50 year old slope sounds $Approximately$ stable, especially with the 20' buffer below.
i think you could do this with plantings. i approx agree with norminn and hallerb (person who replied in parallel reply), most
of the others...

find a plant oriented reveg/erosion company that doesn't restrict themselves to only natives (an inexact term of course)

or you could hire me for a cheap list of tough plants. they won't all survive the gophers, but some of the species will annoy
your gophers. you can then fill the dieoffs with the survivor species. this requires a lot less work than "construction".

i live near mt. diablo. 20 years and not counting. :-)

I will try 'pinging' recent group of your posting, because your newsgroup address looks very fake:
wheel in
.net:

Yes that's the entire slope. Our property (1/2 acre) was graded 50
years ago so that part of the slope became flat and downhill form that
became steeper than the natural hillside...so the slope does continue
at the bottom of my problem area, but that continuing slope is 'safe'.
This is Califorina, the soil is clayish I believe. House is above the
slope, but the flattened area is a good 20' wide, here is no
immdeidate danger of it being involved in the 'overslope'
erosion...but I don't want to lose the hillside at all if possible.

There are no gullies etc.

needed only when drainage needs fixing.

The hill was grassy (with a few bushes) till

usually baccharis on sunny "never planted" clay.
other shrubs mix in as you go more toward the coast (bollinger cyn, castro valley, oakland hills) and northfacing.

last year when a gopher colony took root, and they've been
accelerating the 'slide' of the hill. I wiped them out last year but
they've returned. So looking for a way to mitigate the effects of the
loose dirt they push out. They put out so much dirt last summer than
this year the grass didn't return with the winter rains as it usually
does...so all summer the slope was mostly just exposed dirt. The new
gophers are less numerous but it seems to be shaping up into a
continuous battle, they're not easy to get.

I'm not sure if there are any ag stations around here, the is the east
bay part of the SF Bay Area. I may have to resort to some professional
type, though some I've talked to seem fairly clueless.

dealing with marketing , construction, marketing , and marketing issues leaves no time for plant (knowledge) :-)

It's not quite
the situation for a real retaining wall but that's the "regular" thing
to do...so I hear that.

Re plantings, I know that would help. But in my case, with gophers
pushing out finely granulated soil, I think I need something like this
terracing idea to keep the soil from sliding down the hill...it's just
at the slope where gravity takes over.

In article .net,
says...
wheel wrote:
I have to deal with a hillside that has a 2:3 slope (if I'm saying
that right, slope goes down a two feet for every three out). The
main goal here is to forestall erosion, secondary to help plantings
take root. Hillside is about 70' wide, and it drops 10'. It has a
mild contour to

Is that the entire slope, or just the portion on your property? ie,
are you on the top or bottom of a mountain?

it, so straight terracing wouldn't be ideal. Anyone have ideas re a
good material for the 'retaining walls'. I'm not really aiming at a
full strength retaining wall system which would probably cost a
fortune to install. More hoping that some easy going terracing will
do enough. Like, steel pegs knocked in two feet deep, with 1 foot
up, and some barrier material as the wall...what that would be I
don't know, but have wondered if there is some recycled plastic
3/4" x 1' king sized benderboard material out there. Or are there
'systems' for this type of situation? I'm not eager to use the
cement blocks that are common, too much weight to haul, it'd be a
lot of block. There is no snow or freezing where I live.

That is a pretty large piece of ground to rearrange. Is there
erosion now? Gullies? What is at bottom of slope? Where is your
house in relation to the slope? Soil type? Trees? Native plants?
If you are just dealing with a graded part of a building lot with a
few bare spots, I'd fill in the washed out soil first. Plant
something with good root system. Laying down a little flagstone with
landscape cloth behind it would help keep soil in place til plants
fill in. I would consider taking some photos to county ag extension
service - they should be able to offer advice (free) and give tips on
what to plant that doesn't require high maintenance.