The deposits of the Baca and Carthage-La Joya basins record late Laramide (Eocene) sedimentation in west-central New Mexico and eastern Arizona. Sedimentation in these basins was influenced by tectonism (both intrabasinal and in surrounding uplifts) and by the prevailing semiarid climate.

A well-exposed facies tract through the central part of the Baca basin reveals a broad spectrum of depositional paleoenvironments. The braided alluvial-plain system, consisting of the deposits of coalesced humid alluvial fans, is widespread throughout the basin. Sedimentary structures present in these deposits indicate that discharge was increasingly flashy toward the basin center. Meander belt sedimentation was predominantly restricted to an actively subsiding, fault-bounded block in the eastern part of the basin; examples of both fine- and coarse-grained point-bar deposits are present in this area. Lacustrine sedimentation occurred in small flood-plain lakes and in a large, shallow, closed lake near the eastern end of the basin. Cyclic progradation, abandonment, and subsidence of fi e-grained deltas and fan deltas well out into the lake basins prevented development of extensive lacustrine basin-center deposits.

Only rocks of the braided alluvial-plain system are present in the poorly preserved deposits of the Carthage-La Joya basin. Updip retreat of facies tracts in both the Carthage-La Joya and Baca basins reflects waning Laramide deformation in adjacent uplifts during late Eocene time.