Reconstructing the westernmost extent of a late Paleozoic Ouachita-Marathon-Sonoran (OMS) collisional orogen between Laurentia and Gondwana requires insight into deformation age and provenance relations of linked hinterland structures and foreland depocenters distributed across the SW US and NW Mexico. Final emplacement of the Ouachita-Marathon collisional orogen in western Texas took place in early Permian (Wolfcampian, ~293 Ma) time, but regional relations farther west indicate that foreland subsidence, arc magmatism, and hinterland-foreland deformation continued into middle Permian (Roadian, ~272 Ma) time. For example, west-derived middle Permian (Roadian) turbidite strata in the western Delaware basin of western Texas contain distinctive Cambrian detrital zircon grains likely derived from basement of the contemporary Florida uplift in southwestern New Mexico, concomitant with foreland subsidence recorded by youngest strata of the Pedregosa basin in southeastern Arizona and adjacent Sonora and Chihuahua.

Western orogen reconstructions also require restoration of displaced crustal blocks of the orogen now elsewhere in Mexico to their proper late Paleozoic positions within Pangea. Apparent absence of Gondwanan continental basement in the orogenic hinterland of northwestern Mexico historically represented a vexing deficiency of the western part of the OMS orogen; however, several workers have addressed this critical shortcoming by invoking subsequent translation of Mexican pieces of the late Paleozoic orogen during breakup of Pangea. For example, the Acatlán-Oaxaca block of southwestern Mexico represents a key displaced crustal fragment of the westernmost end of the OMS orogen. The block comprises an eastern domain of high-grade Grenville (1.3–1.0 Ga) basement and a western assemblage of Pennsylvanian-middle Permian forearc rocks, the two domains separated by a 275-270 Ma (Wordian) ductile dextral shear zone. Stratigraphic relations in the Acatlán forearc include mixed siliciclastic and carbonate mass-transport complexes containing olistoliths of Wordian limestone correlative with similar debrites of the Las Delicias Formation in the Coahuila block directly south of the Big Bend region of Texas. Pre-Pennsylvanian exposures of the Acatlán-Oaxaca block thus represent an unparalleled transect of the western orogen's stratigraphy, igneous history, and hinterland, although timing and means by which the block arrived in southern Mexico remain debated. Nevertheless, emerging geologic relations and new models indicate that the middle Permian configuration of the Gondwana-Laurentia collisional orogen extended to what is now the Pacific margin of northern Mexico.