San Jon Canyon is located in the Pecos Valley section of the Great Plains of New Mexico, the area is relatively flat till the edge of the plains. 


The Ogallala Formation caps the plains to the East and forms the Mescalero escapement which is the Eastern boundary of the Pecos Valley. 

The Ogallala Formation was deposited during the late Tertiary (Miocene to Pliocene, it's a thick eolian    

The Pecos River has eroded the overlying Ogallala Formation from the base of the Sangre De Cristo Mountains by river erosion. Layers of the Ogallala Formation do exist under the exposed rock layers in the San Jon Canyon but are not visible, as the area is higher than where the formation was deposited.


The Western boundary of the Pecos Valley is defined by the discontinues mountain ranges, the underlying rock of the plains is mostly Paleozoic limestone which is why there are so many caves and sinkholes in the area. 


Looking down from the Great Plains


Most of the layers located in the canyon are too young to be named and thus remain nameless. The age these layers are dated to are around 10,000 - 15,000 years old. 

The Unnamed layers are Modern Playa (Temporary Lakes). They are formed by depressions in the High Plains region, which periodically fill with water after spring storms and summer monsoons. 

Saltwater Playas also form in the Great Plains but are filled by water supplied by underground Aquifers. The salt moves up through the soil and dissolves into the water, then when the water evaporates the salt is left behind. 


The depressions are formed in several different ways. The most widely accepted theories are that they are formed by wind, areas with poorly developed Fluvial drainage systems, underlined by unsaturated clastic / calcrete systems or ground subsidence (sink Holes). 



The Geologic Story of the Great Plains

Geological Servey Bulletin 1493 (USGS)


The Ogallala and Gatuna Formations in the southeastern New Mexico region: A progress report

New Mexico Geological Society 

John W. Hawley, 1993, pp. 261-269

Carlsbad Region (New Mexico and West Texas), Love, D. W.; Hawley, J. W.; Kues, B. S.; Austin, G. S.; Lucas, S. G.; [eds.], New Mexico Geological Society 44th Annual Fall Field Conference Guidebook, 357 p.

Playa-Lake Basins on the southern high plains of Texas and New Mexico: part 1. Hydrologic, Geomorphic, and Geologic evidence for their development  

W. R. OSTERKAMP, WARREN W. WOOD; Playa-lake basins on the Southern High Plains of Texas and New Mexico: Part I. Hydrologic, geomorphic, and geologic evidence for their development. GSA Bulletin ; 99 (2): 215–223. doi:<215:PBOTSH>2.0.CO;2 

National Geographic: Erosion 

Resource Libary - Encyclopedic Entry


Bison antiquus (Ancient bison) 

Prehistoric Fauna

The Teacher-Friendly Guide to the Earth Science of the Northeastern US

The Great Plains

National Science Foundation

Paleontological Research Institution

EPA: Playa Lakes 

United States Environmental Protection Agency