The Puye Formation is a Pliocene geologic unit on the east side of the Jemez Mountains in northern New Mexico, north and east of Los Alamos, where it underlies much of the Bandelier Tuff. Formed by repeated volcanic and sedimentary pulses tied to vents of the Tschicoma Formation, it consists largely of dacitic volcanic debris, tephra, basalt, and pyroclastic-flow deposits laid down in distinct cycles. Its lowermost Totavi Lentil is less volcanic and rests unconformably on the older Chamita Formation. Especially well exposed in canyon walls and escarpments, the formation is also important as a high-yield aquifer and as a case study in groundwater chromium contamination and natural attenuation.