One theory is that the northerly wind prevailing in this area has affected Xinjiang. A large amount of silt sand from northern Ningxia, Inner Mongolia and even the deserts of Central Asia has been blown to the Loess Plateau and accumulated. Because the bedrock composition of the Loess Plateau and the bottom of the Loess is different. The landforms in the lower part of the loess are diverse and undulating, but the thickness of the loess deposited in the upper part is generally similar, and has a tendency to gradually become thinner from east to west, which is consistent with the direction in which the loess originated from the west. This shows that the loess was moved from elsewhere.
However, many scientists have discovered that there is a gravel layer at the bottom of the loess layer, and this round gravel layer is typical river sediment. So they believed that the origin of loess was in the upper source of the Yellow River, and it was formed by the river washing down the loess.
There is also a view that loess is neither wind-made nor water-made. It is formed by continuous weathering on the original basis and is native.
There is also a comprehensive view that the Loess Plateau comes from the northwest and Central Asia, blown by strong winds, carried by flowing rivers, and weathered on the local native bedrock. It is formed under the simultaneous action of these three forces.
Just as people endlessly sing about the Loess Plateau, people also debate endlessly about the origin of the Loess Plateau. I hope that one day researchers can give people a satisfactory answer.