Expansion in this the main Rio Grande rift started about 36 million years back. Rock debris that eroded through the developing rift-flank highlands, also wind-blown and playa pond deposits, accumulated when you look at the subsiding Mesilla Basin. These fill that is basin, referred to as Santa Fe Group, are 1500 to 2000 foot thick beneath Kilbourne Hole (Hawley, 1984; Hawley and Lozinsky, 1993). The uppermost sand, silt, and clay regarding the Pliocene to very very early Pleistocene Camp Rice development, the unit that is youngest associated with Santa Fe Group in this the main basin, are exposed into the base of Kilbourne Hole. The Camp Rice development had been deposited by a south-flowing braided river that emptied into a playa pond within the vicinity of El Paso.

The La Mesa area, a surface that is flat developed along with the Camp Rice development, represents the utmost basin fill of this Mesilla Basin at the conclusion of Santa Fe Group deposition about 700,000 years ago (Mack et al., 1994). This dating apps free area is approximately 300 ft over the Rio Grande that is modern floodplain. The outer lining created during a time period of landscape security. Basalt moves through the Portillo volcanic field are intercalated with all the top Camp Rice development and lie regarding the Los Angeles Mesa surface.

The Rio Grande began to decrease through the older Santa Fe Group deposits after 700,000 years back in reaction to both climatic modifications and integration regarding the river system with all the gulf. This downcutting had not been a constant procedure; there have been a few episodes of downcutting, back-filling, and renewed incision. This episodic growth of the river system resulted in the synthesis of several terrace levels over the Rio Grande between Las Cruces and El Paso. Continua a leggere