Stress data show that the contemporary tectonic boundary of the southeastern Colorado Plateau is coincident with the segment of the Jemez lineament between the White Mountains in east-central Arizona and the Jemez Mountains in north-central New Mexico. The lineament is actually a broad (~50 km wide) tectonically active zone that tends N52¿E and approximately coincides with a Precambrian province boundary. It is characterized by extensive late Tertiary-Quaternary volcanic fields, NNE trending (~N25¿E) en echelon faults, and both normal and strike-slip faulting. Pliocene-Quaternary normal oblique-slip displacements have been observed on faults within and south of the lineament but not north of it. Late Laramide NE-SW compression, which caused widespread tectonic shortening throughout the western Cordillera, apparently was transformed into left slip along the Jemez lineament. As the Precambrian basement underwent strike-slip faulting, a belt of NNE trending en echelon faults developed in the overlying Phanerozoic sedimentary strata. By the end of the Larmide orogeny 40 Ma ago the principal structural elements of the lineament, seen today, had been formed. Volcanism in the Datil-Mogollon volcanic field began after the cessation of Laramide tectonism and heated the crust around the southeastern edge of the Colorado Plateau. These elevated temperatures further weakened the part of the physiographic plateau immediately south of the Jemez lineament so that with the onset of SW-NE extension in the southern Basin and Range Province, about 30 Ma ago, this area deformed more in response to the extension than to the stress field of the plateau interior. The emplacement of large NW trending dikes into the area between 27 and 29 Ma ago was directly related to this extensional event. During the late Miocene the direction of spreading changed to a W and WNW orientation allowing the Colorado Plateau to begin a small clockwise rotation. Coeval left slip and extension occurred across the Jemez lineament. Major volcanism on the lineament was initiated by the change in spreading direction. Volcanic activity started at the weakest points first, where the lineament is intersected by the Rio Grande Rift (Jemez Mountains) and Capitan lineament (White Mountains). With increasing extension across the lineament between 7 and 4 Ma ago the NNE trending faults opened, and by the earliest Piliocene (~4.5 Ma ago), volcanism was occurring along the entire southeastern tectonic boundary (Jemez lineament) of the Colorado Plateau.