The Lincoln Folds, Lincoln, New Mexico Edward J
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New Mexico Geological Society Downloaded from: http://nmgs.nmt.edu/publications/guidebooks/15 The Lincoln folds, Lincoln, New Mexico Edward J. Foley, 1964, pp. 134-139 in: Ruidoso Country (New Mexico), Ash, S. R.; Davis, L. R.; [eds.], New Mexico Geological Society 15th Annual Fall Field Conference Guidebook, 195 p. This is one of many related papers that were included in the 1964 NMGS Fall Field Conference Guidebook. Annual NMGS Fall Field Conference Guidebooks Every fall since 1950, the New Mexico Geological Society (NMGS) has held an annual Fall Field Conference that explores some region of New Mexico (or surrounding states). Always well attended, these conferences provide a guidebook to participants. Besides detailed road logs, the guidebooks contain many well written, edited, and peer-reviewed geoscience papers. These books have set the national standard for geologic guidebooks and are an essential geologic reference for anyone working in or around New Mexico. 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One printed copy of any materials from the NMGS website or our print and electronic publications may be made for individual use without our permission. Teachers and students may make unlimited copies for educational use. Any other use of these materials requires explicit permission. This page is intentionally left blank to maintain order of facing pages. NEW MEXICO GEOLOGICAL SOCIETY a FIFTEENTH FIELD CONFERENCE THE LINCOLN FOLDS, LINCOLN, NEW MEXICO Edward J. Foley Consultant, Alpine, Texas INTRODUCTION other steep slopes in the area. These notches and slip- ping surface scarps may be seen to advantage on air In this paper only those folds on the north side of photos (figs. 2, 3, 4) . Scarps in concentric semicircles, the Rio Bonito, in the immediate vicinity of Lincoln, depressions on the dip slopes of these, and hummocky New Mexico are discussed. They occur in an area of topography in general may also be observed. All of about 15 square miles and are believed by the writer to these are quite characteristic of landslides. The slipping have originated as massive landslides or slump. His surface above the old highway slide opposite Salazar interpretation is based on several days of field work at Canyon is obvious on the air photos. These slip sur- Lincoln in 1951, and on six years of general familiarity faces, of course, may be considered as faults, though with the geology of this entire region. During the field they are superficial, not deep seated. work he was accompanied by Mr. D. G. Garrott of the Humble Oil and Refining Company. The town of Lincoln is situated in southeastern Lin- coln County, New Mexico. It lies near the bottom of a deep canyon at an elevation of about 5,700 feet. The top of the surrounding plateau just above Lincoln lies at about 6,400 feet. The Capitan Mountains, six miles to the north, reach 10,230 feet, and Sierra Blanca, 6 miles to the southwest, attains an altitude of 12,003 feet. Average rainfall around Lincoln is about 15 inches a year. However, the present climate and vegetative cover have no direct relationship to the problem of the origin of the Lincoln folds. Upstream from their confluence at Hondo, the Rio Bonito and the Rio Ruidoso flow through the Permian Yeso Formation, which is composed of soft sandstone, siltstone, shale, gypsum and thin limestone beds. Over- lying the Yeso is the weak Glorieta Sandstone. The rims of the canyons consist of the resistant San Andres Limestone, also Permian in age. Thus, a situation exists • in which soft, fissile strata are overlain by thick compe- Figure 1. One of the small folds in deformed area on tent beds. Oversteepened slopes in the soft materials bank of Rio Bonito near Lincoln. are likely to be developed under such circumstances. The processes of erosion that result in such slopes also encourage landslides as well as mass slump as succeed- PREVIOUS EXPLANATIONS ing events. The folds at Lincoln have been variously explained DESCRIPTION OF THE DEFORMED AREA as crumpling between the massive San Andres Lime- stone and the igneous rock (Semmes, 1920), as drag In writing of the folds at Lincoln, Talmage stated folds (Talmage, 1935), as landslides (Panhandle Geo- (1935, p. 153-154), "In the vicinity of the best expo- logical Society, 1939), as disharmonic folding, and as sures, the folds seem patternless; some are inclined to- having resulted from forceful intrusion of sills related ward the east, others toward the west, and some pitch to the nearby Capitan Mountains pluton. The most re- steeply to the south, others to the north. In one case, cent work published on the area is "The Origin of the a strongly asymmetric fold is overturned to the east, Lincoln Fold System, Southeastern New Mexico" (Crad- and its western limb is broken by three small faults dock, 1960). This last paper also describes other rough- overthrust to the west." One of the folds is shown in ly similar folds in the same general region which have figure 1. It is doubtful that adjoining folds are connect- been well known for many years, including the Y-0, Six ed as shown by Craddock (1960, fig. 2, and p. 39). The Mile Hill, Border Hills, Picacho and Tinnie folds. All rocks in this deformed area show many slightly open of them are complex and difficult to explain but, unlike fractures, a condition typical of slides. Such openings the Lincoln folds, where only the Yeso Formation is de- are not likely to exist in folds of deep-seated origin. formed, they all have one thing in common — the San Small notches mark the traces of the apparent upper Andres Limestone is also involved in the folding. Crad- structural boundaries with undisturbed strata assigned docks explanation of these other folds and their origin to the uppermost part of the Yeso, Glorieta, and San appears to be valid. But, in the writers opinion, the Andres Formations. The mountain face just north of same explanation cannot be applied to the folds at Lin- Lincoln Canyon is probably the slightly eroded main coln, nor should the words "Lincoln Folds" have been scarp of an old slide. This also applies to some of the included in the title of Craddocks paper. 134 Figure 4. Stereo triplet showing northwest end of deformed area. There is about a one mile gap between this view and Figure 2. Note huge slide mass opposite mouth of Salazar Canyon. This was caused by Rio Bo- nito and later reactivated by highway excavation. There are other perched slide masses along canyon walls, such as on east side of Salazar Canyon just below the fork. NEW MEXICO GEOLOGICAL SOCIETY • FIFTEENTH FIELD CONFERENCE One very important reference is a Highway Depart- dercut its bordering cliffs, doubtless flowed slightly ment sign opposite the mouth of Salazar Canyon, a few northward of its present course. miles northwest of Lincoln. It warns against the slide A large open rift near the head of Baca Canyon is area on the highway there! shown near the northeast corner of figure 2. It repre- sents the initial movement on an old slide which never ORIGIN OF THE FOLDS did progress more than about 30 feet down the canyon wall. This rift is about 500 feet long. It also may be The deformation at Lincoln probably is the result seen in figure 2. Nearby is another incipient slide with of massive slumping. In late Pleistocene and early Re- an open rift about 100 feet long, 10 feet wide and 5 feet cent time there was a great deal more precipitation in deep. the area around Lincoln than there is at present. At There are three sink holes on the plateau near the least one glacier existed in the nearby Sierra Blanca, head of Baca Canyon, and these suggest that solution and doubtless the rest of that range and the Capitan of underlying material may have contributed slightly to Mountains had a more or less permanent snow cap. the origin of the slides. Incidentally, the steeper dips on Melted water from this ice and snow formed torrential the limestone plateau near the very head of Baca Can- streams, whose violence and carrying power is shown by yon are so close to the Capitan Mountain pluton that river gravel that contains boulders as large as two feet they are undoubtedly associated with the uplift caused in diameter. Although the main glacial cirque on Sierra by its intrusion. Blanca drained into the north fork of the Rio Ruidoso, The deformation in the beds bordering Rio Bonito most of the northeastern part of the range drained into at Lincoln does not extend to the southern side of the Rio Bonito. Salazar Canyon, above Lincoln, carried canyon. If these steeply dipping beds are resistant nearly all the runoff from the southern side of the west- enough to crop out on the north side of the canyon, they ern part of the Capitan Mountains.