The formation correlates with the Cordito Member of the Los Pinos Formation. It can be divided into three intervals based on the source of its sediments. The first interval derives its sediments from basement rock of the Tusas Mountains and from the San Juan volcanic field. The second interval is rich in eroded Amalia Tuff and is interpreted as erosion of the edge of the Amalia outflow sheet. The third interval is entirely composed of debris of the Latir volcanic field. These intervals reflect development of hte early Rio Grande rift, with the final interval showing that tilting to the east in the San Luis basin was initially slow enough that debris from the Latir field filled the basin and overflowed to the southwest.