The soil is...
much like the rest of Idaho...
The soil is very chalky in feel, and is considered a loam in texture/makeup. It is very high in Calcium, which isn't necessarily a bad thing.
It could use more Nitrates, Ammonium, and Phosphate, which are all general fertilizers required by plants to abundantly flourish.
It is also lower in iron, which could be a problem, depending on the variety of vine. Perhaps I'll add nails beneath the vines when planting. Apparently nails were used in antiquity to cure chlorosis.
Adding nutrients to the soil can be a daunting task: making soil more alkaline can sometime require adding tonnes of crushed limestone. In which case this project would be at an end, due to being located on an Island. However, it looks like for adjusting this soil, it will require adding a couple hundred pounds of nutrients per acre. I'm thinking of starting at less than a half acre size, so that would mean probably only a few bags of soil nutrients.
It will be interesting to see how prepping the soil helps things to grow things.