Geology of Garfield quadrangle, Sierra and Dona Ana Counties, New Mexico
Authors: Seager William R. , Mack Greg H. 
Published: March 2023

The Garfield quadrangle is located along the Rio Grande in south-central New Mexico, approximately 40 km (25 mi) south of Truth or Consequences. Located in the Rio Grande rift, the quadrangle encompasses part of the Palomas Basin, as well as outlying fault blocks of the Caballo Mountains. Whereas the Rio Grande and its tributaries have sculpted the prevailingly fine-grained, soft sedimentary deposits of the Palomas Basin into badlands, the far more ancient and durable rocks of the Caballo Mountains have yielded more rugged topography, featuring deeply incised canyons, high peaks, impressive cliffs, and a succession of cuestas.

The fault blocks consist mostly of Precambrian granite and syenite, unconformably overlain by Paleozoic and lower Tertiary sedimentary strata. Totaling approximately 885 m (2,900 ft) in thickness, the exposed sedimentary section includes basal Bliss Formation (Cambrian and Ordovician; 33 m, 108 ft thick); El Paso Formation (Ordovician; 152 m, 499 ft thick); Montoya Formation (Ordovician; 116 m, 381 ft thick); Fusselman Dolomite (Silurian; 26 m, 85 ft thick); Percha Formation (Devonian; 19 m, 62 ft thick); Magdalena Group (Pennsylvanian; 277 m, 909 ft thick); Abo Formation (Permian; 141 m, 463 ft thick); Yeso Formation (Permian; 30 m, 100 ft thick); Love Ranch Formation (Eocene; 30 m, 100 ft thick); and Palm Park Formation (Eocene; 60 m, 200 ft thick). Cambrian through Pennsylvanian strata are almost entirely shallow marine in origin, consisting of limestone, sandstone, and shale. Much of the El Paso and virtually all of the Montoya and Fusselman Formations are dolomitized to such an extent that original textures and most fossil remains are obscured. Regional unconformities slightly truncate the top of the El Paso, Montoya, Fusselman, and Percha Formations. Uppermost Magdalena strata mark a transition to nonmarine conditions, and the overlying Abo and Yeso red beds are fluvial and eolian in origin, respectively.

An angular unconformity separates Paleozoic strata from lower to middle Tertiary Love Ranch and Palm Park clastics. The unconformity is a product of deformation and erosion of Paleozoic, Cretaceous, and Precambrian rocks during the Laramide orogeny, and the fanglomerates of the Love Ranch and Palm Park Formations document erosion deep into the basement rocks of Laramide uplifts. Southwest-verging, overturned folds and associated thrust faults, exposed in the Derry Hills, are structural elements of an uplifted Laramide block that extended across most of the southern Caballo Mountains region. By middle Tertiary time this block was deeply buried, not only by Love Ranch and Palm Park fanglomerate, but also by a thick succession of andesitic, rhyolitic, and basalticandesite volcanic rocks; most of these were removed from the Garfield quadrangle by erosion during Neogene evolution of the Rio Grande rift.

Laramide uplifts and basins and the deposits that buried them were segmented in late Tertiary time by normal faults of the Rio Grande rift. In the Garfield quadrangle, major normal faults include the Red Hills and Derry Hills faults, which separate the Red Hills-Nakaye Mountain and Derry Hills fault blocks from the Palomas Basin. Both faults show evidence for late Quaternary movement; movement along the Red Hills fault probably occurred in Holocene time. Slightly deformed playa deposits of the Miocene Rincon Valley Formation are the oldest exposed basin fill in the Palomas Basin in the Garfield quadrangle. Only the upper 15 m (50 ft) of a section that is at least 600 m (1,968 ft) thick is exposed. Much more widespread is the late Pliocene-middle Pleistocene Palomas Formation. At least 90 m (295 ft) thick, the Palomas Formation consists of an axial fluvial fades, the deposits of an ancestral Rio Grande, as well as alluvial-fan and piedmont-slope deposits derived from both the Black Range and Caballo Mountains. Along the eastern margin of the Palomas Basin, fan and river deposits of the Palomas Formation overlapped adjacent uplifts, burying all or parts of the Derry Hills, Red Hills, and Nakaye Mountain fault blocks by middle Pleistocene time. Late Pleistocene and Holocene deposits include arroyo, terrace, fan, and river alluvium related to periods of entrenchment and backfilling by the modern Rio Grande and its tributaries. Erosional episodes resulted in exhumation of the fault blocks and superposition of drainage across them.