The problem with slopes is that unless u really kill the weeds they will just keep coming back you can't just pull the tips off. So maybe you seem to have a sort of flat area in the middle and you can create a terrace effect.

Just tilt the computer screen to view :)

If you are in socal and need a contractor let me know and I can give you a referral. Also the reason your previous project came out so much was probably with walls over 5' high I'm thinking they must have been 6-8' high. those are expensive walls. Short walls are much cheaper.