1- use an excavator or scoop to shovel up the soil & rock mix and run it through a rock separator. Then scoop the de-rocked soil back to the garden area. This is an expensive option and against my desire to work this homestead in a low tech, low impact, low input fashion.
2- do it by hand
Someone suggested running a bulldozer over the ground with a chisel under it. That would at least break up the soil rock layer making it easier to work by hand. But again, it's more than I want to do. Perhaps if I had more than an acre to prepare, but I have a much smaller piece of land to convert to a garden. And more over, the chisel would destroy the lava tube drainage system in this field. That tube system keeps my land from flooding during the "ten-year rain" ........that by the way is well overdue according to the locals here.
Since this land is very rocky, I plan to use it to grow veggies that don't need totally derocked soil. My plan is to remove rocks gradually over a long period of time, eventually having it derocked enough for a rototiller. But that will take months, perhaps a year. In the meantime I will remove rocks as I plant individual plants. For example, if I grow tomatoes I only need a plant every few feet. A hole will be dug just for the plant, not the whole row. Then later on as I have time I can remove rocks from between the plants. This is how I cleared the original 50' x 100' garden.
(Tomato pants lined up so that I know where to dig the holes.)
This time around I don't plan to derocked the walkways. In my original garden I derocked everywhere. Beds. Walkways, Borders. Looking back, there was no need to do all that. Just the growing beds need derocking. That will save 50% of the labor and time.
My tools of destruction will be an o-o bar, a pick, and a mattock. I'll choose whichever is easiest for the particular situation. This will be a work out! Build muscles! Heck, it's cheaper than joining a gym, and more enjoyable. When's the last time your gym workout included tropical sunshine, breezy tradewinds, birdsong and butterflies?
I have to get the ground totally scuffed with the rototiller this week. The grass is starting to grow back and I'm out of vinegar. So far I've gotten over half the new area scuffed and mulched with grass clippings. I plan to work on it again for the next few days to attempt to get it all covered by the end of the week. I'd hate to see the grass grow back after all that work.
This new garden area is going to be used by the community garden group. Today was their first day working the garden area. Wow, it was a joy having people to work alongside. We got a lot done. Lots more rocks dug out. Lots of soil turned over. Plenty of things planted already.
The garden group owns a lot of old plastic piping which makes very visible, easy to handle row delineators. The volunteers marked all the beds that were ready to plant, planted about 2/3 of them, and mulched it all.
So the old pasture is finally a garden! There's still a lot of work to dig out rocks, turn and loosen the soil, but it's on it's way.
So this project is proving to myself......and the garden volunteers.....that a large rock-free garden is do-able around here. It just takes time and work. But I can see that it's work that many people are not willing to do. So far only me and the community garden group seems to be willing to put out the effort. But reaping our rewards will be oh so sweet!
If even one person comes along and says how lucky we are to have soil and no rocks, I'm going to be sorely tempted to bop them one. Luck had nothing to do with it!