Basin architecture of Pliocene-Lower Pleistocene alluvial-fan and axial-fluvial strata adjacent to the Mud Springs and Caballo Mountains, Palomas half graben, southern Rio Grande ritft
— Mack, Greg H.l Foster, Ron and Neil J. Tabor

In the northern Palomas half graben, adjacent to both the footwall scarp of the Caballo Mountains and the intrabasinal Mud Springs Mountains, the Pliocene-lower Pleistocene Palomas Formation was separated into five mappable facies assemblages, including (1) volcanic-clast conglomerate (VCC), deposited on alluvial fans derived from the hanging wall mountains (Black Range, Salado Hills, Sierra Cuchillo), (2) sedimentary, granitic and metamorphic-clast conglomerate (SGMC), deposited on alluvial fans derived from the footwall scarps of the Caballo and Mud Springs Mountains, (3) sedimentary- clast conglomerate (SCC), deposited on alluvial fans derived from the eastern dip slope of the Mud Springs Mountains, (4) crossbedded sandstone (CS), deposited by the ancestral Rio Grande and (5) fine-grained facies assemblage (FG), representing a combination of deposition on distal alluvial fans derived from the hanging wall mountains, on the floodplain of the ancestral Rio Grande and on distal alluvial fans from the eastern dip slope of the Mud Springs Mountains.

The basin-scale architecture is characterized by (1) narrow (< 1 km) aprons of alluvial-fan deposits adjacent to the Mud Springs (SGMC and SCC) and Caballo (SGMC) Mountains, (2) a narrow (< 2 km) belt of fine-grained sediment (FG) that extended to within a few hundred meters of the eastern dip slope of the Mud Springs Mountains, (3) a narrow (< 5 km), southtrending belt of axial-fluvial deposits (CS) and (4) a broad (15-20 km) belt of alluvial-fan sediment derived from the western hanging wall mountains (VCC). The width of these facies belts and the nature of their interactions are a response to a combination of eastward tilt of the Palomas half graben, the relative size of the catchments and the role of paleoclimate on the erosive power of channels.