The Cave and Basin National Historic Site is a fan-shaped travertine deposit associated with four thermal spring outlets. Tentative age dating of the travertine mound indicates growth initiated with onset of the late Holocene shift to more humid and cool climate conditions and suggests that the flow of thermal waters was limited during the Hypsithermal, which in turn places constraints on the evolutionary biology of endemic species in the spring system. Two large caves and one collapsed cave structure are developed within the deposit. Cave development is in response to both physical erosion of till underlying the travertine and acid gas attack of calcite that makes up the deposit. This process is buffered by formation of reaction crusts of gypsum on the interior cave walls. Only minor modern travertine growth occurs due to historic flow control measures. Understanding the flow of water through the historic site is critical for long-term preservation.