Sandy loam!
Sandy loam refers to the mineral texture of the soil but not things like organic matter, pH, salt content, moisture availability, growing season, or anything else that's relevant to growing plants. There's also elevation and seasonality of moisture to consider. So if all the other things are lined up, sandy loam can be good soil. Plop that down in Iowa or Monterey or Virginia and you're in business.
The soil at the tranch isn't literally the worst, but the short growing season and lack of irrigation seem like the biggest limiting factors.
If they didn't have stock, they could scrape out a meagre crop. I am certain that they haven't asked the county NRCS guy what kind of stocking rate per acre that soil can sustain, so if the alpacas can't graze, they're going to have to buy food for them.
But the idea that they can build the soil to the point where whatever blah blah blah is stupid given that the growing season is not there and the irrigation is not there.
If you're looking at a piece of land thinking, "These people for the last 300 years had no idea what they were doing," the dumb one is you.