Precambrian geology of the Truchas Peaks region, north-central New Mexico, and some regional implications
— Jeffrey A. Grambling

A complexly folded sequence of Precambrian metamorphic rocks is exposed along the crest of the Truchas Range, a 5 x 10 km area extending from Pecos Baldy to North Truchas Peak in the Sangre de Cristo Mountains, 30 km northeast of Santa Fe (fig. 1). Stratigraphic and sedimentary features of the rocks have been preserved through folding and middle amphibolite-facies metamorphism. Lithologies are broadly correlative to those in the nearby Picuris Range, 30 km northwest of Truchas Peak, as noted by Montgomery (Miller and others, 1963), but the stratigraphy of the Truchas Range is complicated by abrupt lateral facies changes and differential metamorphism.

Stratigraphic, structural and metamorphic evidence supports a unique reconstruction of the Truchas and Picuris terranes prior to offset along the Picuris-Pecos fault, as Montgomery initially suggested (Miller and others, 1963). The pre-faulted terrane consists of a massive accumulation of quartzite at its north end and a thick succession of metavolcanic and meta- sedimentary rocks at its south end (see also Robertson and Moench, this guidebook). Key sedimentary facies changes, reflecting variation from shallow-water platform sedimentation in the north to deeper-water basin deposition in the south, are preserved in the Precambrian stratigraphy of the Truchas Range. When reassembled with metamorphic rocks of the Picuris Range and of the Pecos greenstone belt (south of the Truchas Range; Robertson and Moench, this guidebook), rocks of the Truchas Range indicate that deposition of quartzite along a mid-Proterozoic continental margin was occurring simultaneously with volcanism and sedimentation in a rapidly subsiding basin, possibly rifted, farther south.