The source area of the Yellow River is located in the northeastern Tibetan Plateau, and is a high-elevation region with the annual mean temperature of-3.9℃. The ice-wedge pseudomorphs discovered in this region are recognized as two types.One was found in sandy gravel beds of the second terrace of the Yellow River. This ice-wedge pseudomorph is characterized by higher ratio of breadth/depth, and are 1～1.4 m wide and about 1 m deep. The bottom border of the ice-wedge pseudomorph is round arc in section. Another discovered in the pedestal of the second terrace has lower ratio of width/depth, and is 0.3～1.0 m wide and 1～2 m deep. Its bottom border is sharp. Based on the TL dating, the former was formed at the middle Holocene (5.69±0.43 ka BP and 5.43±0.41 ka BP),that is, the Megathermal, and the latter was formed at the late Last Glacial Maximum (13.49± 1.43 ka BP).Additionally, the thawing-freezing folders discovered in the late Late Pleistocene proluvium are 39.83±3.84 ka BP in age. The study on the ice-wedge pseudomorphs showed that the air temperature was lowered by up to 6～7 ℃ in the source area of the Yellow River when the ice-wedge pseudomorphs and thawing-freezing folds developed.
