ok to clarify I live in clay wet area so my advice is definately as far from expert as you can get on this forum....
I would say ..from
common sense..that I would put some shallow swales cross the hill either horizontally or at some slight angle, and maybe even a herringbone style with each one down the hill sloping at the opposite angle??
This would allow the moisture that does run off to go to the next and next..but my guess is that probably horizontally completely would be the best bet..I would try that first.
I would fill each
swale with whatever organic material you can come up with..see if there is any industry in the area that has organic waste that you could get..or just use the manure and
hay and pine boughs..(don't think I'd cut the trees though)..or rake up the leavings from the pines..needles, bark, etc..that is on the ground, but fresh boughs could be cut off bottom branches as well.
those would somewhat acidify the soil..if there is a coffeehouse nearby as for their grounds..(that is what I mean by an industry with organic waste)..
If you have some other wood product parts that you could put into the swales all the better, and if you have access to some non alkaline topsoil, you might see about tossing some of that in the mix on top as well..but that is likely too expensive to do much for you..
My guess is the swales and organic material will give you some planting areas..then I would plant some
fruit trees or nut trees to start out. They generally will take much more alkaline soils than some other garden crops will, most prunus, pears, etc will do fine on alkaline soils..and wont' mind the gravel..you might be able to come up with some clay kitty litter to add some to the soil, but avoid the scented or clumping kind, just get the plain clay kind..and apply it quite widely broadcast..
After your fruit trees have grown for about 4 years (if they are smallish) or 2 or 3 years if they are bought at the 5' or so heigh originally..you will begin to get some leaf litter from them that will help to build the soil..I also would plant, same time as the fruit trees, some legumes for nitrogen and some comfrey or rhubarb or swiss chard with the fruit trees to bring up nutrients and provide you some
mulch materials..and allow some insectory plants to grow to bring in your pollinators..and beneficial bugs..
After say 5 or 6 years you should begin to have some decent fertile soil around the area to be able to plant pretty much anything you want, except maybe blueberries and potatoes?