The Mühlbach series has been given as evidence for a Late Pliocene/Early Pleistocene Aare–Rhine fluvial system in northern Switzerland and southwest Germany. We show that these deposits represent a variety of different units. At the type location, luminescence dating indicates an age of 55 ka, and we interpret the deposits as slope reworking. Beside methodological implications, our studies recommend caution regarding the interpretation of stratigraphic units for which limited data are available.