Geologic map of the Montoso Peak quadrangle, Santa Fe and Sandoval Counties, New Mexico
Dataset Identification:
Resource Abstract:
The Montoso Peak quadrangle is underlain by volcanic rocks and associated sediments of the Cerros del Rio volcanic field in
the southern part of the Española Basin that record volcanic, faulting, alluvial, colluvial, and eolian processes over
the past three million years. The geology was mapped from 1997 to 1999 and modified in 2004 to 2008. The geologic mapping
was carried out in support of the U.S. Geological Survey (USGS) Rio Grande Basin Project, funded by the USGS National Cooperative
Geologic mapping Program. The mapped distribution of units is based primarily on interpretation of 1:16,000-scale, color aerial
photographs taken in 1992, and 1:40,000-scale, black-and-white, aerial photographs taken in 1996. Most of the contacts on
the map were transferred from the aerial photographs using a photogrammetric stereoplotter and subsequently field checked
for accuracy and revised based on field determination of allostratigraphic and lithostratigraphic units. Determination of
lithostratigraphic units in volcanic deposits was aided by geochemical data, <sup>40</sup>Ar/ <sup>39</sup>Ar geochronology,
aeromagnetic and paleomagnetic data. Supplemental revision of mapped contacts was based on interpretation of USGS 1-meter
orthoimagery. This version of the Montoso Peak quadrangle geologic map uses a traditional USGS topographic base overlain on
a shaded relief base generated from 10-m digital elevation model (DEM) data from the USGS National Elevation Dataset (NED).
Faults are identified with varying confidence levels in the map area. Recognizing and mapping faults developed near the surface
in young, brittle volcanic rocks is difficult because (1) they tend to form fractured zones tens of meters wide rather than
discrete fault planes, (2) the youth of the deposits has allowed only modest displacements to accumulate for most faults,
and (3) many may have significant strike-slip components that do not result in large vertical offsets that are readily apparent
in offset of sub-horizontal contacts. Those faults characterized as "certain" either have distinct offset of map
units or had slip planes that were directly observed in the field. Faults classed as "inferred" were traced based
on linear alignments of geologic, topographic and aerial photo features such as vents, lava flow edges, and drainages inferred
to preferentially develop on fractured rock. Lineaments defined from magnetic anomalies form an additional constraint on potential
fault locations.
Citation
Title Geologic map of the Montoso Peak quadrangle, Santa Fe and Sandoval Counties, New Mexico