include allowing growth to become dependent in the Taos region; an inventory and geochemi- on a continually shrinking supply, responsibility cal study of the springs in the Rio Grande gorge; Abstracts for the perpetual pumping, and commitment of a paleoseismic trenching study of the southern future energy resources. Sangre de Cristo fault near Taos; and a study of the geology, hydrogeology, and hydrogeochem- INVITED SPEAKERS istry of surface water/ground water interactions along the Rio Grande in northern Taos County. New Mexico Geological Society THE SAN LUIS BASIN OF THE NORTHERN The Taos Soil & Water Conservation District has spring meeting RIO GRANDE RIFT, P. W. Bauer, bauer@nmt. inventoried water wells and mapped the ground edu, New Mexico Bureau of Geology and water and water quality of the county. Over The New Mexico Geological Society annual Mineral Resources, New Mexico Institute of many years, Glorieta Geoscience, Inc., has inves- spring meeting was held on April 18, 2008, at Mining and Technology, Socorro, New Mexico tigated the hydrogeology, aquifer characteristics, Best Western Convention Center, Socorro. Fol- 87801 and hydrogeochemistry of the Taos region. lowing are the abstracts from all sessions given The San Luis Basin (SLB) is the northernmost at that meeting. large basin of the Rio Grande rift. It extends EVOLVING GEOLOGIC UNDERSTANDING about 240 km from Velarde, New Mexico, to OF THE ESPAÑOLA BASIN, RIO GRANDE Keynote presentation p. 52 Poncha Pass, Colorado, encompassing the San RIFT, NORTHERN NEW MEXICO, G. A. Invited speakers p. 52 Luis Valley to the north and the Taos Plateau to Smith, [email protected], Department of Earth Session 1—Rio Grande rift, San Luis and Española the south. The basin is bounded on the east by and Planetary Sciences, University of New Basins p. 53 the Sangre de Cristo Mountains, on the west by Mexico, Albuquerque, New Mexico 87131 Session 2—Stratigraphy, structure, and paleontology p. 55 the Brazos uplift and San Juan Mountains, and Session 3—Rio Grande rift, Albuquerque and southern on the south by the Picuris Mountains. Ranging The Española Basin is central to studies of the basins p. 57 from 30 to 70 km wide, with elevations between Rio Grande rift because it is home to the type Session 4—Hydrogeology and climate p. 59 about 7,000 and 8,000 ft, the basin is said to be Santa Fe Group—superb badland exposures Poster sessions the world’s largest high-elevation valley. It is of rift-basin fill rich in vertebrate faunas and Paleontology p. 60 nearly the size of the state of Connecticut and datable ash beds. New 1:24,000-scale geologic Stratigraphy, structure, and mapping p. 61 averages less than seven people per square mile. maps (mostly NMBGMR supported by USGS- Hydrology, hydrogeochemistry, climate, and The Rio Grande originates in the San Juan Moun- STATEMAP), aeromagnetic data (USGS), and microbiology p. 64 tains, flows through the valley to Alamosa, runs subsurface stratigraphic studies of the Pajarito Author and subject indices p. 66 south through a gap in the San Luis Hills, and Plateau (LANL) have enhanced geologic under- into New Mexico where it has carved the Rio standing over the last decade. Stratigraphic KEYNOTE Grande gorge. studies and lithofacies mapping by Dan Kon- The SLB is east-tilted, with about 8 km of Neo- ing build upon earlier interpretations by Ray IS A FEW BILLION ACRE-FEET OF STORED gene throw along the normal Sangre de Cristo Ingersoll to show that three primary sediment GROUND WATER REALLY A RESOURCE?, fault, and with a complex hinge zone along the sources filled the basin: erosion of granitic base- J. W. Shomaker, John Shomaker & Associates, western border. In the New Mexican portion of ment and Paleozoic rocks of the Santa Fe Range Albuquerque, New Mexico 87106 the basin, a deep north-south graben (the Taos on the east, recycling of volcaniclastic debris Many river-connected ground water basins store graben) exists along the Sangre de Cristo fault. along with quartzite-rich basement detritus large volumes of water that can’t be pumped The deepest part of the graben is west of Taos derived from the north, and recycling of volcani- and used because the resulting depletion of Pueblo, where the depth to Precambrian rocks clastic debris along with Paleozoic sedimentary the flow of the river would impair the rights is estimated to be >5,000 m. The west-bounding detritus that entered the basin from northeast. of downstream users. The Albuquerque–Belen fault of the Taos graben, known as the Gorge fault, This latter sediment pathway may relate to an Basin, for example, stores several hundred mil- approximately coincides with the Rio Grande ancestral Rio Embudo with headwaters far to the lion acre-feet, which might be compared with the gorge. West of the gorge, a bedrock bench rises east of the modern river, as suggested by upper recent (Year 2000) combined consumptive use of gently to the topographic basin boundary along Miocene basalt flows that probably entered the 184,000 acre-feet in Sandoval, Bernalillo, and the Tusas Mountains. To the north, the bench basin from the Ocate volcanic field. The Santa becomes a complex, intra-rift horst with pre-rift, Valencia Counties, but the Rio Grande is already Fe River also had a larger watershed in the past Oligocene volcanic rocks exposed in the middle of over-appropriated, and an increase in pumping that included the modern upper Pecos Valley. the rift at the San Luis Hills of southern Colorado. would cause still more depletion of the stream. This larger drainage produced coarse-grained, The 65-km-long, northeast-striking Embudo fault The Española and Lower Rio Grande Basins hydrologically important channel deposits rich is a transfer (or accommodation) zone that forms store hundreds of millions of acre-feet more. If in Paleozoic sedimentary detritus and quartzite the complex structural boundary that absorbs the the system is too large for channel-lining to be that covered a broad area of the southern basin differential extension between the east-tilted SLB during the Miocene. Beheading of the earlier practical, to isolate the river from the ground and the west-tilted Española Basin. water system, the stored ground water must Santa Fe River basin may have resulted from rise The southern part of the basin is a physio- of the Santa Fe Range as a ruptured hanging- simply remain in place. graphically and geologically unique terrain wall hinge zone uplift that paradoxically defines Another approach would be to pump the non- known as the Taos Plateau. The Pliocene to Pleis- higher elevations than the footwall region along renewable ground water, put to beneficial use tocene Taos Plateau volcanic field is the largest the western side of the Española Basin. Research only the portion that actually comes from stor- (7,000 sq km) and perhaps most compositionally in two areas implies that basin subsidence was age, and return the balance to the stream. As the diverse volcanic field in the rift, with at least 35 underway by Oligocene to early Miocene. Near cones of depression expand and eventually reach discrete vents that range from tholeiitic basalt Santa Fe, volcaniclastic strata of the Bishop’s equilibrium, the entire amount pumped would to rhyolite, and that form vent morphologies be at the expense of streamflow—but pumping including shield volcanoes, cinder cones, and Lodge Member of the Tesuque Formation cor- and delivery to the stream must continue for- volcanic domes. The plateau surface shows only relate to the Espinaso Formation and include ever so as to prevent the natural system from minor dissection, with the Rio Grande and its 30 Ma tephra. These deposits overlie ~400 m of replacing the volume withdrawn from storage. major tributaries confined to deep canyons. conglomerate derived from Paleozoic and Pre- Although it seems implausible, this situation is The SLB is host to a variety of recent and ongo- cambrian rocks and deposited on basement for- theoretically sustainable if the revenue derived ing geological work. Through the STATEMAP merly denuded during Laramide uplift. These from sale of the stored water has established a program, the NMBGMR has mapped all of the relationships indicate Oligocene foundering of perpetual fund to support the continued pump- 7.5-min quads in the southern SLB. The largest the earlier uplift. Within the Abiquiu embay- ing. One hypothetical system in the Rio Grande ongoing project is a USGS program designed to ment in the northwest part of the basin, pre-25 valley could provide a total of about 6.8 million assess the influence of geology on the availability Ma strata of the lowermost Santa Fe Group thin acre-feet for municipal use (with 50% return of ground water, natural resources, and hazards westward across a staircase of east-facing faults flow) over 100 yrs, at a cost less than large-scale in the central SLB. As part of this study, much to the rift margin. desalination. A very reliable understanding of of the basin was flown for a high-resolution the ground water regime, and the threshold of aeromagnetic survey. Other recent and ongoing subsidence problems due to excessive draw- NMBGMR projects include: a series of detailed A GEOLOGIC OUTLINE OF THE ALBU- down, would be vital. Public-policy implications hydrogeologic assessments of high-growth areas QUERQUE BASIN, S. D. Connell, connell@gis. 52 NEW MEXICO GEOLO G Y May 2008, Volume 30, Number 2 nmt.edu, New Mexico Bureau of Geology and a north- to northeast-tilted half graben whose recharge. 87Sr/86Sr varies from 0.7074 to 0.7156, Mineral Resources, Albuquerque Office, Albu- footwall was the Caballo Mountains.