John W. Hawley

Prehistoric agricultural terraces and soils in the Mimbres area, New Mexico

Abstract Soils at some prehistoric agricultural sites in New Mexico were investigated to study agricultural adaptation in a semi‐arid mountainous region, evaluate soil productivity, and determine long‐term effects of agriculture on the physical environment. The sites, farmed during the Mimbres Classic period (about AD 1000 to 1150), occur within certain geomorphic settings, implying a strategy to optimize climatic and hydrologic conditions for runoff agriculture. The landscape was modified by terracing, which probably served to reduce runoff velocity, increase soil moisture, and thicken the naturally thin A horizon. Comparisons of prehistoric agricultural soils with nearby, similarly developed, uncultivated soils indicate significant differences in soil properties over eight centuries after farming ceased. Soil changes resulting from the prehistoric agriculture were mostly degradative, including accelerated erosion, compaction, and reduced concentrations of nutrients such as nitrogen and phosphorus. Despi...

Use of radiometric (Cs-137, Pb-210), geomorphic, and stratigraphic techniques to date recent oxbow sediments in the Rio Puerco drainage Grants uranium region, New Mexico

In the absence of historic geochemical baseline data for the Grants uranium region, environmental changes resulting from uranium mine-mill activities can be determined only by indirect methods. A methodology for determining the age of recent sediments in streams draining the region has been established based on combined geomorphic, stratigraphic, and radiometric dating techniques. Because clayrich sediments retain possible radionuclides and heavy metals derived from mineralization and mined sources, sample sites which contain fine-grained deposits that both predate and postdate mine-mill activity were located in abandoned-channel segments (oxbows) of major streams draining the eastern Grants uranium region. Aerial photographs (and derivative maps) taken between 1935 and 1971 provided the historical and geomorphic documentation of approximate dates of oxbow formation and ages of alluvial fills in the abandoned-channel segments. Pits were dug at these oxbow sites to determine stratigraphy and composition of the deposits. Samples collected from pit walls and auger holes below the pits were subjected to radiometric analysis by gamma ray spectrometry for the artificial radionuclide Cs-137 and the natural radionuclide Pb-210 as well as other U-238 and Th-232 daughters. Because of the dynamic nature of the system, absolute dating with Cs-137 was not possible but samples could be dated as either pre-or post-1950. The 1950 date is important because it marked the beginning of the uranium exploitation in the region. The Pb-210 dating was not possible because background Pb-210 was very high relative to fallout Pb-210.

Early Contributions to Arid-Zone Hydrogeology in the Eastern Basin and Range Region

Introduction The Basin and Range (B&R) physiographic province of the American West has been the center of major advances in arid-zone hydrogeology since the Civil War, with contributions from many early giants of North American geology. Emphasis here is on evolution of geology-based conceptual models of intermontane basin, river valley, and mountain block aquifer systems in the eastern B&R region through 1945. This area includes the B&R Mexican Highland and Sacramento sections, much of the Rio Grande rift tectonic province, and parts of the upper Pecos and Gila River basins in New Mexico, Trans-Pecos Texas, and Arizona (Gile et al. 1981; Mace et al. 2001; Connell et al. 2005; Hawley 2005). It is also in or adjacent to Ground Water Region 7—Central Alluvial Basins as defined by Heath (1988) and described by Anderson et al. (1988). Our overview comprises a series of brief statements about pioneering contributions of individuals and institutions with strong regional ties, especially studies that focus on geologic (geomorphic, hydrostratigraphic, lithofacies, and structural) controls on ground water flow and hydrogeochemistry. The basic premise is that many subsequent advances in hydrogeologic characterization of arid-zone aquifer systems in the B&R region have their conceptual roots in this early work. Following its establishment in 1879, the USGS was the major institution contributing to regional and local hydrogeologic investigations (Follansbee 1939; Wenzel 1942; Waring and Meinzer 1947; Frazier and Heckler 1972; Maxey 1979; Rabbitt 1989; Davis and Davis 2005; Fryar 2007); but state agency and university programs played an increasingly important role after 1930 (e.g., New Mexico State Engineer Office, Texas Board of Water Engineers, Harvard University, and New Mexico Institute of Mining & Technology). Seminal contributions of Kirk Bryan, N.H. Darton, W.T. Lee, O.E. Meinzer, C.E. Siebenthal, C.S. Slichter, and C.F. Tolman get special attention. ‘‘Hydrogeology in the United States, 1780-1950’’ by Davis and Davis (2005) places some of the material covered in this Note in a much broader regional and temporal context. Because of space limitations, we can mention only a few early contributions of pioneers in well hydraulics and ground water hydrology that this region has produced and/or inspired (e.g., Theis 1935; Hantush and Jacob 1954; Ferris et al. 1962; Reilly 2004; Narasimhan 2006).