The Upper Cretaceous Ringbone Formation, Little Hatchet Mountains, southwestern New Mexico
— George T. Basabilvazo

The nonmarine Upper Cretaceous Ringbone Formation in the Little Hatchet Mountains consists of conglomerate, sandstone, siltstone and mudstone. Deposition of Ringbone strata accompanied basin development during an early phase of the Laramide orogeny. Ringbone strata crop out in several areas in the northern part of the Little Hatchet Mountains. Near Playas Peak, the Ringbone Formation rests disconformably on the upper Albian to lower Cenomanian Mojado Formation and is overlain unconformably by the lower Tertiary Skunk Ranch Formation. In its northernmost exposure, the Ringbone Formation is interbedded with the Hidalgo Formation. Ringbone strata attain a maximum thickness of 1608 m and are divided into three informal lithostratigraphic members. Strata in the lower member have a maximum thickness of 120 m and consist predominantly of sedimentary-clast conglomerate derived from Lower Cretaceous and Paleozoic sedimentary rocks that were located to the northwest. Conglomerate successions in the lower member are interpreted as alluvial-fan and braided-stream deposits. The middle member attains a maximum thickness of 1095 m and was deposited by a northeast-draining paleofluvial system that flowed nearly orthogonally to that of the lower member. Delta-plain, marginal lacustrine deltaic and lacustrine deposits also characterize the middle member. Rhyolitic to quartz latitic or rhyodacitic air-fall tuffs permit stratigraphic correlation between geographically separated exposures. Dinosaur remains indistinguishable between Albertosaurus or Daspletosaurus and well preserved hadrosaur skin impressions and skeletal material (vertebrae and ossified tendons) indicate a late Campanian to early Maastrichtian age for this member. The upper member attains a maximum thickness of 393 m and is mainly composed of coarse-grained sedimentary litharenite and conglomerate of braided-fluvial and alluvial origin. Beds of volcanic-clast conglomerate are interbedded with upper member sedimentary strata and increase in abundance in the northern exposure. The stratigmphic relationship between the compositionally distinct Hidalgo and Skunk Ranch formations supports the interpretation that the early Laramide basin, represented by the Ringbone Formation, was partitioned by a subsequent phase of Laramide deformation.