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The fluvio-lacustrine sediments in the Nihewan Basin of North China, known as the Nihewan Formation, are well-known for an abundance of Early Pleistocene mammalian fossils (known as the Nihewan Fauna sensu lato) and Paleolithic sites. The age at which the sedimentation started is thus crucial for our understanding of early fauna and hominid occupation and infilling history of the basin, but it is poorly constrained to date. Here we report on a detailed paleomagnetic investigation of the Yangshuizhan section that crops out in the northeastern Nihewan Basin, supplemented by rock magnetic analyses into the carriers of the natural remanent magnetization. Magnetite and hematite are shown to be the main carriers of the characteristic remanent magnetization. Magnetostratigraphic correlation to the geomagnetic polarity timescale indicates that the onset of the Nihewan Formation in this section occurs at ∼3.7 Ma …