They're dug out of this yellow soil.

它们是从这片黄土里挖出来的。

This area that I went to is really hilly, arid, a lot of wind, and it's famous for its fine yellow soil called loess.

我去的这个地区确实是丘陵、干旱、风大，并且以黄土的细黄土壤而闻名。