Overview of the Groundwater Hydrology of the Rio Grande Basin

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Hydrostratigraphic UnitsMost intermontane-basin fills in the NewMexico region have been subdivided into twomajor lithostratigraphic units (Figure 6), theSanta Fe Group in Rio Grande rift basins (e.g.,Hawley 1978; Chapin and Cather 1994) and theGila Group in basins of the Mexican Highlandand Datil-Mogollon sections to the west (Hawleyet al. 2000). In addition, a clear distinction hasrarely been made between deposits simply classedas “bolson” or “basin” fill and contiguous (formaland informal) subdivisions of the Santa Fe andGila groups. As a first step in organizing availableinformation on basin fill stratigraphy that hasa close relationship with aquifer characteristics, aprovisional hydrostratigraphic classificationsystem (Seaber 1988) has been developed. Itfollows guidelines used successfully in theAlbuquerque and Mesilla basins (Hawley andLozinsky 1992; Hawley et al. 1995) and inadjacent “Southwest Alluvial Basins” as definedby Wilkins (1986, 1998).Hydrostratigraphic units defined in the RGRregion are mappable bodies of basin fill andvalley fill that are grouped on the basis of originand position in both lithostratigraphic and chronostratigraphicsequences. The informal upper,middle, and lower Santa Fe hydrostratigraphicunits (HSUs: USF, MSF, LSF) comprise themajor basin-fill aquifer zones, and they correspondroughly to the (formal and informal) upper,middle, and lower lithostratigraphic subdivisionsof the Santa Fe Groups used in local and regionalgeologic mapping (Figure 6). Dominant lithofaciesassemblages in the upper Santa Fe HSUare LFAs 1-3, 5 and 6. The middle Santa FeHSU is characterized by LFAs 3, 4, 7-9, and thelower Santa Fe commonly comprises LFAs 9, 7-10. Basin-floor facies assemblages 3 and 9 arecommonly present throughout the Santa Fe Groupsection in closed-basin (bolson) areas.The other major hydrostratigraphic unitscomprise channel and floodplain deposits of theRio Grande (RG) and its major tributaries such asthe Rio Chama and Rio Puerco. These valley fillsof Late Quaternary age form the upper part ofthe region’s most productive shallow-aquifersystem (LFAa). Surficial lake and playa deposits,fills of larger arroyo valleys, and piedmont-slopealluvium are primarily in the vadose zone.However, they locally form important groundwaterdischarge and recharge sites. Historicalphreatic conditions exist, or have recently existed,in a few playa remnants of large pluvial lakes ofLate Quaternary age (Hawley 1993). Notableexamples are “gypsum or alkali flats” in theTularosa, Jornada del Muerto and Los Muertosbasins, which are contiguous to, but outside thearea discussed in this paper.Bedrock and Structural Boundary ComponentsStructural and bedrock features that influenceaquifer composition and behavior include basinboundarymountain uplifts, bedrock units beneaththe basin-fill, fault zones and flexures within andat the edges of basins, and igneous-intrusive andextrusive rocks that penetrate or are interbeddedwith basin fill. Tectonic evolution of the faultblockbasins and ranges of the study area (manywith a half-graben structure and accommodationzoneterminations) has had a profound effect onthe distribution of lithofacies assemblages and thetiming and style of emplacement of all majorhydrostratigraphic units (Figs. 5 and 6). Discussionof this topic is beyond the scope of thispaper, however, the reader is referred to pertinentreviews in Collins and Raney (1991), Keller andCather (1994), Hawley and others (1995), Bauerand others (1995), Goff and others (1996), Mackand others (1997, 1998), Faulds and Varga(1998), Haneberg (1998), and Pazzaglia andLucas (1999).HYDROGEOLOGIC FRAMEWORK OFREPRESENTATIVE RGR BASINSFigures 7, 8, and 9 are schematic hydrogeologiccross-sections that illustrate the basicstructural framework and distribution patterns ofmajor hydrostratigraphic units, respectively, in thecentral parts of the San Luis, Albuquerque, andMesilla basins of the Rio Grande rift structuralprovince. In addition to parts of the EspañolaBasin near Los Alamos and the Hueco Bolsonnear El Paso (Purtymun 1995; Cliett and Hawley1996), these are the only areas where high-qualityborehole geophysical and sample logs, and avariety of other geophysical and geochemicalsurvey data are available. It is important to notethat much of this information is related to deep-The Rio GrandeCompact:It’s the Law!Overviewof theHydrogeologyandGeohydrologyof theNorthern RioGrande Basin -Colorado,New Mexico,andTexasWRRIConferenceProceedings199910
The Rio GrandeCompact:It’s the Law!Overviewof theHydrogeologyandGeohydrologyof theNorthern RioGrande Basin -Colorado,New Mexico,andTexasFigure 6. Regional summary and correlation of major lithostratigraphic and basin-fill hydrostratigraphic units(HSUs) in the Rio Grande rift region. Volcanic-rock symbols: Qb-Quaternary basalt; Tb and Tr- Tertiary maficand silicic volcanics, respectively; Tv-primarily intermediate and silicic volcanics.WRRIConferenceProceedings199911
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Overview of the Groundwater Hydrology of the Rio Grande Basin

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