Precambrian structures in Canon del Trigo, Manzano Mountains, central New Mexico
— Jeffrey A. Grambling

The Manzano Mountains form a block-faulted uplift along the eastern edge of the Rio Grande rift. They extend northward from Abo Pass to Escabosa, a distance of some 55 km. The range consists of a large mass of Precambrian metamorphic and igneous rocks, overlain by a thin veneer of east-dipping Paleozoic sedimentary rocks. Recent sands and gravels bury the basement rocks to the west. Details of the regional geology are summarized in Reiche (1949).

According to most previous workers, Precambrian geology of the Manzano Mountains is fairly simple (Reiche, 1949; Stark, 1956; Myers and McKay, 1971; Condie and Budding, 1979). These workers have recognized two periods of deformation in the basement rocks. The first deformation affected units in the northern part of the area, where rocks seem to be multiply deformed. This region, north of Comanche Canyon, is separated from rocks to the south by an apparent angular unconformity (Reiche, 1949; but see Blount, road-log segment I-C of this guidebook, for a different explanation). According to published interpretations, rocks south of the unconformity are younger and have been deformed only once.

Estimates of stratigraphic thickness in metamorphic rocks south of the unconformity are in excess of 5 km, whereas the overall thickness of Precambrian units in the Manzanos is estimated as 12.5 km (Condie and Budding, 1979).

The present report summarizes results of detailed mapping of a 3.5 km' area in Callon del Trigo. The mapped area lies entirely within the "Blue Springs schist" of Stark (1956), and it lies approximately 5 km south of the apparent angular unconformity. According to previous structural interpretations, rocks in Callon del Trigo have been deformed only once. However, Precambrian exposures show numerous features which are inconsistent with this simple structural history. These features include multiple schistosities, folded foliations, and refolded folds. Such features are characteristic of multiply-deformed terranes. If basement rocks in the area are multiply folded, then their stratigraphic thickness may be considerably less than published estimates.