Certain areas have played with the idea of field blends- planting a little bit of cab with your merlot and cab franc, for example. You harvest all of it at once and you get more acid from the less ripe varieties and more sugar from the over ripe varieties and you are good to go. These plantings are extremely knowledge intensive and risky.
The other way to plant a field blend, is to have no clue what you are doing.
Spanish and Italian immigrants back in the day, planted whatever happened to be in their left hand at the time, and they planted it wherever they happened to be standing.
The plantings in some of these vineyards have absolutely no correlation whatsoever with logic. It’s like a really pretty rainbow in the desert.
The craziest part of all of this, is that no one is planning on moving a damn thing. These vines are 60 years old and that would take another 60 years to replace them, which we don’t all have.