Seed mix for building soil, on thin soil and rock

On our family land we have a serious amount of bedrock. I'm located in central NY so we get a lot of rain but it doesn't stick around. We do have fields and scrublands with soil but mostly less than 6 inches and never deeper than a foot, a good portion of exposed bedrock too. What sort of plants should I consider and in what ratio, I would like to have as much diversity as possible while being nutrient balanced if that makes sense. Any input is greatly appreciated.

Is it sloped?

Its more like  "stepped", so theres slopes in certain areas. Imagine the ends of different rock layers sticking out, I'll provide pictures tomorrow if it helps.

Will you have animals? Using it as forage and them as fertilizer spreaders greatly speeds up the process, IF you manage the animals--mob grazing, avoiding compaction and erosion, etc. I would plant more annual forage every time you graze a paddock.  Exact mix depends on the time of year and your climate. I have no clue what grows well in your area.  You can check with local extension service or even big ag seed suppliers that support organic or cover cropping. For a paddock sized for one day for a handful of livestock, you can easily broadcast the seed by hand out with a little hand-crank spreader. Do it BEFORE you let the animals into the paddock so they can trample the seed into the ground for better germination.

If not, you are going to have to do the work of mowing and trampling down the crops.  Not sure how easy or hard that will be, but I am guessing harder based on "stepped just."  You won't have the extra biology from the cow poop, so adding some compost or compost tea would definitely help.

The seed mixes should be as diverse as possible. Sun hemp is a huge soil builder if it grows there, but so are plain old oats. There are a couple cover crop seed companies that sell in small quantities, but this is a hard one to buy economically because you need WAY more than a couple seed packets for a gardener but you aren't a farmer buying by the pallet or truckload.  I have used 50 lb bags of oats sold as horse feed, sunflowers as bird seed, etc.  
Get creative.

Nicholas Tedford wrote:Its more like  "stepped", so theres slopes in certain areas. Imagine the ends of different rock layers sticking out, I'll provide pictures tomorrow if it helps.

Ok. The reason i asked is that catching erosion would be quicker than using plant material. I had a cedar post laying on the ground and on the uphill side it collected an inch or more of soil. I am considering a long run of logs after seeing what this one post did. The log will add to it as it decomposes.

I use round bales to feed my cows. It's amazing how little topsoil is actually added when a 6" thick circle of hay is left behind. There's speculation that the green plant material in a compost pile shrinks 90% when it decomposes. So actually building soil to any depth seems like a long process. Setting traps to catch the sediment and keeping roots in the ground to stop it might be a good double whammy effect.