31 Stratigraphic Studies in the Colorado Plateau

This session features stratigraphic studies that resolve the geological history of modern and ancient sediment routing systems, and their processes, within the Colorado Plateau using data from field, analytical, experimental and/or numerical modeling investigations.

Tuesday, 19 May 2026
1:30 PM - 4:00 PM
Alvarado C

The lower Permian Yeso Group in the Sandia Mountains, central New Mexico: a critical juncture in the Yeso depositional systems

Paper number: 31-2
Program: Technical Sessions
Time: 1:52 PM – 2:12 PM

Authors

Abstract

In the Sandia Mountains of central New Mexico, the lower Permian section includes the Yeso Group, which is 138 m thick and subdivided into (ascending) De Chelly and Arroyo de Alamillo formations, and the San Ysidro and Los Vallos formations. At Placitas, two stratigraphic sections document over a distance of ~ 1 km the southward gradation of the De Chelly Sandstone into the Arroyo de Alamillo Formation. Similarly, the Placitas area documents the transition from the sandy, siliciclastic San Ysidro Formation (north) to the Los Vallos Formation (south), which is a mixture of siliciclastic, gypsum and carbonate strata. The Placitas area was thus an important area of transition from the De Chelly erg to the arid coastal plain of the Arroyo de Alamillo Formation that extended south to at least Sierra County, and the transition from the siliciclastic shelf deposits of the San Ysidro Formation to mixed nonmarine-marine coastal plain deposits of the Los Vallos Formation that extended nearly to the marine Delaware basin to the southeast.

Correlation of Yeso strata from the Sandia uplift to the Yeso outcrops to the northwest and south indicates major facies changes along that transect. Thus, Yeso correlations show fairly consistent lithofacies from Abo Pass at the southern end of the Manzano Mountains through the Fra Cristobal Mountains. Northward, to the northern Sandias, the Yeso thins, as do its constituent formations. The Arroyo de Alamillo Formation grades into the eolianite-dominated De Chelly Sandstone, and the mixed marine-nonmarine Los Vallos Formation transitions to a more nonmarine, more sandy (with little gypsum or carbonate) San Ysidro Formation. To the northwest, in the Jemez Mountains, the De Chelly and San Ysidro formations are similar to but thicker than at Placitas.

The Placitas area was thus a critical juncture in the Yeso depositional system. This reflected the position of Placitas in the depositional system, which extended from southeastern New Mexico just northwest of the Delaware basin to the southern Colorado Plateau in northwestern New Mexico.  The Placitas area was where the De Chelly erg transitioned to the arid coastal plain deposits of the Arroyo de Alamillo Formation, and the siliciclastic shelf deposits of the San Ysidro Formation began to give way to the more marine influenced coastal plain deposits of the Los Vallos Formation.

 

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410523

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