Quaternary and Pliocene faulting in the Taos Plateau region, northern New Mexico
— Stephen F. Personius and Michael N. Machette

The Taos Plateau region of northern New Mexico contains numerous faults that offset sedimentary and volcanic rocks of Pliocene and Quaternary age. This report discusses these known or inferred faults and summarizes the work of Machette and Personius (unpublished mapping 1984). Although previous small-scale maps of the Rio Grande rift (Woodward and others, 1975; Baldridge and others, 1983) showed many of the features described in this report, our work focuses on faults and folds less than 5 m.y. old.

This report discusses some of the prominent faults in the Taos Plateau region and includes data on the amounts of vertical surface offset (fault throw), ages of faulted deposits, recency of fault movement, and morphology of fault scarps. Amounts of offset were determined in two general ways: (1) from direct field measurements of the net vertical offset of surfaces across the fault, and (2) from indirect measurements from 1:24,000-scale topographic maps, aerial photographs, and published data. The direct measurements probably are accurate to within 10% of the actual surface offsets, whereas the indirect measurements usually reflect the range of values that are common along a fault (for example, 5-20 m of surface offset).

Only faults that displace, or are suspected to displace, Pliocene or younger materials are shown in Figure 1. Many more faults may be present in the area. For example, Pliocene or younger faulting probably occurred, but cannot be demonstrated in areas where only Miocene or older rocks arc exposed; most mapped faults in these areas are not shown. In other areas, deposition or erosion may have removed evidence of Pliocene and younger faulting.

Data used to compile Figure 1 are from published and unpublished geologic maps and literature, inspection of aerial photographs, and limited field investigations of Quaternary fault scarps. The geologicmap data are quite variable, ranging from reconnaissance maps at scales of 1:62,500 or smaller to detailed maps at scales of 1:24,000 or larger. Where several sources of data were available, we used the most recent data that focused on late Cenozoic structural and stratigraphic studies of an area.

Our approach of showing only faults for which direct evidence of Pliocene or younger movement exists yields a minimum number of faults. Readers using these data for hazards assessment, regional structural analysis, or other similar studies should be aware that many other Pliocene or younger faults may be, and probably are, present in the Taos Plateau.