the surface water system. Snow melt in the high VOLCANIC STRATIGRAPHY OF THE WEST- mountains recharges shallow perched aquifers ERN SIERRA BLANCA VOLCANIC FIELD, Abstracts that discharge at springs that feed streams and SOUTH-CENTRAL NEW MEXICO, S. A. Kel- ponds where evaporation occurs. Water in ponds ley, [email protected], and D. J. Koning, and streams may then recharge another shallow New Mexico Bureau of Geology and Mineral perched aquifer, which again may discharge at a Resources, New Mexico Institute of Mining and spring at a lower elevation. This cycle may occur Technology, Socorro, New Mexico 87801; K. A. New Mexico Geological Society several times until the water is deep enough to be Kempter, 2623 Via Caballero del Norte, Santa Fe, spring meeting isolated from the surface water system. A deeper New Mexico 87505; K. E. Zeigler, Zeigler Geo- regional aquifer may exist in this area. East of logic Consulting, Albuquerque, New Mexico The New Mexico Geological Society annual Mayhill along the Pecos Slope, regional ground 87123; L. Peters, New Mexico Bureau of Geology spring meeting was held on April 16, 2010, at the water flow is dominantly to the east toward the and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mex- Macey Center, New Mexico Tech, Socorro. Fol- Roswell Artesian Basin. Some ground water also ico 87801; and F. Goff, Department of Earth and lowing are the abstracts from all sessions given flows to the southeast toward the Salt Basin and to the west into the Tularosa Basin. Planetary Sciences, University of New Mexico, at that meeting. Albuquerque, New Mexico 87131 Keynote presentation p. 60 SESSION 1—GEOLOGY OF THE SACRAMENTO A thick succession of trachyandesite, trachydacite, volcaniclastic sediments, and minor welded ash- Session 1—Geology of the Sacramento Mountains MOUNTAINS AND TULAROSA BASIN and Tularosa Basin p. 60 flow tuffs is preserved on three north-south-strik- Session 2—Spring microbes and caves p. 60 COMPARISON OF ALLUVIAL FAN GEO- ing fault blocks on the west side of Sierra Blanca. Session 3—Hydrogeology of the Sacramento MORPHOLOGY, SEDIMENTATION, AND The volcanic rocks on the eastern fault block, Mountains p. 61 EROSION ALONG THE EASTERN MARGIN which includes Sierra Blanca, are composed of Session 4—Paleontology p. 63 OF THE TULAROSA BASIN, NEW MEXICO, a basal thick (> 250 m) sequence of pyroxene- Session 5—Magmatism and volcanism p. 63 D. J. Koning, [email protected], New Mexico phyric trachyandesite breccia and debris-flow deposits overlain by a stack of plagioclase-phyric Session 6—Climate p. 64 Bureau of Geology and Mineral Resources, trachyandesite lava flows that are variably fine Session 7—Stratigraphy p. 64 New Mexico Institute of Mining and Technol- grained to crystal rich. The trachyandesite flows, Session 8—Hydrology p. 65 ogy, Socorro, New Mexico 87801 40 39 Poster sessions with published Ar/ Ar ages of 29.3–37.3 Ma, This study compares two sets of alluvial fans are among the oldest volcanic rocks in the area. Paleontology and stratigraphy p. 65 along the eastern margin of the Tularosa Basin. Volcaniclastic sediments are not common in the Granite and rock piles p. 68 Alluvial fans of the first set are gravelly and con- stacked lava flow section, but are preserved in Hydrogeology p. 69 tain both debris-flow and stream-flow sediment. paleochannels cut in the upper part of the plagio- Geophysics and structure p. 69 Fan-head trenching is confined adjacent to the clase-phyric trachyandesite. The volcanic rocks Alluvial fans and travertine deposits p. 70 mountain front. Fans belonging to the second set in the middle fault block between Sierra Blanca Geologic mapping and spatial archeology p. 71 are derived from large mountain front drainages and the Godfrey Hills are primarily the pyroxene- Author and subject indices p. 72 north of Alamogordo. These alluvial fans lack phyric trachyandesite breccia. debris-flow sediment, have less gravel and more The western fault block, including the Godfrey KEYNOTE clay, and exhibit entrenched, main-stem arroyos Hills, exposes the younger part of the volcanic suc- throughout their length. The longer arroyos per- cession of the Sierra Blanca volcanic field. The old- HYDROGEOLOGY OF THE SOUTHERN haps relate to their finer-grained sediment and est flows, found at low elevation on the south and SACRAMENTO MOUNTAINS, G. C. Rawl- higher discharges from their respective moun- west sides of the Godfrey Hills, are dark-colored, ing, [email protected], New Mexico Bureau of tain front canyons. porphyritic trachyandesite similar to the plagio- Geology and Mineral Resources–Albuquerque Both sets of alluvial fans experienced simi- clase-phyric trachyandesite on Sierra Blanca. Volca- Office, New Mexico Institute of Mining and lar erosional and depositional histories in niclastic channel fills are locally present between Technology, Albuquerque, New Mexico 87106 their proximal and medial areas. Erosion was these flows. The dark-colored porphyritic tra- The southern Sacramento Mountains are an impor- concentrated in arroyos during 18–8 ka, with chyandesite flows are thinner and the volcani- tant source of recharge to the lower Pecos Valley, pedogenesis occurring on surfaces between clastic sedimentary rocks are thicker toward the Roswell Artesian Basin, and Salt Basin aquifers. arroyos. Widespread aggradation occurred north end of the hills. The dark-colored flows are overlain by (1) a discontinuous fine-grained, flow- Significant declines in water levels in wells, spring between 8 and 3 ka on both sets of fans. On the banded trachyte, (2) a thick volcaniclastic interval and stream flow have occurred in the past 15 yrs. first set of alluvial fans, stream-flow sediment containing a few thin, discontinuous trachyandes- In response, the Otero Soil and Water Conserva- commonly transitions upward into debris-flow ite and trachydacite flows capped by a continu- tion District and the New Mexico Bureau of Geol- sediment, with an inset, coarse-grained deposit ous trachyandesite flow, (3) a welded ash-flow ogy and Mineral Resources (NMBGMR) initiated found below the debris flows. Stream-flow and clayey-sandy sheetflood deposits characterize tuff (Palisades tuff; 28.67± 0.05 Ma), (4) a sparsely a multi-scale study of the regional hydrogeology porphyritic trachyandesite with zones of breccia to delineate areas and timing of ground water the second set of alluvial fans between 8 and 3 ka. Coarse-grained channel-fill deposits inter- (28.59 ± 0.07 Ma), and (5) an upper fine-grained recharge, determine direction and rates of ground finger with clayey-silty, very fine to medium- trachyte. The Palisades tuff is thicker at the north water movement, and understand interactions grained sand. Fine-grained sediment is gener- end of the Godfrey Hills. In addition, a thin tuff between different aquifers and the ground water ally bioturbated, internally massive, and has (tuff of Bucky Pasture) is preserved in the volca- and surface water systems in the mountains. undergone weak pedogenesis. Pebbles in the niclastic interval in the northern Godfrey Hills. The Yeso Formation, which consists of layers of fine-grained sediment are scattered or in thin Thickness variations and the degree of welding limestone, dolomite, sandstone, and siltstone, is the to medium lenses. These observations indicate of the tuffs suggest the presence of an undetected primary aquifer in the study area. Fractured lime- an aggrading fan landscape during the middle local caldera northeast of the Godfrey Hills. stones and dolomites are the main source of water Holocene. Erosion occurred between 3 and 2 ka for most springs and wells in the southern Sacra- on both sets of alluvial fans. Another episode of SESSION 2—SpriNG MICROBES AND CAVES mento Mountains. Recharge primarily occurs in the aggradation occurred during 0.5–2.0 ka, which high mountains west of Mayhill, where the Yeso on the second fan set is marked by better strati- MICROBIAL RICHNESS AND DIVERSITY Formation is exposed at the surface. Stable isotope fication and slightly coarser texture than earlier IN CO2-RICH MOUND SPRINGS OF THE data suggest that snow melt usually contributes Holocene deposits. North of Alamogordo, there TIERRA AMARILLA ANTICLINE, NEW MEX- significantly more to ground water recharge than was eolian reworking of sediment and local- ICO, B. Cron, [email protected], and L. J. Crossey, summer precipitation. However, extreme summer ized, periodic arroyo formation and backfilling Department of Earth and Planetary Sciences, Uni- precipitation events, such as those that occurred during 0.5–2.0 ka. These observations indicate versity of New Mexico, Albuquerque, New Mex- in 2006 and 2008 do recharge the ground water that the late Holocene experienced episodes of ico 87131; D. E. Northup, Department of Biology, system, resulting in significant increases in water surface instability, perhaps due, at least in part, University of New Mexico, Albuquerque, New levels in wells and spring discharge. to sparser grass and low-lying shrubs. Pro- Mexico 87131; and K. E. Karlstrom, Department of The ground water system in the high moun- nounced erosion has occurred on the proximal Earth and Planetary Sciences, University of New tains west of Mayhill is characterized by several and medial parts of both alluvial fan sets dur- Mexico, Albuquerque, New Mexico 87131 fracture-controlled leaky perched aquifers that are ing the past 100–150 yrs, resulting in prevalent A series of mesothermal (~ 25° C) mound springs interconnected by regional fracture networks and gravel lag deposits and gully dissection. located along the Tierra Amarilla (TA) anticline are 60 NEW MEXICO GEOLO G Y May 2010, Volume 32, Number 2 related to a regional occurrence of CO2-rich traver- only B.P. 836 yrs, indicating an abrupt change 87801; G. C. Rawling, New Mexico Bureau of Geol- tine-depositing springs in north-central New Mex- in climatic or hydrochemical conditions within ogy and Mineral Resources–Albuquerque Office, ico.