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Home , Madera Group, South Baldy (New Mexico)

The Quebradas (Spanish for “breaks,” Note: All mileages given below are from the a rugged or cliffy area) is a region of north end of the Back Country Byway, at the splendid scenery and easily accessible “Quebradas Back Country Byway” sign (Mile geologic exposures. Rocks from some of 0.0) on A-152. All coordinates for latitude and the most eventful times in our geologic longitude are WGS 84 datum. All UTM read- past are exposed along the Quebradas ings are NAD 83. Back Country Byway, in particular safety sedimentary rocks of , , Late Cenozoic, and The 24-mile-long road is dirt; a age. and Upper high-clearance or 4-wheel-drive vehicle strata are also present. This short guide is recommended. The roads in this will provide you with some explanation area receive infrequent maintenance. of the geologic features visible at ten Loose gravel, washboarding, gully- numbered stops. ing, tight turns with limited visibility, potholes, and rough arroyo crossings all getting there pose potential hazards. Call the BLM The Quebradas Back Country Byway Socorro Field Office (575-835-0412) is east of the Rio Grande between to check on road conditions. This is a Socorro and San Antonio, New two-way road; drive slowly and carefully Mexico. The 24-mile-long dirt road and watch for oncoming traffic. Flash can be accessed from the north via I-25 floods can occur during times of rain. or from the south via Highway 380. It Watch for snakes, scorpions, or other is most often accessed from the north hazardous animals. This is a desert area: end, via Exit 152 (the Escondida exit) Take plenty of water with you, wear a off I-25, just a couple of miles north long-sleeve shirt, long pants, and stout of Socorro. After exiting the freeway, shoes. Use sunscreen, and take maps, turn right (east) and follow the Back a GPS unit, or other navigation aids to Country Byway signs east, then north keep from getting lost (cell phone service toward Escondida Lake. In just over a is limited or non-existent). Tell some- mile, turn right again at the Escondida one where you are going and when you Lake sign and head east, past Escondida will be back. There are no restrooms or Lake, crossing the Rio Grande. At the drinking water available along the route. village of Pueblito (a T-intersection), Be aware that the byway crosses private turn right (south) and proceed about a land, and there are private inholdings mile to the junction of the Bosquecito within the BLM lands in the Quebra- Road with the Back Country Byway das. Do not cross fence lines on private (A-152). This is mile 0.0. Follow the land without permission and stay clear road to the left at this junction. of grazing livestock. All archaeological From the south: The turnoff from sites are protected and should be left 380 is 11 miles east of the village of San undisturbed. Antonio (380 is accessible from Exit 139 off I-25). Turn north onto A-129 and drive 3 miles to the junction with A-152. Turn left here; Stop 10 is just west of this junction.

Route map for the Quebradas Back Country Byway. Distance is 24 miles from end to end. Motorized travel is limited to designated routes within Wilderness Study Areas.

1 At the foot of these volcanic AGE THICKNESS STOP 1 exposures is the town of Socorro. Just GEOLOGIC AGE UNIT STRATIGRAPHIC UNIT IN REGION myBP (feet) The Geologic west of the southern part of town you S 0 can see a white scar on the hillside Quaternary unconsolidated sediment 0–100 Framework T 1.8 marking the Dicaperl Minerals Corp. Santa Fe Tertiary 0–2000 Mile: 2.7 mine and plant, which, since the O Baca Formation and volcanics mid-1940s, has produced perlite, a 65 Coordinates: N 34°06.592’ Mesaverde Group 0–800 glassy, water-rich silicate rock which P W 106°49.495’ expands greatly when heated. The Upper 0–1000 Cretaceous Dakota Sandstone 0–200 UTM: Zone 13 resulting lightweight product is used in 100 the manufacture of insulating materi- Lower 331860E 3775840N 1 145 absent 0 als, ceiling tiles, soil amendments, and Looking west from the top of the small hill many other products. The operation 200 just north of the parking area you can see reflects the long mining history of the Chinle Group Triassic 0–1000 the (the massive Socorro–Magdalena region. From 252 ridge forming the far skyline) and a series the 1870s to the early 1900s this area absent 0 of lower mountains just east and northeast was a major producer of zinc, lead, of the Magdalena Mountains (from south copper, and small amounts of silver, Guadalupian Artesia Group 0–325 ~270 to north: the Chupadera Mountains, gold, and manganese. Scattered mining San Andres Formation 0–975 Socorro Peak/M Mountain, Strawberry continued into the 1940s. Although 0–400 Peak, Polvadera Peak in the Lemitar those mines are now closed, this Permian Yeso Formation or Group 1000–4300 Mountains, and the Sierra Ladrones). legacy is reflected in the presence of There are Paleozoic sedimentary rocks in the Institute of Mining 230–1700 most of those ranges, but volcanic rocks and Technology (New Mexico Tech) in 299 make up most of the outcrops. Socorro. 0–390 These ranges mark the northeastern Socorro is one of the few places in edge of the Mogollon–Datil volcanic the interior of the United States that Late field, which extends westward into sits atop an active magma body. The Atrasado 750–1000 Arizona. The Mogollon–Datil volcanic pancake-shaped magma extends 35 Formation field contains 20 identified volcanic miles north-south from Bernardo to Group Madera caldera complexes (“supervolcanoes”) San Antonio at a depth of about 10 Middle Gray Mesa Fm. 300–500 with an eruption history spanning 12 miles. The progressive inflation of the million years, from 36 to 24 million magma body has made Socorro the Pennsylvanian 0–600 years before the present time (m.y. most seismically active area in the state. Early b.p.). During that interval this was Socorro also lies along the Rio one of the most volcanically active Grande, a river system that is seen 323 regions in the world. Many individual from this stop as a narrow, green strip 354 absent 0 eruptions produced more than 24 cubic extending north-south through this 417 miles of rock, ash, and pumice into desert landscape. The river stretches 443 the atmosphere. The largest eruptions the length of New Mexico from yielded 240 cubic miles of such material Colorado to El Paso (Texas) and the 490 (compare that with the roughly 0.24 Gulf of Mexico. It flows within one 543 cubic miles erupted during the Mount of the major features of New Mexico granitic basement St. Helens event of 1980 and the 6 cubic geology: the Rio Grande rift. Heating (~1.6 by BP) miles released in the 1883 Krakatoa and stretching of the crust in this eruption). The enormous ash clouds region led to the formation of this tear Generalized stratigraphy of the Quebradas region. Adapted from A Geologic Time from these eruptions circled the earth, in the earth’s crust. The rift is bounded Scale 2004, published by Cambridge University Press. affected global climates, and may have by uplifted mountains on its flanks, altered ocean chemistry. including the ones you see from this

2 3 Major boundary faults, detail at Stop 2. Reddish outcrops to the large uplifts, and deep north and west (as well as the deposits on STOP 2 S basins characterize the which you are standing) are poorly con- Abo Redbeds S Rio Grande rift. The main solidated Upper Tertiary and Quaternary T boundary fault along this sands and conglomerates of the Santa Mile: 4.0 T O part of the rift is on the west Fe Group. They represent materials Coordinates: N 34°06.940’ O side of the valley, along the eroded mainly from the Pennsylvanian W 106°48.545’ P face of Socorro Peak. The and Permian rocks in this area but include UTM: Zone 13, 333152E P main fault on the east side some interlayered volcanic rocks. 3776460N of the valley is just a few To the east and south you can see that hundred feet east of where some of the Pennsylvanian and Permian 1 you’re standing. These outcrops are tilted to a near-vertical 2 boundary faults control the orientation; in other places they are nearly position and width of the horizontal. This is a reflection of the -re Walk toward the southwest a few dozen The lens-shaped, lighter-colored at the base of this cliff valley. Unlike most valleys, peated episodes of folding and faulting that yards to the viewing area located at a is a phylloid algal mound in Madera Group south of this one was not cut by have affected this area. Some of the faults solitary fence post on a small ridge. You Stop 1. Note the lateral transition of the mound into darker, thin- are standing on the Lower Permian Abo ner limestones to the right. the river, but was formed are related to the formation of the rift; by tectonic processes and others are associated with earlier episodes, Formation. As you look down the small location and the Sandia and Manzano is merely occupied by the especially the Ancestral Rockies event arroyo, more exposures of red Abo sand- Mountains near Albuquerque. The rift Rio Grande (which has done some minor in Late Pennsylvanian to Early Permian stones, siltstones, and shales are visible. At is a complex of down-faulted blocks of downcutting). The rift has been the site of time. Prominent bands of gray limestone the far end of the arroyo, one can see the crystalline and pre-Tertiary sedimenta- substantial sediment deposition during its outcrops are visible to the east-southeast. gray limestones of the Upper Pennsylva- ry rocks overlain by sedimentary basin history, but the amount of sediment varies These reflect cycles of sedimentation, nian Madera Group. fills. Some of the basins have dropped along the length of the rift because of discussed at the next stop. During the Pennsylvanian–Permian more than two miles relative to the sur- differential subsidence from place to place. If you walk southeast from the base interval North America drifted north- rounding mountains. Rifting began 30 The deep basins contain many thousands of the hill and follow the vertical beds ward from a near-equatorial position in million years ago, and major sediment of feet of fill, some of it in the form of to the ridge crest to the south, you can mid-Pennsylvanian time to a position filling of the rift took place during the porous sands and gravels that constitute find well-bedded marine limestones that roughly 15 degrees north of the equator past 20 million years. The Rio Grande the drinking water aquifers for most of the were deposited in a shallow sea that once by Late Permian time. The drift of the has flowed through this area for about state’s population. covered the region. Locally, you can find continent through major climate zones, 5 million years, but only during the Rocks of Pennsylvanian–Permian mounds formed by phylloid (platy or coupled with the rain-shadow effects of past million years has the Rio Grande age can be seen to the south, southeast, leaf-like) algae, reef-like buildups that rising mountain belts, led to substan- become a through-going river that flows and east. Pennsylvanian strata are are typical of this time period. , tial changes in the types of sediments all the way to the Gulf of Mexico. Since predominantly gray outcrops consisting , bryozoans, fusulinid formed during that time. In particular, turning onto the byway, you have been of alternating beds of well-exposed foraminifers, and other marine fossils are Pennsylvanian rocks formed under mainly in reddish sandy and conglom- limestones and softer, less well-exposed common in these rocks. relatively humid conditions and Perm- eratic sediments of shales of the Upper Pennsylvanian Madera As you drive the 1.3 miles to Stop 2, ian rocks formed under conditions of – age, which were Group (310–300 m.y. b.p.). The reddish you will pass through red beds of Lower ever-increasing aridity. transported by small side streams and rocks visible to the east and northeast are Permian Abo Formation and some A third influence on these rocks alluvial fan channels from high areas on sandstones and shales of the Permian Abo basal Yeso Formation strata. came from global climate change and the east flank of the rift. Formation, which will be seen in more large-scale sea-level fluctuations. Late Socorro Peak Magdalena Mts. Strawberry Peak Chupadera Mts.

4 5 Pennsylvanian–Early Permian time Corners, NM). Examination of the Abo see near the base of salt). Some of was one of the earth’s major “icehouse” redbeds shows that they are mainly the outcrop a thick, those light-colored S climate intervals, with widespread con- of terrestrial (nonmarine) origin. The lens-shaped sand layers can be seen S tinental glaciations in the then-adjacent red color of these rocks results from body surrounded in the distance T southern parts of South America and the presence of small amounts (less by darker red up the arroyo to T O Africa as well as all of Antarctica. As than one percent) of iron in the form of shales. The sand the north of this O during the more recent Pleistocene hematite. Hematite (Fe2O3) is the same body is the filling stop. The upper P glaciations, Pennsylvanian–Permian mineral that gives the planet Mars its of a Permian river part of the Yeso P glaciers waxed and waned repeatedly, red color, and it forms by precipitation channel; the shale Formation also locking up more or less water on land or alteration in oxidizing environments. represents overbank includes massive and consequently causing worldwide The small, circular white spots (known or floodplain depos- gypsum and 2 sea levels to fall and rise. During the as reduction spots) that are common in its. Near the top of anhydrite beds. 2 last modern deglaciation, starting these strata show what the rock looks the outcrop, you can These progressive about 12,000 years ago, global sea see angled layers changes in the levels rose approximately 400 feet. (cross-stratification) rock section Recent studies have shown a compa- within individual reflect ever greater rable scale of sea-level changes (about sand beds; this is aridity as glaciers 260 feet) in Upper Pennsylvanian evidence of shifting disappeared, strata of New Mexico, and more than sand bars, again Global continental reconstructions that show the global climates twenty such sea level changes have been in a river system. northward shift of New Mexico from Pennsylva- warmed, and New recorded in rocks of that time interval. The bedding nian to Permian time. Mexico drifted The intensity of Southern Hemisphere surfaces of many of northward away glaciations decreased through Permian the sandstones have ripple marks and from the equatorial rainforest belt and time and probably ended at some point mud cracks; more rarely one can find into the world’s desert latitudes. in the Late Permian. Paleogeographic reconstruction of the western raindrop impressions. The fossils in What evidence of this do we see in U.S. in mid-Pennsylvanian time. The Quebradas these deposits include abundant plant the rocks of the Quebradas? The cyclic then was located in the basin off the western remains (leaf and stem impressions ledges of marine Pennsylvanian lime- flank of the Ancestral Rocky Mountains. and scarcer petrified wood, mainly stones alternating with more poorly from conifers and pteridosperms) and, exposed shales (visible in the distance in other areas, the fossilized tracks of at Stop 1 and here) reflect the glacially four-footed vertebrate land animals and driven rises and falls of sea level of that bones of lungfish. These all indicate period. During high sea-level intervals, that in this area Abo deposition took marine limestones were deposited in place in a river and floodplain system the shallow seas that occupied shelf with at least enough moisture in some areas; low sea levels led to retreat of the seasons to supply ephemeral streams seas, with increased erosion of nearby and grow plants. Such a semi-arid Channel sandstones west-southwest of Stop 2. Two major channels are bracketed with black uplifts and basinal deposition of sand- terrestrial setting is different from that bars. stones and shales. of the marine Madera limestones of the At this stop we see mainly strata Paleogeographic reconstruction of the western Late Pennsylvanian, and is different as As you drive the 4.1 miles to the next of the Lower Permian Abo Forma- U.S. in early Permian time. The Ancestral Rock- well from the more arid environments ies uplifts in New Mexico had been largely stop, you will pass both Lower Permian tion (299–284 m.y. b.p.). The red, eroded by this time and the intervening basins seen in younger, post-Abo Permian (generally reddish) and Upper Pennsyl- feldspar-rich shales, siltstones, and were filled with detritus from that erosion. strata. vanian (generally gray) rock outcrops lenticular sandstones are approximately The rock unit that directly overlies with some mid-Permian deposits 650 feet thick in this area. They were like where it is not as strongly oxidized the Abo is the Yeso Formation (yeso visible in the far distance on the high derived from Ancestral Rockies uplifts (probably because of the presence of means “gypsum” in Spanish). The lower ridgeline to the east. (especially the Pedernal massif, small organic matter). part of the Yeso has thin gypsum beds remnants of which can still be seen Looking across the valley at the small and thinner white layers that were once in the Pedernal Hills, south of Clines cliff (which is on private land), you can rich in halite (sodium chloride or table

6 7 chemically unstable feldspars, indicate you reach the fence line, look STOP 3 that Bursum sediments were derived at the limestone outcrops S Bursum Sandstones quite locally from the erosion of uplifted on the northeast side of the S blocks of the granite-cored Ancestral arroyo. Several prominent, T & Madera Lime- Rockies. The erosional unconfor- nearly black, irregularly lami- T O stones mity found in most areas between the nated rock layers again mark O Bursum and Abo Formations, the rapid multiple paleosol zones, which P Mile: 8.1 lateral changes in Bursum lithologies, are a feature of the uppermost P Coordinates: N 34°04.576’ and the derivation of Bursum strata Madera strata in this area. W 106°46.877’ from granitic uplifts indicates that During the 1.6-mile drive UTM: Zone 13 Bursum sedimentation coincided with to the next stop you will climb 3 an active phase of Ancestral Rockies the stratigraphic section 3 335640E 3772040N mountain building. from the purple uppermost If you cross back to the parking Pennsylvanian Bursum depos- This stop shows the deposits that area and walk west-northwest down Phylloid algal limestone from the Madera Group. The small, its, through the basal Permian directly underlie the Abo Formation in the small arroyo, you can see both the dark gray fragments are broken pieces of phylloid (leaf-like) Abo redbeds (seen at Stop 2), this region. The parking area is located Bursum–Madera contact and the lime- green algal shrubs. and into variegated (red and atop the Bursum Formation, of latest stones of the upper part of the Madera tan or white) sandstones and Continuing down the arroyo, the Pennsylvania age (299–284 m.y. b.p.) Group. The basal maroon shales of shales of the lower Yeso Formation low outcrops of Madera Limestone get in this area. Walk to the low outcrops the Bursum strata are in sharp contact (Meseta Blanca Member) for the final richer in marine fossils. Small fragments on the east side of the road for a better with a gray, rubbly, nodular, somewhat mile of the drive. of phylloid algae still dominate the as- look at the Bursum. The unit consists brecciated limestone at the top of the semblage here, but scarcer of deep violet-to-greenish shales, Madera Group. This limestone, termed fragments (“sea lilies,” members arkosic sandstones, and conglomerates. the , contains of the phylum Echinodermata), Multiple thin layers of calcareous many small, irregularly curved, platy brachiopods, and small fusulinids nodules representing discrete soil zones fragments that are the altered remains (extinct, single-celled marine are found at nearby localities (including of phylloid algae, leaf-like or cup- protozoans that look like tiny outcrops between Stops 2 and 3). Much shaped, inch-scale, green algal shrubs. cigars) are also present. Long, of the sediment in this area is probably Those leafy plates typically produce a thin, irregularly spaced, wavy of nonmarine origin, although marine texture that looks like a collection of bands of darker rock and thin, limestone and shale layers are present small, broken corn flakes. These small elongate cavities are common; in the Bursum at some localities in plants grew in enormous numbers in these are weathered stylolites, the Quebradas and at many localities the warm, shallow, equatorial seas of zones along which the rock has farther south. The Bursum Formation, the Pennsylvanian and early Permian. dissolved due to the pressure of approximately 600 feet thick in this In some places phylloid algae formed overlying deposits. A bit farther area, represents a transition between bioherms (essentially small reefs), some down-canyon, there are irregu- the underlying, predominantly marine of which now act as oil and gas reser- larly shaped, white-to-reddish Madera Group and the overlying, fully voirs in the subsurface. Laminated, irregular black crusts in Madera limestone. nodules of chert that stand out in terrestrial Abo Formation. A number of wispy, irregularly These have been interpreted as fossil soil zones. relief from the Madera limestone East of the road one can see Bursum laminated black crusts within these matrix. Chert is a very finely outcrops that include sandstone and limestones mark paleosols (fossil soil crystalline form of quartz that conglomerate beds with internal horizons). These paleosols formed di- forms as a replacement of patches of crossbedding and lenticular, channel- rectly on marine limestones, indicating limestone or of individual fossils. You shaped geometries. These coarse- abrupt exposure and repeated sea-level then cross a small fault that has dropped grained deposits contain angular quartz changes that reflect either waxing the Bursum–Madera contact back down and abundant pink feldspar grains. They and waning of Southern Hemisphere to creek level. After passing across some look much like granites, and the absence glaciers or, in this highly active tectonic Bursum sandstone beds, you will again of rounding of the grains, coupled with belt, localized uplift and subsidence of be in gray Madera limestone. Just before the abundance of physically weak and the seafloor (or both).

8 9 folding has rotated them to a vertical The formation of halite crystals (and Stop 4 orientation, producing what is often their preservation long enough to form S Lower Yeso called “tombstone topography.” These casts) requires sustained periods of low S sandstones are finer grained, have more humidity and thus indicates times of T Evaporitic Sand- rounded grains, and contain much less substantial aridity. The redder shale T O stones and Shales feldspar and more quartz than the older intervals have fewer halite casts and O Bursum and Abo sandstones seen at the probably reflect wetter cycles. Such P Mile: 9.7 last two stops. This reflects the fact that climate cycles apparently paralleled P Coordinates: N 34°03.325’ most of the Ancestral Rockies uplifts in cycles of glacial advance and retreat this region had been deeply eroded or (and global sea level fall and rise). W 106°46.483’ were buried under their own detritus The presence of limestone beds 4 UTM: Zone 13 by Yeso time. Thus, younger sediments (see exposures close to the west side 4 336205E 3769720N had to be transported ever longer of the road on the north side of the distances to reach this area, which Folded siltstones and shales of the Meseta arroyo), some with fragments of fossils, Here in the upper reaches of Arroyo del is reflected in increased abrasional Blanca Member of the Yeso Formation north- indicates that this section was depos- Tajo is an excellent place to see both the rounding of grains and destruction of west of Stop 4. ited in a nearshore marine setting with structural geology and sedimentology of associated faulting, and the axis of the both marine and terrestrial influences. the Quebradas. The beds on either side fold nearly parallels the road. Looking Halite casts and fossil fragments of the road are from the Meseta Blanca north or south you can see upended are typical of the kinds of relatively Member of the Yeso Formation. This is strata with sharp transitions from subtle evidence geologists must find in the lowest of four members (from base vertical to horizontal orientations. In order to decipher past environments. to top: the Meseta Blanca, Torres, Cañas some places, the strata are upside down. It is very much like the collection of Gypsum, and Joyita Members) in the This deformation obviously postdates evidence by forensic teams at a crime Yeso Formation, which is Early Permian deposition of the Permian rocks in this scene, and part of what makes geology in age. The Meseta Blanca Member area and, because it involves compres- such an interesting field. (mapped in this area as the lower Yeso sive forces that are not common during Formation) has a maximum thickness rifting events, it is likely that the folding of 300 feet in this region. The full Yeso is a product of the Laramide orogeny of Formation is roughly 1,000 feet thick Folded sandstones in the Meseta Blanca Member early Tertiary age. in the Quebradas, although it gets far of the Yeso Formation southeast of Stop 4. The If you walk back to the west side thicker in some nearby locations (to the rocks in the foreground are standing on end—a of the road and down into Arroyo del east, in the subsurface near Carrizozo, it classic example of “tombstone topography.” Tajo, you can examine some of the exceeds 4,000 feet in thickness). finer-grained beds of the Meseta Blanca The Meseta Blanca Member is one of unstable minerals such as feldspar. The Member. The stream-level outcrops the most distinctive units in the Quebra- change in character of the sandstones show distinct bands of orange-red and das. It is marked by cyclic color banding also reflects increasing aridity with white siltstones and shales that may re- of yellow to reddish-brown quartzose more long-distance wind transport (as flect Permian climate cycles. The white, to sub-arkosic sandstones as well as indicated by frosting on the quartz calcareous, silty shales once contained orange-red, gray and white siltstones, grains in the Yeso), coupled with more extensive halite (sodium chloride) as Salt casts in the Meseta Blanca Member of the shales, and calcareous shales. Compared marine influence and coastal deposition revealed by the presence of abundant Yeso Formation. to the underlying Abo Formation, the in this area. The Yeso deposits in the casts of former crystals (now dissolved, Meseta Blanca has a higher percentage Quebradas region generally represent During the very short 0.3-mile drive leaving behind sediment-filled crystal of sandstone, has more uniform (less a transition from marine to nonmarine to the next stop you will stay in Meseta outlines). You can see these character- lenticular) bedding, and has more of environments in restricted, coastal to Blanca deposits with views of younger istic casts by looking on the bedding an orange-red color compared with near-coastal settings dominated by sand strata to the east and older units to the surfaces of the very thin, platy, beds that the deep red of the Abo strata or the dunes and salt pans. west. make up the white layers. The crystals maroon color of the Bursum Formation. The structural deformation of these appear in raised relief as cubic forms, The sandstone beds are easily seen rocks is striking. A major fold affects some with sunken sides (commonly on the east side of the road where the rocks here, perhaps with some termed hopper crystals). 10 11 required light for growth). The more clearly recognizable throughout New STOP 5 recessive nodular limestones and black Mexico and adjoining states. However, Stop 6 S Pennsylvanian shales were probably deposited in some- isolating the relative influence of these Geologic S what deeper waters, and there are soil two processes on development of marine T Depositional Cycles crusts and red shales in the section that depositional cycles typically is not Panoramas T O Mile: 10.0 reflect episodes of exposure and and/or possible, given the limited stratigraphic Mile: 11.3 O Coordinates: N 34°03.051’ nonmarine sedimentation. control we have at this time. Coordinates: N 34°02.048’ P There are at least two major factors The 1.3-mile drive to the next stop P W 106°46.542’ (at the cairn) that could have brought about such will take you initially into the upper W 106°46.736’ UTM: Zone 13 changes in environmental conditions. Yeso Formation (mainly the Torres UTM: Zone 13 336106E 3769220N Local and regional tectonic move- Member), which includes some promi- 335775E 3767370N 5 ments can raise or lower the seafloor. nent gray limestone beds, commonly 6 Alternatively, worldwide sea-level marked by an abundance of ocotillo, This stop provides a chance to see at fluctuations of 250 feet or more have which thrive on alkaline soils that form This stop provides interesting panora- a distance depositional cycles within been documented as having occurred in on the gypsum-bearing limestones. mas in all directions. If you walk toward the upper part of the Madera Group. the Pennsylvanian due to growth and The high cliffs to the east expose the south to the mesa edge, you can The view to the west shows rocks shrinkage of Southern Hemisphere younger strata including the upper look down into Arroyo de las Cañas exposed in and near Arroyo del Tajo. ice masses (termed glacio-eustacy) two units of the Yeso Formation (the and view the panorama to the south and In the foreground are the orange-red, discussed at Stop 2. Cañas Gypsum and Joyita Members), southwest. Water flow from permanent gray, and white beds of the Meseta In the Quebradas it is likely that both the Glorieta Sandstone, and the San springs in the canyon keeps the area Blanca Member of the Yeso Formation tectonic and glacio-eustatic mechanisms Andres Formation. The last stage takes moist and allows for remarkably lush (discussed in detail at Stop 4). produced or influenced Madera cycles. you to a mesa top consisting of a thin vegetation and excellent cattle grazing Somewhat farther away are the deeper Glacio-eustatic sea-level changes are, by veneer of geologically young (less than 5 (the valley is a privately owned inhold- red siltstones and sandstones of the definition, reflected everywhere in the million year old) Pliocene–Pleistocene ing within BLM lands for that reason). Abo Formation (discussed at Stop 2). world’s oceans, and local and regional mountain-front or piedmont sands and The rocks exposed in the canyon walls Finally, on the far ridge, the gray lime- pulses of Pennsylvanian–Early Permian conglomerates sitting on limestones consist entirely of Yeso Formation, stones of the upper part of the Madera mountain building (including both of the Torres Member of the Yeso with gray and yellow limestones and Group (the Atrasado Formation, dis- uplift and subsidence of landmasses) are Formation. sandstones of the Torres Member in cussed at Stop 3) are well exposed. The gray Atrasado Formation Magdalena Mts. Sierra Chupadera Mts. South Baldy limestones of the upper Madera Group, de la San Mateo Mts. visible to the west of the road at this Campana Fra Cristobal Mts. site, show a very prominent bedding cyclicity. The rocks were folded and thrust faulted during the Laramide orogeny in the early Tertiary and are now standing nearly on end (see cover photo). The vertical beds have Top: Panorama looking south to west from Stop 6, showing reddish Permian rocks in the Arroyo de las Cañas (left) and pediments of young piedmont sands and gravels. Bottom: Panorama looking west to northwest from Stop 6, showing pediments of young piedmont sands and gravels (left and center foreground) with some Pennsylva- been eroded so that the hard, erosion- nian and Permian rocks exposed at the right. resistant limestone units are stand- ing out in relief; intervening nodular limestones and shales are less resistant Socorro Strawberry to erosion and form lower, soil- and Sierra Ladrones vegetation-covered intervals. In general, Peak Peak Polvadera Peak the prominent gray limestone ledges consist of shallow marine limestones (deposited in water depths that were probably 50 feet or less, based on the abundance of phylloid algae, which 12 13 upstream areas (to the southeast) and in more detail by walking downhill a long exposure of reddish sandstones STOP 7 into the arroyo. Although the Torres S and shales of the underlying Meseta Upper Yeso Carbon- Member here consists of sandstones, S Blanca Member directly to the south evaporites, and limestones, limestones T and southwest. The section has un- ate and Evaporite dominate these exposures. Most are fine T O dergone extensive folding and faulting Deposits grained and nearly featureless, although O which accounts for the variable orien- some layers are fossiliferous or contain P tations of beds. The mesa top directly Mile: 12.2 laminations and clasts of carbonate P to the south and southeast has modern Coordinates: N 34°01.938’ mud. In some zones, the calcite dunes of loose sand, blown up against W 106°45.957’ (CaCO3) of the limestones has been the eastern hills by the predominantly replaced by dolomite [(Ca,Mg)CO ] 6 UTM: Zone 13, 336106E 3 7 westerly winds. The eastern hills here, or chert (SiO2). In places, the rocks as at both previous and subsequent 3769220N are contorted or intricately fractured stops, consist of the upper Yeso, Glori- (forming boxwork fabrics), or contain eta, and San Andres Formations. In the valley below and toward the coarse breccia (rubble) layers and The panorama from the northwest north are excellent exposures of lenses. These structures may be caused to the north provides views of the rocks limestones and sandstones of the by normal tectonic events, but more seen at Stops 2 through 5, with gray Torres Member of the Yeso Formation. commonly such features are associated Oncolites, some with visible fossils as their cores, Pennsylvanian Madera Group lime- Overlying that unit are massive gypsum with sliding of rigid units on evaporite in Torres Member limestone (Yeso Formation). stones in the background and faulted, deposits of the Cañas Member of the beds that behaved plastically, or the col- during more recent uplift. red and yellow Abo to Yeso strata Yeso Formation, which is well exposed lapse of hard and brittle limestone and Most of the limestone layers in the in the foreground. Finally, the view in the low, rounded, whitish hills that sandstone beds where near-surface dis- Torres Member contain few or no toward the east shows high cliffs of line the south side of the (upstream) solution of underlying layers of highly visible fossils. A few layers, however, younger Permian rocks, including the part of the Arroyo de las Cañas. Farther soluble evaporites (anhydrite, gypsum have fragments of gastropods (snails), upper Yeso, Glorieta, and San Andres east, in the higher hills, yellowish and and halite) occurred. The Torres beds bivalves (clams), and rare cephalopods. Formations, which will be discussed reddish sandstones mark the highest not only contain collapse breccias, they Most such layers, including ones just further at Stop 7. This remarkable unit of the Yeso Formation, the Joyita also show molds of nodules and crystals downslope from the parking area, 360° panorama displays almost all the Sandstone Member. Above that lies a of gypsum and anhydrite. The overlying contain large numbers of only one or geologic units exposed in this region. white-to-pale-yellow, roughly 200-foot- unit, the Cañas Gypsum Member, two species of organisms and contain The mesa on which you are standing thick section of quartzose sandstones still contains massive gypsum at this microbially-coated grains, termed is formed of a veneer of Pliocene– of the Glorieta Formation. Finally, the locality, despite significant exposure and oncolites. The oncolites are roughly Pleistocene piedmont sands and gravels hills are capped with dark limestones, alteration. 0.5–2 inches in diameter, have many that overlie a thick, fine-grained, dolostones, evaporites, and sandstones The limestone outcrops along the irregular concentric coatings of calcium relatively featureless, gray limestone of the San Andres Formation. This sec- streambed north and northeast of the carbonate, and commonly have a fossil in the Torres Member of the Yeso tion includes some of the most prolific parking area show many of the features fragment at their core. Please refrain Formation. Many eroded pieces of the oil-producing strata in the Permian mentioned above. The beds have from collecting samples so others can limestone are visible on the surface of Basin of southeastern New Mexico and large-scale undulations and contain see these features as well. the mesa, and outcrops can be found west Texas. The San Andres (along with lens-shaped patches of coarse breccia Limestone beds such as these, with along the mesa margins. the overlying Grayburg interval) had with angular limestone blocks. The large numbers of only a few species The 0.9-mile drive to the next yielded more than 1.7 billion barrels breccia lenses are bounded by bedded of organisms, or beds that contain stop takes you across the mesa-top of oil and 1.9 trillion cubic feet of gas limestone and probably are related to mainly salinity-tolerant groups such piedmont deposits and then back through 2000 in southeastern New cave dissolution in underlying evaporite as bivalves, gastropods and microbes, into the upper Yeso Formation (the Mexico alone—roughly 36 percent of beds with localized collapse of the are interpreted as evidence for Torres and Cañas Gypsum Members). New Mexico’s total oil production and brittle limestones that formed the roofs deposition in a restricted, hypersaline As before, the high cliffs to the east 6 percent of its gas production. The of the caves. Some of the dissolution coastal embayment. Further evidence expose younger strata including the Yeso–Glorieta interval has produced an of evaporite and collapse of associated for hypersalinity comes from the Joyita Member of the Yeso Formation, additional 430 million barrels of oil and limestones may have taken place during abundance of calcite-lined cavities, the Glorieta Sandstone, and the San 3.4 trillion cubic feet of natural gas. humid climate cycles in the Permian. the solution-collapse breccias, and Andres Formation. You can look at some of these units Much of it, however, likely happened the boxwork fracture fabrics that all 14 15 are related to former evaporites. The quarter of an inch thick. The dark layers goes as low in the section as the Abo tograph. One set of faults are nearly marginal marine embayment in this consist of limestone and organic matter. Formation. As before, the high cliffs to parallel to the bedding planes; these S area probably was directly connected The light layers contain mainly gypsum. the west expose younger Permian strata are thrust faults indicating compres- S to more normal marine environments Such repeated cycles are interpreted as including the upper members of the Yeso sional stresses. The fold is termed a T known to exist in regions to the south representing varves —annual cycles with Formation, the Glorieta Sandstone, and fault-propagation fold because it is the T O and southeast of the Quebradas. dry-season evaporation producing gyp- the San Andres Formation. sliding of rocks along the thrust fault O A short and easy walk upstream sum and cooler, wetter seasons yielding that caused associated strata to buckle P along the east-west oriented section of organic limestone layers. The laminated and fold near the tip of the fault. The P Arroyo de las Cañas will bring you to deposits are indicative of a large and Stop 8 former presence of evaporite layers in superb exposures of the Cañas Gypsum relatively deep-water saline coastal lake Structural these rocks (before they were dissolved) Member of the Yeso Formation. After (salina) or restricted marine embayment may have contributed to the abundance 7 crossing a yellow sandstone bed that that extended 110 miles from just north Deformation of small thrusts by providing planes of 8 of Mountainair to south of Alamogordo easy sliding. and Truth or Consequences. Mile: 16.1 The thrust faults and related folds The other structures visible in the Coordinates: N 33°59.033’ in this area are generally interpreted to Cañas Gypsum mainly reflect alteration W 106°45.721’ have formed during the Laramide orog- produced during 270 million years UTM: Zone 13 eny (early Tertiary), a time when what of burial and subsequent uplift and 337148E 3761770N is now the Socorro Basin in the Rio exposure. Greenish clayey and silty Grande rift was a high-standing area. zones are insoluble material left behind The later inversion of this highland by dissolution of more soluble layers. We are now in slightly older rocks: the into a basin, through the extensional Nodular zones are especially widespread two lowest members of the Yeso Forma- tectonics that led to rift formation, and probably formed during cycles of tion (the Meseta Blanca Member over- produced a second set of faults that cut conversion of gypsum to anhydrite and lain by the Torres Member). The main the rocks at a high angle. At least one back to gypsum. Other intervals show rock types exposed here are red and of these high-angle normal faults can Contorted gypsum-limestone laminations yellow sandstones (varves) within the Cañas Gypsum Member of small-scale folds within laminated the Yeso at Stop 7. evaporites and more rarely include and siltstones and structures that look like wisps or gray limestones and marks the top of the Torres, the next tongues of flame; both probably result dolomites; evaporite several hundred yards of exposure on from flow (plastic deformation) within layers probably once the south side of the valley consist of the evaporite masses. That property of were interspersed, massive gypsum (the hydrated form plastic flow of evaporites (similar to the but were dissolved behavior of Silly Putty or taffy) can be during exposure of of calcium sulfate, CaSO4 · 6H2O). In most climates, gypsum is removed quite important. For example, evaporite these strata. through dissolution by near-surface deposits very similar to these are This location ground water. In the warm, dry climate widespread in the Delaware Basin south provides an excellent of New Mexico, however, gypsum can and east of Carlsbad. Those deposits now opportunity to see reach the surface and survive there host the WIPP site (the Waste Isolation some of the complex, for some time. This is an exceptional Pilot Plant), the only active underground multi-generational outcrop, and it is one of only a handful nuclear waste repository in the U.S. The structural features of places in the U.S. that such fresh reason for choosing that unit for waste of this region. Walk gypsum outcrops can be seen. disposal is because the evaporite deposits, south to the edge of Fault-propogation fold in the Yeso Formation at Stop 8. Several gen- The Cañas Gypsum Member in this in time, flow in around the wastes and the arroyo. In the erations of faults are visible, including low-angle compressional faults heal any fractures in the rock, forming a rock cliff on the far (marked in yellow), probably of Laramide age, cut by a high-angle normal area can be as much as 190 feet thick, fault (marked in red), probably of late Tertiary age. although at this site only 30–40 feet largely impermeable seal. side of the arroyo a single large fold of gypsum is exposed. The gypsum The 3.9-mile drive to the next stop be seen at this location. The normal displays a number of distinctive fabrics, takes you back through both the upper is immediately apparent. A number of associated faults are also visible, and faults consistently cut and offset the especially laminations of alternating and lower parts of the Yeso Formation thrust faults, allowing geologists to dark and light layers, an eighth to a and, in a few down-faulted areas, even their traces are marked on the pho-

16 17 confidently interpret that they must brown-to-maroon shales with interbed- Mountains and Socorro Peak in the far be younger than the thrusts. This is Stop 9 ded siltstones and sandstones. Small distance. S clear evidence of two tectonic events: Triassic Chinle lenses of conglomerate, again contain- As you proceed southward 3.1 miles the rocks were first squeezed in an east- ing clasts of Permian rocks, are present to the next stop, outcrops become sparse T west direction about 60 million years Group locally. The siltstones and sandstones and low but stay in Triassic strata. O ago during the Laramide orogeny, and Mile: 20.4 are laminated and crossbedded, with Eventually all outcrops disappear under- then were pulled apart during east-west Coordinates: N 33°57.340’ color contrasts between fresh maroon neath young, valley-fill sediments of P stretching associated with formation of or purple layers and slightly weathered, the northern Jornada del Muerto. The the Rio Grande rift during the past 30 W 106°43.720’ whiter bands. Widespread layers of fist- views from the road include a panorama million years. UTM: Zone 13 sized calcareous nodules indicate zones of mountains from the Oscura and San If you look toward the west down the 340269E 3758590N of Triassic soil formation. Andres ranges and the hills surround- 8 arroyo, more such folds and faults are The absence of marine fossils in ing the Cerro de la Campana in the visible. Toward the east you can see, as Chinle deposits (and the presence, in southeast and south, to the San Mateo, at Stops 3–7, the higher cliffs consist- We have left the Upper Paleozoic other areas, of extensive vertebrate Magdalena and Socorro Mountains to ing of upper Yeso, Glorieta, and San (Pennsylvanian and Permian) strata and remains), the occurrence of soil-formed the southwest and west-northwest. Andres strata. The yellowish quartzose are now in Lower Mesozoic (Trias- nodules and mudcracks, the abundance sandstones of the Glorieta are espe- sic; roughly 220 m.y. b.p.) deposits. of lenticular or channel-shaped bodies Stop 10 cially well exposed here. Although once classified as belonging of sandstone and conglomerate within S The 4.3-mile drive to the next stop to the Dockum Group, these rocks predominantly finer-grained shales, Southern takes you across mesa-top piedmont are now generally placed in the Chinle all provide evidence that these rocks Panorama T deposits and then back into underlying Group. formed along ancient river systems in Yeso and Abo Formations. As you get The isolated outcrops at this stop a continental environment. The shales Mile: 23.5 O to the lower part of the Abo section, show only a small portion of the roughly were deposited on broad floodplains, Coordinates: N 33°55.812’ massive ledges of gray Pennsylvanian whereas the crossbedded sandstones 500-foot maximum thickness of the full W 106°41.280’ P limestone outcrop to the west of the Triassic section in this region. Purple- and conglomerates reflect small, migrat- road. As before, the high cliffs to the to-nearly white (where weathered), ing channels and bars. The deep red- UTM: Zone 13 east expose the Joyita Member of the crossbedded, micaceous sandstones to-maroon color of the Triassic strata 343981E 3755700N 10 Yeso Formation, the Glorieta Sand- dominate the small cliffs west of the indicates deposition (or alteration) in stone, and the San Andres Formation. road. The bedding planes of some of the a semi-arid environment in which iron This stop provides a wonderful view of At approximately 1 mile before Stop 9, sandstones show mud cracks, and the minerals were strongly oxidized (as the region to the south: the broad plains the road passes very close to the promi- coarser, conglomeratic deposits have in the older Bursum, Abo, and Yeso of the northern part of the Jornada del nent yellow sandstones of the Glorieta fragments of shale, limestone, and older deposits). Muerto bordered by a series of moun- Formation and affords an opportunity red sandstone, presumably all derived From this stop, one also gets an excel- tain ranges. This desolate region, now (for those willing to do some hiking from erosion of Permian strata. Such lent view to the north of the youngest largely part of the White Sands Missile and climbing) to examine those rocks. erosion is not surprising, consider- of the Permian deposits in this area. Range, was the site of early Spanish ex- ing that there is a 30–40 million-year The long, light-colored cliffs expose at peditions northward from Mexico into time gap between the youngest of the their base the upper part of the Yeso central and northern New Mexico. The Permian and the oldest of the Triassic Formation; the middle zone of the cliffs mountains in the background include S strata found in this region. It may imply consists of the well-bedded, yellow (from southeast to south) the Oscura some uplift during that hiatus, which, sandstones of the Glorieta Formation; Mountains (with Mockingbird Gap at T through erosion of a variety of Permian and the upper parts of the cliffs consist the southern end), Capitol Peak, Sheep units, would have provided a source for of erosion-resistant beds of the San Mountain and , the more O these clasts. Andres Formation. A fault separates distant main part of the San Andres P East of the road one can examine less the younger (downthrown) reddish- Mountains. The Trinity site, location obvious but more extensive exposures of brown Triassic strata in the valley in of the world’s first atomic bomb test on the foreground from the older, uplifted July 16, 1945, lies on the plains just west Crossbedded siltstones and sandstones of the Permian rocks in the cliffs in the im- of the . 9 Triassic Chinle Group on the west side of the mediate background. Through gaps in road at Stop 9. those cliffs, one can see the Magdalena

18 19 These mountains all are tilted and Alamogordo, New Mexico. About the Author blocks, separated by half-graben The small sharp, distinctive peaks to S Peter Scholle is the state geologist for New Mexico and the director of the New Mexico Bureau of basins, formed by faulting during rift- the south-southwest include the Cerro Geology and Mineral Resources, a research and service division of New Mexico Tech in Socorro. T ing of the Basin and Range Province, de la Campana (which translates as “Hill Peter’s rich and diverse career has included nine years with the U.S. Geological Survey, many years which extends from the Guadal- of the Bell”). They look like a series of of working for and with the petroleum industry, seventeen years of university teaching, and eleven O upe and Sacramento Mountains of small volcanoes but, although they are years in state government. His specialty is carbonate sedimentology and diagenesis. He has published southeastern New Mexico westward composed of rocks of volcanic origin, the broadly and continues to find time for teaching, at New Mexico Tech and elsewhere. P for nearly 600 miles into southern peaks are not volcanic cones. These hills California. That entire region features are erosional remnants of once much Cover: View to the southwest from Stop 5 showing reddish Permian rocks (foreground) and cyclic landscapes similar to those visible from larger deposits of mid-Tertiary (30–35 bedding in Madera Group limestones (background). These strata have undergone Tertiary-age folding 10 this stop, with rugged, tilted, north- m.y. b.p.) volcaniclastic breccias and lava and thrust faulting, and the limestones now have a near-vertical orientation. south oriented mountain ranges, sepa- flows (along with some associated east- rated by flat-floored basins, with young west oriented dikes). They were derived sediment filling deep depressions. The from a stratovolcano that was centered A Geologic Guide to the Quebradas Back Country Byway province thus has a strong topographic to the west of the current outcrops and Copyright © 2010 New Mexico Bureau of Geology and Mineral Resources grain that makes north-south travel, now is probably mostly buried under the A division of New Mexico Institute of Mining and Technology 801 Leroy Place through elongate valleys, much easier Rio Grande basins. Socorro, NM 87801 than crossing multiple ranges while To the west of Cerro de la Campana http://geoinfo.nmt.edu journeying in an east-west direction. It are low hills largely composed of (575) 835-5490 is that grain that strongly influenced Cretaceous rocks, and in the farther Produced by the New Mexico Bureau of Geology and Mineral Resources routes of the conquistadors for more distance lies the Rio Grande valley in cooperation with the U.S. Bureau of Land Management.

Written by Peter A. Scholle Editing and Production: L. Greer Price and Gina D’Ambrosio Design, Layout, and Production: Gina D’Ambrosio Graphics: Peter A. Scholle and Phil Miller Cartographic Assistance: Jeremy Zimmerman Paleogeographic maps on page 6 courtesy of Ron Blakey Global reconstructions on page 7 modified from maps byC. R. Scotese, PALEOMAP Project Photos by the author Generalized cross section looking south in the vicinity of Stop 10. Note the extensive faulting on both sides of the Rio Grande. Distributed through: The U.S. Bureau of Land Management than 100 years and continues to affect with its western border ranges, the Socorro Field Office trade and transport to this day. San Mateo and Magdalena Mountains 901 South Highway 85 The mountain ranges visible to the and Socorro Peak. These mountains Socorro, NM 87801 www.blm.gov/nm/st/en/fo/Socorro_Field_Office.html east and south all contain rocks com- expose primarily volcanic rocks of mid- 575-835-0412 parable to those present in the Quebra- Tertiary age with subordinate Paleozoic das—predominantly Pennsylvanian sedimentary strata. The volcanic units, First Printing, 2010 and Permian sedimentary deposits with which extend westward into Arizona, Printed in New Mexico exposures of underlying Precambrian represent the edge of the Mogollon- basement rocks. They differ in that Datil volcanic field, which contained 20 Below: Panorama looking from east-southeast to west-southwest at Stop 10. The mountains to the they preserve remnants of Cambrian– or more enormous caldera complexes. east are the Oscura Range. To the south lie Mockingbird Gap and the . The tallest of the distinctive conical peaks at the right is the Cerro de la Campana. The Jornada del Muerto Ordovician, Devonian, and Mississip- During the roughly 12 million years of occupies the flat foreground of the entire vista. pian sedimentary strata. Cambrian-to- its main eruption history (36–24 m.y. Mississippian strata are well exposed b.p.), this was the place to be if you were and easily accessible in the Franklin into explosive and destructive volcanic Mountains (in and near El Paso, Texas) eruptions, some as much as to 1,000 and on the west side of the Sacramento times the magnitude of the 1980 Mount Mountains in the vicinity of Tularosa St. Helens eruption.

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