Ancient cities are excellent spatiotemporal indicators for the study of historical human activities and environmental change. The ancient city of Sanchahe is located at the southern margin of the Mu Us Desert, China. It is an ideal location for studying the complex relationships between historical desertification and human activities. Field observations of the ancient city walls, a well, and a spring, as well as 14C dating, grain size, spatial analysis of archaeological sites, and analyses of historical seismicity, indicated that neotectonics may have contributed to crustal uplift and accelerated fluvial incision of the Wuding River. This rapid incision caused a decline in groundwater levels, which is an important reason for the irreversible environmental degradation around Sanchahe city over the past 800 yr. This study provides new evidence for such environmental degradation and may contribute to a better understanding of historical desertification in the Mu Us Desert.

Geological records have shown that the deserts east of the Helan Mountains in northern China were covered by grass during the Holocene Optimum, whereas during marine oxygen isotope stages 2 and 4 distribution of the deserts was almost the same as at present. The wide advance–retreat cycles of the deserts may have exerted an important control on grain-size changes in the loess of the Loess Plateau by altering the distance between the source and the accumulation zone of the loess. This challenges the widely accepted model that winter monsoon winds were the sole factor responsible for spatial and temporal changes in loess texture. To observe spatial changes in sedimentological characteristics of loess during the last glacial–interglacial cycle, the texture of loess was measured along a north–south transect of the Loess Plateau. This transect consists of nine loess sections, starting at Yulin in the transitional region between the Loess Plateau and the Mu Us Desert and ending at Weinan in the southernmost part of the Loess Plateau. Southward changes in sand (>63 μm) content along the transect suggest that variations in desert extent have indeed played a significant role in loess grain-size distributions, particularly in the northern part of the Loess Plateau. It is proposed that sand content (>63 μm%) of loess in the loess–desert transitional zone may be used as a proxy indicator for proximity to the desert margin.

Eolian sand dunes and sand sheets are extensive in the semiarid regions of northern-central China. Previous studies indicated that these eolian sands mainly formed during historical times. However, the sand sources and their reworking processes have not been well studied, and even the reasons for their occurrence are still controversial. Field investigation and sedimentary evidence indicate that both the inner Mu Us Desert and its southern marginal region, both sources of modern eolian sand, are largely associated with reworking of sands of the last glaciation. Based on geological, documentary, and archaeological data, three phases of land cultivation during the past 2300 years, together with historical droughts, high wind energy, and the easily reworked sand sources, largely account for the occurrence of active sand dunes and sand sheets in the Mu Us Desert.