Nacimiento Formation Nacimiento Formation The Nacimiento Formation is a sedimentary rock formation found in the San Juan Basin of western New Mexico (United States) and named for the Nacimiento Mountains. It is a heterogeneous nonmarine formation composed of shale, siltstone, and sandstone, deposited in floodplain, fluvial and lacustrine settings, and made up of sediment shed from the San Juan uplift to the north and the Brazos-Sangre de Cristo uplift to the east. It was deposited mostly between ~64.5 and ~61 million years ago, during the early and middle Paleocene. The climate was humid and warm to hot. This unit interbeds with the
Devil's Backbone (rock formation) left an isolated bedrock ridge remaining between two valleys. Rose Island, an amusement park popular during the 1920s that was destroyed by the 1937 Flood, stood on this rugged peninsula, at the base of the ridge on a level area. Charlestown State Park hiking trails do not provide access to the Backbone, but a loop around the old Rose Island site passes below the ridge. There is another location by the same name near Fort Ritner, Indiana, east of Bedford. Devil's Backbone (rock formation) Devil's Backbone is a rock formation and peninsula formed by the flow of Fourteen Mile Creek