The decay of cosmic ray-induced 26Al and 10Be in quartz sediments allows the calculation of sediment emplacement ages back to about five million years. Two examples are given: Mammoth Cave (Kentucky) and Atapuerca Cave (Spain). The sediments in the Mammoth Cave System were an integral part of how the cave was formed. The sediments reveal the evolution of the cave system, and how cave development is tightly coupled to river incision and aggradation. In this case, Mammoth Cave was ideal because it was a water-table cave that carried quartz from local bedrock. In contrast, Atapuerca is a sedimentary infill where sediment (and animals) fell into a preexisting cavity. Such cave infills are the norm in archaeology and paleoanthropology because they collect bones and artifacts over long periods of time. In this case, the cosmogenic nuclides dated the sedimentary infill rather than the cave itself.