The Bofecillos Mountains area of Trans-Pecos Texas contains a Tertiary volcanic vent and a varied sequence of lava flows, tuff, ash-flow tuff, and associated conglomerate, sandstone, and mudrock; after most of the volcanic activity had ceased, the area was block faulled and later dissected into a rugged high-standing terrain with striking exposures. The present study is a continuation of mapping in Trans-Pecos Texas supported by the Texas Geologic Atlas project of the Bureau of Economic Geology; emphasis in this report is placed primarily on thc volcanic stratigraphy and the structural and geomorphic evolution of these rocks to their present stage.