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 Pennsylvanian, Permian, Late Cenozoic, and Quaternary The 24-mile-long road is dirt; a age. Triassic and Upper Cretaceous 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 Group 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 Mancos Shale 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 Jurassic 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 Magdalena Mountains (the massive Socorro–Magdalena region. From Moenkopi Formation 252 ridge forming the far skyline) and a series the 1870s to the early 1900s this area Lopingian 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 Glorieta Sandstone 0–400 Peak, Polvadera Peak in the Lemitar those mines are now closed, this Cisuralian 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 New Mexico Institute of Mining Abo Formation 230–1700 most of those ranges, but volcanic rocks and Technology (New Mexico Tech) in 299 make up most of the outcrops. Socorro. Bursum Formation 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 Sandia Formation 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 Mississippian regions in the world. Many individual from this stop as a narrow, green strip 354 Devonian 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 Silurian 443 the atmosphere. The largest eruptions the length of New Mexico from Ordovician yielded 240 cubic miles of such material Colorado to El Paso (Texas) and the 490 Cambrian (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 Precambrian 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 limestone 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 limestones 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.