Have you checked to see what your city requires for retaining walls? Height may be an issue. Info may be online.

For something like this, I’d hire a landscape architect to integrate walls, hard scaping and soft scaping in the space. It could be beautiful, but I think needs a comprehensive plan.

You removed the shed. Now you need to clean the slope that was long ignored behind it. Judging by the half buried blue barrel to the right and the old lumber on the left, a good chunk of the buildup behind the former shed is piled up leaf litter from the trees and hedge above. Some dirt slid down the hill too it seems. Clean the slope back down to the original grade.

Remove whatever that black stuff is off the original retaining wall that is still there if at all possible

When the cleanup of the shed removal project is complete, then reassess what you want to do in this corner of the backyard

@christopher good point. I need to figure out how to clean the slope back to original grade. There’s definitely lots of leaf build up which I can scoop up but concerned about the little landslide and how much dirt I can/should remove from it.

I can't imagine that there are more than a couple wheelbarrow loads of actual dirt that have slid down the hill. Most of that looks like organic matter. And you have such a handy loading zone at the bottom of the slope.

@christopher I will give it a try and report back!

You can pin landscape burlap on the slope to prevent erosion and keep down weeds while you decide.

Looks to me like you have more issues that just that corner. I wonder why they stopped the second tier just as it got to the patio? The plastic 'wall' above gives me the impression erosion is a problem for the entire area that surrounds the patio. How deep up that hill is owned by you? You will need to get a landscape architect's help. It's going to take a lot of equipment and I would not assume your area is keen on people changing the natural slopes of woodlands. What you change can impact the water etc. your neighbors might have to deal with. Given the droughts we are living with I would not suggest major plantings in your future. You need ground covers that keep the soil in place and require little water.

Maybe before putting effort/$ into what may eventually not be a good solution, I’d invest in a professional consultation. I’m sure there is lots to consider long term.

IMO the erosion is the first issue after you clean up all the dead stuff that has piled up. That black whatever needs to go but not until you have an actual plan and the materilas for dealing with the erosion. We had this issue and did a second level of yard with a quite high retaining wall with proper drainage built into it we had so much dirt removed from around our house that it piled up to create a hill I planted ivy at the top of the wall so it spills over to cover the cemnet blocks we used and then I planter tyme and vinca for ground cover and lots of perennials . The advice to get a landscape architest is good since this could be made to be qite a nice feature.It actually created a nice outdoor dining space the pic is when we just began doing the deck.

@arcy_gw not too sure but I think that second tier is there because of the pool. See view from the other side, there’s pool equipment up there. Which “plastic wall” are you referring to? There’s a fence at the top of the hill and we own up to the fence. The other side is an empty hill.

Directly up the hill from the chain link fence there appears to be a barrier made of plastic. It takes a jog but appears to extend to the blue barrel on the hill. The pool view shows someone has attempted to keep the hill from falling into the hill with what appears to be railroad tie timbers. The more we see the larger this job appears it's going to be.

I see a house up the hill and behind the trees and hedge from your black coated corner of the retaining wall eyesore. When was this house and neighborhood built? I have a feeling the black coated retaining wall and that slope have existed as is for decades with no problems.

Yes, dry dirt can slide down a slope. Erosion happens, especially around human activity. This is such a typical California scenario as to be mundane. It is not some landslide disaster waiting to happen.

Finish cleaning the slope and reassess. Building a higher retaining wall is probably completely unnecessary. Closer pictures of the actual eyesore would also help along with knowing where the property line is.

it’s probably not much help but i think you require a professional landscaper to deal with that. It might require a number of terraced retaining walls. It looks quite challenging but could be a lovely space

@christopher yes there’s a house behind the hill. This neighborhood was built in the 60s so I assume this slope has survived ok for the past 70 years. We think the precious owner put that black coating over the retaining wall before he built a shed in front of it, to protect the wall and/or shed. I’m reconsidering cleaning up the slope myself because I’m afraid if I scoop some dirt off the bottom by the black eyesore, it’ll cause the top part to fall down more. Thoughts?

If I was cleaning that eyesore corner, I would start at the top of the pile not the bottom and save the dirt for last. The dirt could be useful. Other than the blue barrel and the lumber I can see, how much more trash is buried under there?

You need to get the leaf litter, trash and dirt to all fall down to clean the slope. Start at the top of the pile.

You could add to the already present stonework as a continuation of that. Make it a water feature that cycles in/out of the pool?

Two comments stand out. First, "it doesn't rain much here"; second, "I assume this slope has survived ok for the past 70 years". The rain issue - if you are in a region which is on the dry side now, a heavy rainstorm could cause a flash flooding issue. Second, as with infrastructure which is 70 years old, if maintenance is not performed - or an inspection by a civil engineer at the least - you could have a slope failure. It is hard to know what type of weight is above the wall or if structural changes have taken place at the properties above you which could cascade down to you.

I would have a professional (engineer, not landscaper) assess the site to point out possible issues. If you rebuild any part of it, I would incorporate some type of drain/ditch/trench along the bottom of the wall to help divert possible runoff from running into your house. If you do rebuild, at least a couple of stepped terraces would seem prudent. Then, I would replant with something native that would be beneficial for the slope stability. Not knowing your region, I couldn't begin to make a suggestion. But deep roots, ability to withstand drought, lower in height, and spreading should be qualities to look for in a shrub. You can always intersperse clumps of colorful perennials for pollinators amongst low growing greenery.

@christopher here are additional pics.

@sirella thanks for the insight. Do you have any idea how to go about finding the right person for this? Or specifically how to find a civil engineer. We are in Northern California.

There is nothing unusual about that kind of slope above a retaining wall in WNC where I live either. I take it the property line is the wood fence I see behind the oleander. The landscaper still says, "clean the slope." Get a putty knife/scraper and get that black crap off the wall.

Once the slope is clean you can plant a Ca. appropriate drought tolerant groundcover. Common ordinary aloe vera makes a very good groundcover, but you will have many good xeric plant choices to cover the slope that will slow the normal erosion and help absorb the leaf litter.

I agree with having a professional look at it. if it were my property I would build up the wall in that area by a block or two. That should hold whatever dirt might fall back. I would probably just paint over the black part with special white primer and then some other paint. Scraping off creosote or whatever that tar looking thing is seems like a nightmare. Probably just paint over that whole section of wall.