Geologic mapping in the foothills of the Jicarilla Mountains near Ancho, Central New Mexico
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Figure 1: Field geologist, Ray Salazar standing approximately at the contact between the Permian and Triassic periods. At this location the contact is poorly exposed, being mostly identified from a transition in the characteristics of float material—the loose regolith and fragments of bedrock that have been transported or weathered from their original position. The Permian-aged Tansill Formation of the Artesia Group is vaguely identifiable in the foreground while red and white horizons of siltstone and sandstone of the Moenkopi Formation are visible in the background. This contact marks an unconformity of over 10 million years during which the Permian–Triassic mass extinction event occurred.
× Figure 1: Field geologist, Ray Salazar standing approximately at the contact between the Permian and Triassic periods. At this location the contact is poorly exposed, being mostly identified from a transition in the characteristics of float material—the loose regolith and fragments of bedrock that have been transported or weathered from their original position. The Permian-aged Tansill Formation of the Artesia Group is vaguely identifiable in the foreground while red and white horizons of siltstone and sandstone of the Moenkopi Formation are visible in the background. This contact marks an unconformity of over 10 million years during which the Permian–Triassic mass extinction event occurred.
2026 Jon Krupnick
Figure 2: A chert pebble conglomerate of the Triassic Santa Rosa Formation in the Chinle Group. At this location there appears to be rip-ups clasts of ~10cm pieces of sandstone and pebbly sandstone. Just a few meters away, this unit is juxtaposed against younger San Pedro Arroyo Formations sediments by a subvertical down-to-the-southwest fault.
× Figure 2: A chert pebble conglomerate of the Triassic Santa Rosa Formation in the Chinle Group. At this location there appears to be rip-ups clasts of ~10cm pieces of sandstone and pebbly sandstone. Just a few meters away, this unit is juxtaposed against younger San Pedro Arroyo Formations sediments by a subvertical down-to-the-southwest fault.
2026 Jon Krupnick
Figure 3: Triassic sediments of the San Pedro Arroyo Formation in the Chinle Group with the plane of a minor fault visible at the gray ledge in the arroyo. This fault exhibited dip-slip motion based on slickenlines observed on the fault plane. The San Pedro Arroyo Formation was observed on both the hanging wall and footwall, so the fault did not juxtapose different geologic units at this location; however, the trend of the fault parallels that of larger faults and nearby mafic dike intrusions.
× Figure 3: Triassic sediments of the San Pedro Arroyo Formation in the Chinle Group with the plane of a minor fault visible at the gray ledge in the arroyo. This fault exhibited dip-slip motion based on slickenlines observed on the fault plane. The San Pedro Arroyo Formation was observed on both the hanging wall and footwall, so the fault did not juxtapose different geologic units at this location; however, the trend of the fault parallels that of larger faults and nearby mafic dike intrusions.
2026 Jon Krupnick
Figure 4: A large chunk of petrified wood found in Triassic-aged strata. I had taken shelter beneath the trunk of a large juniper tree during a 45-minute thunderstorm and this petrified wood was the first thing I observed after the rain let up.
× Figure 4: A large chunk of petrified wood found in Triassic-aged strata. I had taken shelter beneath the trunk of a large juniper tree during a 45-minute thunderstorm and this petrified wood was the first thing I observed after the rain let up.
2026 Jon Krupnick
Figure 5: The contact between red bed mudstones in the Chinle Group and non-correlated surficial sedimentary rocks found on high surfaces in the region. A nearby landslide is partially responsible for the good exposure of this contact. The surficial unit includes weakly consolidated conglomerate with interbedded sandstones, is observed to be several 10s of meters thick, contains only locally derived lithologies, and is capped by a very well-developed petrocalcic soil (caliche). The unit has been correlated to the Ogallala Formation by past geologic mappers working in the region. Paleoflow indicators from imbricated cobbles is revealing a dominant northward flow direction in the few outcrops observed so far. The Jicarilla Mountains is due south of the paleoflow measurements so the deposits seem to be piedmont alluvial fan deposits emanating from that topographic high.
× Figure 5: The contact between red bed mudstones in the Chinle Group and non-correlated surficial sedimentary rocks found on high surfaces in the region. A nearby landslide is partially responsible for the good exposure of this contact. The surficial unit includes weakly consolidated conglomerate with interbedded sandstones, is observed to be several 10s of meters thick, contains only locally derived lithologies, and is capped by a very well-developed petrocalcic soil (caliche). The unit has been correlated to the Ogallala Formation by past geologic mappers working in the region. Paleoflow indicators from imbricated cobbles is revealing a dominant northward flow direction in the few outcrops observed so far. The Jicarilla Mountains is due south of the paleoflow measurements so the deposits seem to be piedmont alluvial fan deposits emanating from that topographic high.
2026 Jon Krupnick
By Jon M. Krupnick, Field Geologist NMBGMR
Jicarilla Mountains near Ancho, Central New Mexico September 11, 2026
Geologic mapping in late August for the White Oaks North and Ancho 7.5x15-Minute quadrangle targeted areas dominated by Permian, Triassic, and Cretaceous stratigraphy that have been deformed by tectonics of the Laramide orogeny and faulting and folding from the intrusion of magma forming laccoliths related to the Rio Grande rift. Structural features deforming the Triassic and Cretaceous strata kept me alert while surficial sediment cover and vegetation obscured the geologic relationships around me. The weather was hot except during minor thunderstorms. There is a lot of work remaining to develop a deeper understanding of the geology in this area.
