No. 092026-10-19
The Loess Plateau's soil was carried by wind from the deserts
The layer of loess on the plateau, tens to two hundred meters thick, did not weather out of local rock — the wind brought it. For over two million years, winter winds have lifted fine dust from the northwestern deserts and gobi and dropped it over today's Shaanxi-Gansu-Ningxia region, piling up a plateau.
So the loess grains grade from coarse to fine as you dig down, like page after page of a wind's almanac; a layer of dust, then a layer of ancient soil, records every swing between dry-cold and warm-wet epochs. The loess is loose and stands in vertical cuts — which is why cave dwellings, houses dug straight into the earth, exist here.