Seismic Investigation Ofthe Buried Horst Between the Jornada Del Muerto and Mesilla Ground-Water Basins Near Lascruces, Dona Ana County, New Mexico

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SEISMIC INVESTIGATION OFTHE BURIED HORST BETWEEN THE JORNADA DEL MUERTO AND MESILLA GROUND-WATER BASINS NEAR LASCRUCES, DONA ANA COUNTY, NEW MEXICO

SANAUGUST1N PASS/ FEET

-5,500

FLUVIAL FACIES

FLOOD-PLAIN DEPOSITS

3,000

U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 97-4147

Prepared in cooperation with the CITY OF LAS CRUCES and the NEW MEXICO STATE ENGINEER OFFICE

Albuquerque, New Mexico 1997 SEISMIC INVESTIGATION OF THE BURIED HORST BETWEEN THE JORNADA DEL MUERTO AND MESILLA GROUND-WATER BASINS NEAR LAS CRUCES, DONA ANA COUNTY, NEW MEXICO

By Dennis G. Woodward and Robert G. Myers

U.S. GEOLOGICAL SURVEY

Water-Resources Investigations Report 97 4147

Prepared in cooperation with the

CITY OF LAS CRUCES and the

NEW MEXICO STATE ENGINEER OFFICE

Albuquerque, New Mexico 1997 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director

The use of firm, trade, and brand names in this report is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey.

For additional information write to: Copies of this report can be purchased from:

District Chief U.S. Geological Survey U.S. Geological Survey Branch of Information Services Water Resources Division Box 25286 4501 Indian School Road NE, Suite 200 Denver, CO 80225-0286 Albuquerque, NM 87110-3929 CONTENTS

Page Abstract...... 1 Introduction ...... ^ 1 Purpose and scope ...... 3 Methodology...... ^^ 3 Well-numbering system...... 5 Hydrogeologic framework of the horst area...... 6 Regional hydrogeology...... 6 Previous understanding of the buried horst...... 8 1988-89 seismic reflection survey...... 25 Data collection and processing...... 25 Data interpretation...... 27 1992 seismic reflection survey ...... 27 Data collection and processing...... 27 Data interpretation...... ^ 33 Results of seismic reflection surveys...... 33 Summary and conclusions...... 36 Selected references...... ~^ 45

PLATE

[Plate is in pocket] 1. Map showing altitude of the water table, as delineated by Wilson and others (1981), and interpreted altitude of the top of the Jornada Horst.

FIGURES

1. Map showing major hydrogeologic features in Dona Ana County, New Mexico...... 2 2. Map showing location of the study area and traces of geologic sections...... 4 3. Diagram showing system of numbering wells in New Mexico...... 5 4. Map showing regional surficial geology...... 7 5. Geologic sections showing: 5A. Buried horst along U.S. Highway 70 (modified from Hawley and others, 1969)...... 10 5B. Buried horst along U.S. Highway 70 (modified from King and others, 1971)...... 11 5C. Buried horst along U.S. Highway 70 (modified from section D-D' in Wilson and others, 1981)...... 12 5D. Buried horst about 4 miles south of U.S. Highway 70 (modified from section E-E' in Wilson and others, 1981)...... 14 5E. Buried horst along U.S. Highway 70 (modified from Gile and others, 1981)...... 16 5F. Buried horst near U.S. Highway 70 (modified from section C-C' in Hawley, 1984)...... 17 5G. Buried horst about 4 miles south of U.S. Highway 70 (modified from section D-D' in Hawley, 1984)...... 18 5H. Horst at Tortugas Mountain (modified from Seager and others, 1987)...... 19 51. Buried horst about 4 miles south of U.S. Highway 70 (modified from section A-A' in Frenzel andKaehler, 1992)...... 20 5J. Buried horst east of Las Cruces (modified from Hawley and Lozinsky, 1992)...... 21 6. Map showing location and water-table altitude of selected wells and test holes...... 22 7. Map showing generalized configuration of the water table, 1976 (from Wilson and others, 1981)...... 23 8. Map showing location of the seismic reflection lines...... 26

Contents iii 9. Geologic sections derived from interpreted seismic profiles located perpendicular to the axis of the Jornada Horst: 9A. Section A-A'...... 28 9B. Section B-B\...... ~ 29 9C. Section C-C'...... 30 10. Geologic sections derived from interpreted seismic profiles located parallel to the axis of the Jornada Horst: 10A. Section D-D\...... ^ 30 10B. Section E-E'...... 31 10C. Section F-F\...... » 32 11. Map showing altitude of the top of the Jornada Horst Tertiary volcanics, as determined from the seismic surveys...... 34 12. Geologic section showing buried horst along U.S. Highway 70, as interpreted from the seismic profiles...... 35

TABLES 1. Summary of geologic-section information for the Jornada Horst area...... 24 2. Well-construction and water-level data for selected wells and test holes near the study area...... 37

CONVERSION FACTORS AND VERTICAL DATUM

Multiply By To obtain

foot 0.3048 meter mile 1.609 kilometer acre 4,047 square meter square mile 2.590 square kilometer pound 453.6 gram

Sea level: In this report, sea level refers to the National Geodetic Vertical Datum of 1929 a geodetic datum derived from a general adjustment of the first-order level nets of the United States and Canada, formerly called Sea Level Datum of 1929.

iv Contents SEISMIC INVESTIGATION OF THE BURIED HORST BETWEEN THE JORNADA DEL MUERTO AND MESILLA GROUND-WATER BASINS NEAR LAS CRUCES, DONA ANA COUNTY, NEW MEXICO By Dennis G. Woodward and Robert G. Myers

Abstract general altitude of the top was discerned by interpretations of the seismic profiles. The Six seismic reflection profiles were presence or absence of large channels incised into collected in the vicinity of the Jornada Horst the top of the horst could not be confirmed by these between Goat Mountain and Tortugas Mountain interpretations. However, the seismic (northeast and east of Las Cruces, New Mexico) to interpretations suggest that the water table is delineate more precisely the geometry of the horst above the top of the horst for most of its extent and to determine whether large, buried channels between U.S. Highway 70 and Tortugas Mountain have been incised into the top of the horst. The and that the top of the horst is above the water Jornada fault zone separates the southern Jornada table and acts as a subsurface flow barrier north of del Muerto ground-water basin from the Mesilla U.S. Highway 70. ground-water basin in the Mesilla drainage basin. The upper part of the Jornada Horst is composed of Tertiary volcanic and volcaniclastic INTRODUCTION rocks; these rocks overlie Permian sedimentary rocks. The horst, in turn, is overlain by Continued growth of the population in the unconsolidated sediments of the upper Santa Fe southern Jornada del Muerto Basin and in the city of Group. Some test holes indicate that little or no Las Cruces requires increased water production from ground water flows from the Jornada del Muerto the Santa Fe Group aquifer (Hernandez and others, ground-water basin to the Mesilla ground-water 1987). Currently (1997), several rural water systems and private domestic wells provide most of the water to basin over some portions of the horst. However, the area. some ground water flows through the upper Santa The southern Jornada del Muerto ground-water Fe Group deposits above some portions of the basin and the Mesilla ground-water basin are located in horst. Ground-water flow immediately east of the the Mesilla drainage basin (fig. 1) in Dona Ana County, horst near U.S. Highway 70 is deflected northward central-southern New Mexico. The Jornada fault zone in the southern Jornada del Muerto ground-water separates the southern Jornada del Muerto Basin from basin presumably because of the change from the Mesilla Basin. A buried horst, bounded on the east higher hydraulic-conductivity values of aquifer by the Jornada fault zone, exists between Goat materials in the southern basin to lower hydraulic- Mountain and Tortugas Mountain northeast of Las conductivity values of materials in the horst. Cruces. Incised, buried channels, if present on the horst, Little is known about subsurface hydrologic could be filled with alluvial material with higher conditions between the Jornada del Muerto Basin and hydraulic-conductivity values than those of the the Mesilla Basin near the horst. The altitude of the top of the horst is considered to be close to the water-table material in the horst. Incised, buried channels altitude in the Jornada del Muerto Basin. Ground water would allow ground water to readily move from immediately east of the horst near U.S. Highway 70 is the Jornada del Muerto ground-water basin to the deflected northward, and some ground water moves Mesilla ground-water basin. from the Jornada del Muerto Basin to the Mesilla Basin The gross geometry of the horst eastern through the upper Santa Fe Group above the horst extent, constraints on the western extent, and (Wilson and others, 1981; Stickel, 1991). Very little POINT OF ROCKS

DON A AN A

MESILLA STUDY DRAINAGE AREA BASIN LasCr BOUNDARY

MESILLA GROUND-WATER BASIN

TEXAS

NEW^EXICO MEXICO

10 20 KILOMETERS

Figure 1 . Major hydrogeologic features in Doha Ana County, New Mexico. ground water moves from the Jornada Basin to the Methodology Mesilla Basin through the lower Santa Fe Group or through the Tertiary volcanic and volcaniclastic rocks Recent advances in seismic reflection geophysics have enabled the investigation of shallow and Permian sedimentary rocks in the horst. If buried subsurface features. Whereas the predominant use of channels are present in the horst, they may transmit seismic reflection geophysics has been for petroleum ground water from the Jornada del Muerto Basin to the exploration at depths of as much as 20,000 feet, the Mesilla Basin. development of new computer applications and high- A better understanding of the relation between frequency seismic sources has promoted the use of the Jornada del Muerto ground-water basin and the seismic reflection geophysics for shallow (commonly Mesilla ground-water basin near the horst could assist at depths from 50 to 2,000 feet) ground-water the New Mexico State Engineer Office and the City of exploration. The propagation of high-frequency seismic signals in the subsurface is attenuated less by Las Cruces in the use and management of the ground- transit through saturated materials than unsaturated water resources in the area. This report was prepared in materials; conversely, high-frequency seismic signals cooperation with the City of Las Cruces and the New are attenuated during transit through unsaturated Mexico State Engineer Office. materials, sometimes to the extent that reflected signals cannot be differentiated from "noise" and subsurface characterization cannot be attempted. Because the Purpose and Scope unsaturated zone above the horst is at least 250 feet thick, the "two-way" travel path of the reflected waves The purpose of this report is to present the through unsaturated material is at least 500 feet long. location and geometry of the buried horst between The seismic signals could be greatly attenuated Goat Mountain and Tortugas Mountain and to discuss transiting this thick unsaturated zone, making it more the hydrogeologic significance of the horst on the local difficult to discriminate the reflected waves from the ground-water-flow system more precisely, to discuss "noise" and to interpret the processed record. whether significant bedrock channels are present on the Contracts for collecting and analyzing seismic reflection data near or within the city of Las Cruces horst surface. If present below the water table, bedrock were awarded "... to determine aquifer thickness, channels could provide preferred pathways for ground- distribution, and geologic structure of the buried ridge water movement from the southern Jornada del Muerto between the Jornada del Muerto and Mesilla ground- ground-water basin to the Mesilla ground-water basin. water basins." The contracts specified that optimum If large, buried channels are not present, the horst geophone spacing shall be used to obtain resolution of could retard or be a partial barrier to the flow of ground buried features in Quaternary and Tertiary sediments at water from the southern Jornada del Muerto ground- depths ranging from 0 to 2,000 feet and with a water basin to the Mesilla ground-water basin. horizontal resolution of 100 feet or less. Because the seismic lines were located near populated areas and This report briefly summarizes previous studies established roads, explosive seismic sources were not conducted near the buried horst and presents the results allowed. For the seismic lines shot parallel to the axis of seismic reflection surveys to determine the location, of the buried ridge (horst), contract requirements size; and shape of the horst and the presence of any further specified that a geophone group spacing no large, buried channels incised into the top of the horst. greater than 50 feet be used. The 50-square mile study area straddles the buried Two different geophysical contractors were used horst between Goat Mountain and Tortugas Mountain to acquire seismic reflection profiles in the study area. (fig. 2). Three seismic reflection lines were located Each contractor used different energy sources, different geophones, and different field spacing (shotpoint offset perpendicular to the horst to locate more accurately the distances and geophone spacing) to collect the data, size, shape, and axis of the horst. Three seismic and each used different data processing techniques to reflection lines were located down the axis of the horst construct, analyze, and interpret the profiles. The U.S. to determine the altitude of the top of the horst and the Geological Survey (USGS) has not attempted to rectify presence or absence of large, buried channels. the seismic profiles as presented by the contractors; 106 45' STUDY AREA BOUNDARY

1 MILE R.2E. EXPLANATION R. 3 E. 1 KILOMETER ^~^~ SECTIONS SHOWN IN FIGURES 5 AND 12 Figure 2.--Location of the study area and traces of geologic sections for example, the structural tops and thicknesses of of land. The four segments denote, respectively, the certain units are not consistent at the intersections of township south of the New Mexico Base Line, the seismic profiles that were prepared by the two range east of the New Mexico Principal Meridian, the contractors. The interpretation of seismic profiles is section, and the particular 10-acre tract within the subjective and results in a non-unique solution. The section. discussion of the contractors' interpreted profiles in The fourth segment of the number consists of this report does not imply endorsement or acceptance three digits denoting, respectively, the quarter section by the USGS of the interpretations and conclusions of or approximate 160-acre tract, the quadrant the contractors. The seismic profiles are in the files of (approximately 40 acres in size) of the quarter section, the USGS District Office in Albuquerque and the New and the quadrant (approximately 10 acres in size) of the Mexico State Engineer Office in Santa Fe. 40-acre tract in which the well is located. The system of numbering quarter sections and quadrants, which is Well-Numbering System done in reading order, as well as the usual numbering of sections within a township, is shown below (fig. 3). Wells are located according to the system of For example, well 23S.01E.24.344 is located in the SE common subdivision of sectionized land used 1/4 of the SE 1/4 of the SW 1/4 of section 24, Township throughout the State by the USGS. The number of each 23 South, Range 1 East. If more than one well has the well consists of four segments separated by periods and same location number, the letter "a" is assigned to the locates the position of a well to the nearest 10-acre tract second well, the letter "b" to the third well, and so on.

WeM23S.01E.24.344

Figure 3.-System of numbering wells in New Mexico. HYDROGEOLOGIC FRAMEWORK OF THE The Quaternary and Tertiary Santa Fe Group HORST AREA overlies Tertiary volcanic and associated sedimentary rocks of early Oligocene to Miocene age and underlies The geology and hydrogeology of the area Quaternary alluvial deposits that postdate the between Las Cruces and the Organ Mountains to the beginning of the Rio Grande Valley entrenchment in east have been described in a variety of studies. This the middle Pleistocene (Hawley and others, 1969, somewhat desolate area has a rather unassuming p. 52). The thickness and width of the Santa Fe Group surface appearance, but hidden beneath that surface an decrease from the north toward the south in the important buried geologic feature physically separates southern Jornada del Muerto Basin (Hawley, 1984; two regional ground-water basins: the Jornada del Peterson and others, 1984). Well data and geophysical Muerto Basin on the east and the Mesilla Basin on the tests (Doty, 1963; Hawley and Kottlowski, 1965; west. That important geologic feature, the Jornada Taylor, 1967) indicate that the Santa Fe Group is more Horst, is an uplifted, north-trending block of bedrock. than 1,000 feet thick in the central part of the southern The altitude of the buried top of this horst is considered Jornada del Muerto Basin. to be close to the altitude of the water table in the Fluvial deposits in the Santa Fe Group generally Jornada del Muerto basin, and the horst could act as a are more permeable than alluvial-fan deposits (Wilson partial barrier to regional ground-water flow. and others, 1981). The thickness of fluvial deposits There is speculation, however, that paleostreams decreases from the western edge of the southern could have eroded channels into the top of the horst and Jornada del Muerto Basin toward the eastern edge of filled those fluvial channels with coarse-grained the basin where they are absent. Fluvial deposits in the alluvium. Finer grained, alluvial-fan sediments were Jornada del Muerto Basin in the northern part of the deposited throughout the area over the horst and would basin are not present in the southern end of the basin have buried the speculative bedrock channels. If those (Hawley, 1984; Peterson and others, 1984; Mack, buried channels exist and are below the water table in 1985). Seager and others (1987) mapped the Santa Fe the Jornada del Muerto Basin, they could function as Group exposed in the vicinity of the horst as consisting preferred pathways for ground-water flow between the of alluvial-fan and fluvial deposits composed of clay, Jornada del Muerto Basin and the Mesilla Basin and silt, sand, gravel, and caliche of the Camp Rice could provide substantial subsurface recharge to or Formation, which correlates with the upper Santa Fe discharge from the Mesilla ground-water basin. Group. The regional surficial geology of the study area is mapped in figure 4. Regional Hydrogeology The upper Santa Fe Group (middle Pliocene to middle Pleistocene) in the Mesilla Basin, correlative In New Mexico, the Mesilla Basin constitutes with the Camp Rice Formation, has been recognized the southernmost basin in a north-south-trending series and mapped throughout the Mesilla and Jornada del of structural basins that compose the Rio Grande Rift. Muerto Basins. The dominant facies of the Camp Rice The rift extends from the San Luis Basin in southern Formation consists of fluvial sand and pebbly sand Colorado through New Mexico to the Hueco Bolson deposited by the ancestral Rio Grande; a secondary and Bolson de los Muertos in western Texas and facies consists of piedmont-slope deposits composed northern Chihuahua, Mexico (Hawley, 1978). The primarily of fan alluvium (Hawley and Lozinsky, southern Jornada del Muerto Basin is bounded on the 1992). As shown in figures 5A and 5E, the sediments north by a structural change from a graben to a syncline near the horst consist of upper Santa Fe Group deposits near the Point of Rocks at the Dona Ana-Sierra County consisting of an upper alluvial-fan facies, a fluvial line; on the east by the San Andres, San Agustin, and facies, and a lower alluvial-fan facies. The thickness of Organ Mountains; and on the south and west by the the Camp Rice Formation ranges from about 300 to Jornada fault zone (fig. 1). The Santa Fe Group 700 feet in the central basin areas (Hawley and includes all basin fill that was deposited prior to the Lozinsky, 1992, p. 27), yet Wilson and others (1981, formation of the Rio Grande Valley in the early to p. 38) reported a thickness of more than 1,300 feet in middle Pleistocene. The major aquifer system in the rift test hole 23S.01E.13.411 located just west of the horst basins is composed of the saturated sediments in the near Las Cruces. Wilson and others (1981, p. 40) upper Santa Fe Group. thought that the saturated thickness of the alluvium on Qcf 106*50'

STUDY AREA BOUNDARY

Qvy

40'

Qcp Geology from Seager and others, 19B7 EXPLANATION ARROYO-CHANNEL. TERRACE, AND FAN DEPOSITS CAMP RICE FORMATION FLUVIAL FACIES RIO GRANDE FLOOD-PLAIN AND CHANNEL DEPOSITS CAMP RICE FORMATION TRANSITIONAL FACIES OLDER RIVER, ARROYO, AND ALLUVIAL-FAN DEPOSITS CAMP RICE FORMATION, PIEDMONT-SLOPE OLDER PIEDMONT-SLOPE DEPOSITS and FANGLOMERATE FACIES, UNDIVIDED FLOW-BANDED RHYOLITE YOUNGER PIEDMONT-SLOPE DEPOSITS CONTACT AFTON BASALT CAMP RICE FORMATION SEDIMENTS ASSOCIATED WITH FAULT-Ball on downthrown side; dashed where LA MESA SURFACE Inferred at the surface; dotted where burled CAMP RICE FORMATION, PIEDMONT-SLOPE FACIES SELECTED OIL OR WATER HOLE UNDIFFERENTIATED Qvy and Qvo CAMP RICE FORMATION--Approximate known CAMP RICE FORMATION PIEDMONT-SLOPE FACIES limits of fluvial deposits Figure 4. Regional surficial geology. top of the horst may be very thin, but also thought it barrier formed a ground-water dam; note the data point probable that the upper surface of the horst had peaks located in the bedrock high that suggests apparent and troughs. Surface electrical resistivity soundings ground-water flow through the bedrock (fig. 5A). King were made by Wilson and others (1981) to estimate the and others (1971) declared the southern Jornada del thickness of the Santa Fe Group near the horst (figs. 5C Muerto Basin to be a well-defined structural basin and 5D). The known total thickness of the upper Santa separated from the Mesilla Basin by a buried bedrock Fe Group is at least 250 feet on the horst (Mack, 1985, high extending from the Dona Ana Mountains to p. 61); the maximum thickness is unknown. Tortugas Mountain. A geologic section presented in Tertiary volcanic and volcaniclastic rocks their report (King and others, 1971, fig. 5, p. 19) underlie the Santa Fe Group (figs. 5A, 5B, and 5E) and overlie Permian sedimentary rocks on the horst (figs. showed the general position of this bedrock high and its 5F, 5G, and 5J). The approximate location of the horst marked effect on the water-table configuration is known from gravity surveys, surface electrical (fig. 5B). Furthermore, on the basis of the presence of resistivity surveys, and a few test holes and wells. gravels derived from the Organ Mountains (situated Tertiary rocks include rhyolitic to andesitic lava flows, east of the bedrock high) found in wells west of the ash-flow tuffs, laharic breccias, conglomerates, bedrock high, King and others (1971, p. 20) surmised sandstones, and mudstones (King and others, 1971; that (1) the buried uplift is locally breached in the area Hawley, 1984; Mack, 1985). Almost no work has been east of Interstate 25, between U.S. Highway 70 and done to identify the stratigraphy of the Tertiary Tortugas Mountain and (2) the uplift is not a volcanic and volcaniclastic rocks on the horst, but W.R. continuous barrier to ground-water movement in the Seager (Mack, 1985) identified cuttings of the Palm Santa Fe Group basin fill. Park Formation from one City of Las Cruces test hole (22S.02E. 10.444). Wilson and others (1981) constructed The aquifer in the upper Santa Fe Group in the geohydrologic sections of the area based on new well southern Jornada del Muerto Basin is recharged by data and surface electrical resistivity surveys; those mountain-front runoff from precipitation and sections indicate that (1) the bedrock high is bounded snowmelt from the San Andres, San Agustin, Organ, on the east and west by faults; (2) the altitude of the and Dona Ana Mountains and by percolation of runoff water table, 1967-75, approximated the altitude of the in arroyos and playa lakes. Some runoff occasionally bedrock high along a section that crossed the horst reaches the Mesilla Basin and the Rio Grande. Some along the same transect as U.S. Highway 70 (fig. 5C); ground water flows across the horst from the Jornada and (3) the altitude of the water table, 1967-76, was del Muerto Basin to the Mesilla Basin; the volume of about 165 feet above the top of the buried bedrock high this flow through the horst is unknown at this time. along a section that crossed the horst about 4 miles Buried, incised channels, filled with coarser alluvium south of U.S. Highway 70 (fig. 5D). (with higher hydraulic conductivities), would potentially allow more ground water to flow from the In 1979, the City of Las Cruces drilled three test Jornada del Muerto Basin to the Mesilla Basin. holes (23S.02E.15.322, 22S.02E.34.244, and 22S.02E. 10.444) in the area that provided further information about the depth to the top of the Tertiary Previous Understanding of the Buried volcanic and volcaniclastic rocks on the horst or Horst bedrock high (Mack, 1985). Test hole 23S.02E. 15.322 was 785 feet deep and did not penetrate bedrock; test The presence of a buried bedrock high east of hole 22S.02E.34.244 penetrated bedrock at a depth of Las Cruces composed of Tertiary volcanic and 250 feet; and test hole 22S.02E. 10.444 penetrated volcaniclastic rocks has been known for at least 25 years. The horst, composed of Tertiary volcanic and bedrock at a depth of 650 feet. The geologic section volcaniclastic rocks, exists roughly between Goat published by Gile and others (1981) was the first to Mountain and Tortuga Mountain northeast of Las show the Camp Rice Formation (upper Santa Fe Cruces. This Tertiary volcanic high was shown in a Group) above and adjacent to the upper portion of the geologic section by Hawley and others (1969, fig. 3, horst (fig. 5E). The most detailed geologic sections p. 57). That section suggested that the buried bedrock across the Jornada Horst were presented by Hawley (1984); he mapped lithofacies in the Santa Fe Group The Jornada Horst affects regional ground-water that showed only upper Santa Fe Group deposits flow, as indicated by the water-level map (fig. 7) from directly above and surrounding the upper portion of the Wilson and others (1981); the location of the eastern Jornada Horst (figs. 5F and 5G). Hawley's sections extent of the horst, as delineated from the seismic agree with those of Wilson and others (1981) in that the sections collected for this report, coincides with a water-table altitude is shown to be (1) close to the top deflection of ground-water flow to the north near U.S. of the horst in the section close to U.S. Highway 70 Highway 70. This deflection is caused by the change (figs. 5C and 5F) and (2) more than 100 feet above the horst in a section about 4 miles south of U.S. Highway from higher hydraulic-conductivity values in the upper 70 (figs. 5D and 5G). Seager and others (1987) Santa Fe Group to the lower hydraulic-conductivity presented an east-to-west geologic section through values of the Tertiary volcanics and volcaniclastics and Tortugas Mountain that indicated multiple faults Permian sedimentary rocks of the horst between Goat bounding the uplifted bedrock (fig. 5H). The Mountain and Tortugas Mountain, thus forcing much geohydrologic section presented by Frenzel and of the ground water to flow north. The wells clustered Kaehler (1992) shows the approximate water table north of U.S. Highway 70 and east of the Jornada fault above the top of the bedrock high and suggests ground- zone have rather similar water-level altitudes that range water flow partly through the bedrock (fig. 51). from 4,065 to 4,087 feet above sea level (fig. 6). The Hawley and Lozinsky (1992) showed the bedrock high, low water-level gradient in this area contrasts with the bounded by numerous faults, in a geologic section (fig. 5J) and called the feature the Dona Ana-Tortugas steeper gradients elsewhere in the study area and Uplift (buried). suggests that the horst north of the highway could be a One of the conclusions of a ground-water more effective barrier to ground-water flow. The water- modeling report of the Mesilla Basin by Peterson and table map by King and others (1971) shows a similar others (1984, p. 135) was that "A northwest-southeast- ground-water-flow deflection to the north in the same trending fault block of volcanic and sedimentary general area. Stickel (1991) determined that the horst bedrock has been elevated in an area just to the east of alters the direction of ground-water flow in the Las Cruces, creating a submerged horst that acts as a southern Jornada del Muerto Basin and mentioned that partial barrier to ground-water flow coming from the basin fill on top of the horst transmits some ground piedmont slope in the northeast section of the basin. water from the Jornada del Muerto Basin to the Mesilla Ground water passes westward over the structure in Basin in some areas. Table 1 summarizes the geologic- areas where the top of the bedrock is lower than the section information from a variety of studies conducted others. The 'damming' effect of the horst partly contributes to the steep piezometric head gradient in the area. observed in the alluvial facies below the Organ In summary, the horst is overlain by upper Santa Mountains." Fe Group sediments (the Camp Rice Formation); the Other previous studies (King and others, 1971; thinnest cover of sediments on the horst was Wilson and others, 1981) indicate that most ground encountered in City of Las Cruces test hole water south of U.S. Highway 70 flows west from the 22S.02E.34.244, which penetrated bedrock at a depth Organ Mountains into the Mesilla ground-water basin. of 250 feet. Near U.S. Highway 70, the altitude of the The direction of ground-water flow was based on top of the horst is close to the water-table altitude, and potentiometric contours constructed from depth-to- the top of the horst is higher (figs. 5A, 5B, and 5E). water information for wells completed in the Santa Fe Wilson and others (1981) showed that the top of the Group aquifer. However, well control is sparse in the horst about 4 miles south of U.S. Highway 70 is at an area of the horst, and consequently very little data are approximate altitude of 3,750 feet and that the water available for that area (fig. 6). Ground-water-level data for the area are primarily from wells near U.S. table (using data from 1967-76) is at least 165 feet Highway 70, from wells on the upthrown block east of above the top of the horst (fig. 5D); thus, the horst in the major step fault parallel to the Organ Mountains, this area would not prevent westward ground-water and from wells on the west side of the horst between flow from the southern Jornada del Muerto Basin to the Goat Mountain and Tortugas Mountain. Mesilla Basin. Ground-water surface profile. = Rio Grande alluvium Dots show where measured

_ k. c'» Late Quaternary valley-slope deposits, J5.Q mainly Fillmore and Picacho alluviums

.£ c Late Quaternary basin fill-Mainiy Organ and pre-Organ/post-Jornada surface fans

Upper alluvial-fan facies, including thin, sandy to clayey basin-floor deposits

= Fluvial f acies-l = zone where an Irvingtonian Q vertebrate fauna has been recovered u.

Lower alluvial-fan facies-Probably includes Southern lake and playa beds below 3,800 feet Jornodo d«l Muerfo ~ Tertiary volcanics p6 Precambrian, Paleozoic, and early to mid-Cenozoic rocks WEST 4,500' 4,500' .. f.*.*.*«.* * »~ SS^vW. *::::::

4,000' 4,000'

3,500' 3,500'

Datum is sea level SMILES APPROXI MATE EXTENT OF STU DY AREA -H I 1 2 5 KILOMETERS Figure 5A.--Buried horst along U.S. Highway 70 (modified from Hawley and others, 1969). Trace of section shown in figure 2. CQ"T] c CD 01 CO

cn- *

CD O Q. CD ^ °

O O 3

O CO m T 3 I x

Ifc » =;<< m CD ^4 31 ruo |-CD m O Q. CD"^» Q. o 3

Q. fO i-

m > OT WEST EAST

5,500' ' - 5.500'

_ =* W^ > (B/lN = = 5,000' - - -^0... K)10

CM r*~~ CJ x^2B- 4,500' - x <> c~> O X v> < r~~^?w X> ^ C - ^ii Sand a ,d gravel » OTt 23 _,_ Wottr la tit ~^I967-7S 4,000' - ISO 33 78 w- Sand and clay ^_ 3,500' - 69

r Sand and gravel 32

3,000' - Sand, silt and clay Sand and clay

- 2,500' 2,500 \

2,000' - Sand>clay - 2,000' Igneous / rock 7

1,500' - . 1,500' \ HORST pQTs

1,000'- CHANGE IN SCALE \ CHANGE IN SCALE - 1 ' 000 ' Sea \ Sea level ^** level 5,000 -1,000' -1,000'

-APPROXIMATE EXTENT OF STUDY AREA'

01234 SMILES i i i i___i____| 01234 5 KILOMETERS

VERTICAL EXAGGERATION ABOVE ALTITUDE OF 1,000' X 11 VERTICAL EXAGGERATION BELOW ALTITUDE OF 1,000' X 3 Figure 5C.--Buried horst along U.S. Highway 70 (modified from section D-D' in Wilson and others, 1981). Trace of section shown in figure 2. EXPLANATION GEOLOGIC DATA

Qal Holocene alluvium (Quaternary) Mainly flood-plain deposits of the Rio G rande and tributaries. Contains clay, silt, sand, and gravel QTs Santa Fe Group-Pleistocene Mainly valley-fill deposits composed of clay, to middle Miocene (Quaternary silt, sand, gravel, conglomerate, and volcanic and Tertiary) rocks pQTs Pre-SantaFe Group-Middle Consists of sedimentary, metamorphic, and igneous Miocene (Tertiary) to rocks. Includesundifferentiated volcanic and Precambrian rocks intrusive rocks Probable dominant lithology of units is labeled in selected areas. Sand> clay denotes sand content greater than clay content Contact Approximately located or inferred contact Fault or Zf Approximately located Arrows indicate direction of fault zone ' or inferred fault relative movement xxxxx Depth in well or test hole where hard, indurated rock (bedrock) was penetrated WELL DATA VERTICAL ELECTRICAL SOUNDING DATA BEND IN SECTION TOTAL DEPTH OF WELL, IN FEET CO LU ELECTRICAL SOUNDING

WELL LOCATION NUMBER-Parentheses around CM the well number indicate the well is projected CO to the section line at a right angle 6 CO iii LOCATION NUMBER

CO CM o Domestic CM Irrigation -O VERTICAL ELECTRICAL SOUNDING © Public-water supply 170 V^-oTest hole RESISTIVITY-Number is the true resistivity, in ohm-meters, of 140 interval. Intervals separted by . Electrical basement is indicated by 150

NOTE: Vertical line through well symbol indicates unused or abandoned well

Figure 5C.--Buried horst along U.S. Highway 70 (modified from section D-D' in Wilson and others, 1981). Trace of section shown in figure 2--Concluded. WEST EAST

ion 5,500' ton Volcanic , ,nn> mv> rock \xT 5'500

5,000' - 5,000'

4,500' - - 4,500'

4,000' - - 4,000'

3,500' - - 3500'

3,000' - - 3,000'

2,500' - - 2,500'

2,000' - 2,000'

1,500'

CHANGE IN SCALE - 1,000' Sea level APPROXIMATE EXTENT OF STUDY AREA

01234 5 KILOMETERS VERTICAL EXAGGERATION ABOVE ALTITUDE OF 1,000' X 11 VERTICAL EXAGGERATION BELOW ALTITUDE OF 1,000' X 3

Figure 5D.-Buried horst about 4 miles south of U.S. Highway 70 (modified from section E-E' in Wilson and others, 1981). Trace of section shown in figure 2. EXPLANATION GEOLOGIC DATA

Qal Holocene alluvium (Quaternary) Mainly flood-plain deposits of the Rio Grande and tributaries. Contains clay, silt, sand, and gravel QTs Santa Fe Group-Pleistocene Mainly valley-fill deposits composed of clay, to middle Miocene (Quaternary silt, sand, gravel, conglomerate, and volcanic and Tertiary) rocks pQTs Pre-Santa Fe Group-Middle Consists of sedimentary, metamorphic, and igneous Miocene (Tertiary) to rocks. Includes undifferentiated volcanic and Precambrian rocks intrusive rocks Probable dominant lithology of units is labeled in selected areas. Sand > clay denotes sand content greater than clay content Contact Approximately located or inferred contact Fault or */ Approximately located Arrows indicate direction of fault zone ,* or inferred fault relative movement xxxxx Depth in well or test hole where hard, indurated rock (bedrock) was penetrated WELL DATA VERTICAL ELECTRICAL SOUNDING DATA

TOTAL DEPTH OF WELL, IN FEET Bend in section WELL LOCATION NUMBER-Parentheses around CO the well number indicate the well is projected LJJ ELECTRICAL SOUNDING to the section line at a right angle CM d CO - -Stock LOCATION NUMBER CO 0 Domestic CO - Irrigation VERTICAL ELECTRICAL SOUNDING "^Industrial © Public-water supply 150 RESISTIVITY-Number is the true resistivity, in ohm-meters, of -o-Test hole interval. Intervals separted 42 by i Electrical basement is indicated by

26 NOTE: Vertical line through well symbol indicates unused or abandoned well

Figure 5D.--Buried horst about 4 miles south of U.S. Highway 70 (modified from section E-E' in Wilson and others, 1981). Trace of section shown in figure 2-Concluded. ::::: _ RioGrandealluvium Ground-water surface profile. :::: '.: . : : Dots show where measured ll = 2 Late Quaternary valley border deposits, ss N.N> ">, «- mainly Picachoand Fillmore alluviums East S& San § Late Quaternary basin fill and Jomada, §, Isoacks Ranch, and Organ alluviums Sstln

g Upper alluvial-fan facies, including thin, '"I"I" " " ' i-j °- = sandV to clayey basin-floor deposits il o E o Fluvial facies I = zone where an Irvingtonian vertebrate fauna has been recovered

:vf{:-ft:{:J^ ^ Lower alluvial-fan facies Probably includes lake and playa beds below 3,900 feet Southern T Tertiary volcanlcs Jornadadel pC Middle to lower Cenozoic, Paleozoic, and Muerto Precambrian rocks West 4,500' 4,500'i

4.000' - 4,000'

3,500' 3.500'

Datum is sea level APPROXIMATE EXTENT OF STUDY ARE A 01234 5 MILES

01234 5 KILOMETERS

Figure 5E.--Buried horst along U.S. Highway 70 (modified from Gile and others, 1981), Trace of section shown in figure 2.

16 West East Jornodo fault toni

Mesiiia Vaiiey fault zone

5.000' 5,OOO'

4,000' 40OO

3,000' J

2,000' - zpoo

SMILES

01234 5 KILOMETERS

EXPLANATION

Tri Rhyolitic intrusive complexes Mostly sills, 2 plugs, and associated lava domes HIGH-ANGLE NORMAL FAULTS- E §O Ti Silicic to intermediate plutonic rocks Dashed where inferred; direction of iu -. relative displacement TV Andesitic and other intermediate volcanic and 3,900' volcaniclastic rocks Includes lavas and WELL-On or near line of section; laharic breccias land-surface altitude and total depth Upper Paleozoic rocks Includes limestone, shale, 777T ELECTRICAL BASEMENT N and minor sandstone O 111 PI Lower Paleozoic rocks-Undivided; includes limestone, shale, and minor sandstone

Figure 5F.--Buried horst near U.S. Highway 70 (modified from section C-C' in Hawley, 1984). Trace of section shown in figure 2.

17 West East

6,000'

5,000' 5,000' Mesilla - Valley T fault zone a » ?l f (3 - s2 ? £.9 «~ 35 * 4,000' 3,891 3,892 3

3*0 *>'<: 3,000''

-r ' 2,000'. -T 4 t--s ! <- 1 / J > 1 ' J <> / V / i~" / hs-~>^r-_ - 1 Tfy

111 111 UjQUJ oz" _ EXPLANATION O

5,000' ~ Tortugas Jornada Jornadadel Muerto - 5,000' Mountain fault zone Basin

SEA LEVEL -SEA LEVEL

-5,000' - - -5,000' Tis

-10,000' - - -10,000'

SMILES j 5 KILOMETERS

GC LU EXPLANATION O O N Pu UPPER PALEOZOIC ROCKS-lncludes TQa TERTIARY AND QUATERNARY O BASIN FILL AND ALLUVIUM HI limestone, shale, and minor sandstone Tis SILICIC PLUTONIC ROCKS PI LOWER PALEOZOIC ROCKS-Undivided; includes limestone, shale, and minor sandstone VOLCANIC ROCKS OF ORGAN CAULDRON UJGC pG PRECAMBRIAN ROCKS-Metasedimentary rocks, LLJ > 8 Twl West-side lavas GCCO metavolcanics, and granite GC O Ts Tuff of Squaw Mountain < IJ O F o Ta Tuff of Achenback Park GC FAULT-Dashed where inferred; direction UJ BELL TOP FORMATION of relative displacement To Orejon Andesite

TV Volcanic rocks

Figure 5H.--Horst at Tortugas Mountain (modified from Seager and others, 1987) Trace of section shown in figure 2. WEST EAST

FEET 7,000 -

Mesilla Basin as defined for this study 6,000 -

EAST ROBLEDO 5,000 - FAULT Land surface ZONE Main part of Las Cruces Flood-plain alluvium well field 4,000 -

3,000 -

2,000- -2,000

1,000 - -1,000

Sea Sea level level 5 MILES \ i i i i i 01234 5 KILOMETERS VERTICAL EXAGGERATION X 10

EXPLANATION Fault Dashed where inferred. Arrows indicate direction of relative vertical movement Approximate contact between Santa Fe Group and underlying bedrock Possible path of underflow into the basln--X indicates flow in the Santa Fe Group; Y indicates flow partly through bedrock; Z indicates very deep flow Possible path of flow from flood-plain alluvium

Figure 51.-Buried horst about 4 miles south of U.S. Highway 70 (from section A-A' in Frenzel and Kaehler, 1992). Trace of section shown in figure 2.

20 vz

CD (f)

(Q C CD 01

00 C H C 3 ®"

o Q. EAST ROBLEDO CD IT FAULTZONE

^CO .-i- Boles & Assoc. No. 1 Fed. m o md CO r- > CD o£P o> 2 w Z! m I ° X RIO GRANDE = o MESILLA VALLEY c'l FAULTZONE

5 3 ro o Q.

CD" 33 O 3 | m ^ " S Q. O m w DONA ANA > 33 TORTUGAS o 3° UPLIFT (buried) 3 o o I oN oN v o o §. CD *< V s >< 3 Q.

O N

CO CO ORGAN MOUNTAINS m

® 106 45' 106 37'30"

32 25'

STUDY AREA BOUNDARY

32 17' 30"

R.1 E. R.2E. R.3 E. Base map from USGS digital data, EXPLANATION scales 1:1OO,OOOand 1:5OO,OOO HIGHEST AREA OF THE HORST MILES

3 KILOMETERS FAULT-Location from seismic interpretation; U, upthrown side; X D, downthrown side WELL OR TEST HOLE- 3,830 Number is altitude, in feet above sea level, of water table from most recent measurement (1961-94; table 2; Wilson and others, 1981) Figure 6.--Location and water-table altitude of selected wells and test holes. 22 106 45' 106 37' 30"

32 STUDY 25' AREA BOUNDARY

3217' 30"

R.1 E. R.2 E. R.3 E. Base map from USGS digital data, scales 1:1OO,OOO and 1:5OO.OOO n i i -|23 KILOMETERS EXPLANATION

v WATER-LEVEL CONTOUR-- FAULT-Location from x Intervals 20 and 100 feet. seismic interpretation. Datum is sea level U, upthrown side; D, downthrown side

Figure 7.-Generalized configuration of the water table, 1976 (from Wilson and others, 1981). 23 Table 1 . Summary of geologic-section information for the Jornada Horst area

[--, no data; Tis, Tertiary intermediate silicic plutonic rocks; QTs, Quaternary and Tertiary sand]

Approximate Horst or bedrock altitude of top of Referenced geologic high bound by Description of horst above sea Relation of water table to Description of material section faults? horst material level horst directly above horst Figure 5A. Section from No Tertiary volcanics 4,060 feet Coincident with top of Lower alluvial-fan facies Hawley and others (1969) horst on east and within in Santa Fe Group horst on west. Figure 5B. Section from No Volcanic rock 4,000 feet Coincident with top of Alluvial-fan facies King and others (1971) horst on east and within horst on west. Figure 5C. Section from Yes Igneous rock 3,960 feet Coincident with top of Sand and gravel Wilson and others (1981) horst. Figure 5D. Section from Yes Volcanic rock 3,750 feet Water table (1967-76) Sand and clay Wilson and others (1981) about 165 feet above top of horst. Figure 5F. Section from Yes Tertiary volcanics 4,000 feet Water table above horst Upper Santa Fe Group Hawley (1984) on east and below on west. Figure 5G. Section from Yes Tertiary volcanics 3,700 feet Water table about 120 Upper Santa Fe Group Hawley (1984) feet above top of horst. Figure 5H. Section from Yes Tis ~ Top of horst above land ~ Seager and others (1987) surface. Figure 51. Section from Yes Bedrock 3,750 feet Water table 160 feet Santa Fe Group Frenzel and Kaehler (1992) above top of horst. Figure 5J. Section from Yes Tertiary volcanics QTs Hawley and Lozinsky (1992) Figure 12. Seismic sections Yes Volcanic rock 4,070 feet ~ Upper Santa Fe Group from this report 1988-89 SEISMIC REFLECTION SURVEY Microcomputer software specifically designed for this system was used to process the seismic data. Charles B. Reynolds and Associates of Processing steps included transcription from the field Albuquerque, New Mexico, recorded four seismic digital recordings to the computer; reformatting of data reflection profiles under contract for the USGS during to the computer format; verification of data quality and 1988 and 1989; the location of the seismic reflection editing; determination of the thickness and velocity of lines are shown in figure 8. Three of the profiles (A-A', the surface, low-velocity (weathering) layer and the B-B', and C-C') were established perpendicular to the velocity of the subweathering layer by analyzing the axis of the horst and south of U.S. Highway 70 to refraction returns; application of an F-K filter or locate the highest areas along the axis of the horst. One velocity filter to remove unwanted "noise" on the profile (D-D') was established parallel to the axis of the recordings; time-variant deconvolution using three horst north of U.S. Highway 70 to locate any large, operators; 600-percent common depth point stacking; incised, buried arroyo channels (Reynolds, 1989). application of datum (static and dynamic) corrections; application of a coherence filter that enhances seismic events dipping less than 20 degrees in either direction; Data Collection and Processing frequency filtering; trace normalization; and variable area-wiggle trace plotting (Reynolds, 1989). Field instrumentation included a multichannel The lengths and mean velocities for profiles E.G. & G. Geometries Nimbus ES121 OF seismograph, A-A', B-B', C-C', and D-D' are: equipped with frequency filters, and a G724S digital recorder. The geophone array consisted of six Mark Products G-21 10-hertz, gimbal-mounted, self- Mean velocity orienting drag geophones attached to cables towed Length of of surface Mean velocity of Seismic Number of profile (weathering) layer subweathering layer behind the seismic truck. The seismic energy source profile shot points (miles) (feet per second) (feet per second) was a patented, bounceless weight of 550 pounds A-A' dropped 6.5 feet to the ground. The output of each 898 5.61 1,800 3,300 B-B' 480 3.00 2,300 3,600 receiver was recorded separately. C-C' 160 1.00 1,800 3,000 The seismic reflection surveys were designed to D-D' 280 1.75 1,700 2,600 investigate the subsurface to a depth less than 2,000 feet below land surface (Reynolds, 1989). Field and In seismic geophysics, the term "weathering recording parameters included the following: layer" refers to materials at the land surface that have a (1) The geophones were located at distances of considerably slower velocity than slightly deeper rocks 66, 131, 197,262, 328, and 394 feet behind (Coffeen, 1986). The weathering velocities used in the the shot (impact) point, and the output of correction calculations were those measured on each each geophone was recorded separately. profile, and the replacement (subweathering) velocity (2) One to three weight drops were made at used was 3,300 feet per second except on profile D-D', each shot point, which were located 33 feet where a velocity of 2,600 feet per second was used. apart along the line being recorded. The mean velocities of both layers decreased toward (3) There were 160 shot points (and subsequent the west on line A-A'. recordings) per mile, resulting in a 600- percent common depth point stacking. (4) 60-hertz notch filters were used where power lines were close to the seismic line. (5) The digital record length was 1 second, with a sampling interval of 1 millisecond. (6) The processing datum selected was land surface. (7) The lines were surveyed and tied to unmarked survey monuments using estimated altitudes from 1:24,000-scale topographic maps for vertical control.

25 106 45

STUDY AREA BOUNDARY

R.2E. R.3E.

1 MILE EXPLANATION

1 KILOMETER "K SHOT POINT AND STATION NUMBER

0 CONTROL WELL--Well subsurface Exxon Beard Ole Fed. No. 1 information used

Figure 8.--Location of the seismic reflection lines.

26 Data Interpretation unconsolidated Tertiary (near top of the Tertiary volcanics) as determined from five wells. Three geologic boundaries were delineated and A mean velocity of 9,400 feet per second for a traced on the seismic profiles: the base of the upper refractor at a depth of 110 feet below land surface was Santa Fe Group, base of the lower Santa Fe Group (top detected at the east end of line B-B' (from stations 315 of the Tertiary volcanics), and base of the Tertiary to 480). Reynolds (1989) interpreted this as a volcanics. The well control (fig. 8) used by Reynolds consolidated sandstone, conglomerate, or basalt flow (1989) to correlate seismic horizons with geologic within the upper part of the Santa Fe Group. boundaries was:

Depth, 1992 SEISMIC REFLECTION SURVEY Well Geologic boundary in feet Digitec Seismic Corporation of Aurora, 22S.02E.28.3334 Top of Tertiary volcanics 503 Colorado, collected two seismic reflection profiles Apodaca Park Base of upper Santa Fe Group 452 under contract for the USGS during October 1992. (23S.02E.07.122) Top of Tertiary volcanics 710 Profiles E-E' and F-F' were located parallel to the axis City of Las Cruces No. 39 Base of upper Santa Fe Group 125 of the horst south of U.S. Highway 70 (fig. 8) to locate (23S.02E.06.240) Top of Tertiary volcanics 398 any large, incised, buried arroyo channels (Moriarty, Exxon Beard Ole Fed. No. 1 Base of upper Santa Fe Group 167 1992). Both profiles run about northwest to southeast (23S.02E.il. 134) Top of Tertiary volcanics 476 and are separated by about a half mile. Profile E-E' Base of Tertiary volcanics 790 extends from U.S. Highway 70 toward the City of Las 22S.02E.2 1.444 Top of Tertiary volcanics 365 Cruces landfill for about 3.1 miles and crosses profile A-A' in Alameda Arroyo. Profile F-F' begins near the The reflection horizon that correlated with the City of Las Cruces landfill near the west end of profile base of the upper Santa Fe Group, as reported above by B-B' and extends approximately southeast for about 1 Reynolds (1989), was determined by the interpretation mile. Profile F-F' crosses profile C-C'. of gamma-ray borehole-geophysical logs collected from the three wells listed above. These log picks could possibly represent the base of a facies change within Data Collection and Processing the Camp Rice Formation (upper Santa Fe Group) rather than the base of the upper Santa Fe Group (John The field instrumentation included a 48-channel Hawley, New Mexico Bureau of Mines and Mineral Bison Instruments 9048 signal-enhancement Resources, oral commun., 1997). Recent well logs (not seismograph. The geophone array consisted of six available at the time of the seismic surveys) show Mark Products L-25 30-hertz geophones equally upper Santa Fe Group deposits directly overlying the spaced in a line. The seismic energy source was a Bison top and adjacent to the Tertiary volcanics of the upper EWG-3 elastic wave generator, with an accelerated portion of the Jornada Horst. Geologic interpretation of weight drop of 550 pounds. the seismic profiles in this report modifies the geologic The seismic reflection surveys were designed to interpretation of the contract geophysicists in that (1) focus on a depth of about 1,200 feet (Moriarty, 1992). the base of the upper Santa Fe Group in this report does Field and recording parameters included the following: not coincide with the gamma-ray log pick used by the (1) Six geophones were spaced in line 8 feet contract geophysicists and (2) the base of the upper apart for each recording channel, and the Santa Fe Group is assumed to coincide with the top of group interval was 50 feet. the Tertiary volcanics. (2) Shot points were located 100 feet apart in The interpreted seismic reflection profiles line, providing a 1,200-percent common (A-A', B-B', C-C', and D-D') were transformed to depth point stack. geologic sections (figs. 9A-C and 1OA) by using a (3) A split spread (24 channels on each side of velocity-conversion function developed by Reynolds the shot point), with a two-station gap, (1989) for the Jornada del Muerto Basin. This velocity resulted in a maximum offset of 1,250 feet. function was calculated by correlating seismic (4) The record length was 2 seconds, with a horizons on the profiles to the base of the sampling interval of 2 milliseconds.

27 WEST EAST

Datum is sea level Geology modified from 0.5 1 MILE EXPLANATION Reynolds, 1989 ______I_____ j FAULT-Arrow shows 0.5 1 KILOMETER relative movement

Figure 9A.--Geologic sections derived from interpreted seismic profiles located perpendicular to the axis of the Jornada Horst. Trace of section show in figure 8. WEST o EAST 0

OB 0) 5 B' B m i- c Jornada fault zone o r^,000' X d X LJJ STATION NUMBER Land 300 350 surtace 400 450 ^°u 4,500'n . 150 200 250 , i / i *- -4,500' - 0 JJP______ui_____ '" Upper banta he uroup \ Upper Santa 4,000'- J L "^tertiary volcanics \ eQrouP -4,000' - - -" I Upper Santa Fe Group \\ /I Tertiary volcanics ^ "~" \\\ 1 V 3,500'- - -^~ """""" Prp-T(3rtiary \ -3,500' ~ \ leniary \ volcanics nnn' - JORNADA FAULT !ONE 3 , \j\j\j a,uuu Datum is sea level Geology modified from 0 0.5 1 MILE Reynolds, 1989 i i Til 0 0.5 1 KILOMETER

Figure 9B.-Geologic sections derived from interpreted seismic profiles located perpendicular to the axis of the Jornada Horst. Trace of section shown in figure 8--Continued. WEST EAST

4,500' n STATION NUMBER 0 5p y surface ^^^^ MMHM Upper Santa Fe Group 4,000'- -4,000'

Tertiary ff volcanics 3,500'- -3,500'

Pre-Tertiary

3,000' Geology modified 3,000' Datum is sea level from Reynolds, 1989 0.25 0.5 MILE i I 0.25 0.5 KILOMETER Figure 9C.--Geologic sections derived from interpreted seismic profiles located perpendicular to the axis of the Jornada Horst. Trace of section shown in figures-Concluded. '

D D'

Land STATION NUMBER surface 4 ' 50 °'l280 r 4,500' 250 200 150 100 50 i Upper Santa Fe Group Upper Santa Fe Group 4,000'- 1-4,000' i-

3.500'H Tertiary 3,500' ~ volcanics

3,000'- H3.000'

2,500' ,500' Datum is sea level Geology modified EXPLANATION from Reynolds, 1989 0.25 0.5 MILE i i i FAULT-Arrow shows 0 0.25 0.5 KILOMETER relative movement

Figure 10A.--Geologic sections derived from interpreted seismic profiles located parallel to the axis of the Jornada Horst. Trace of section shown in figure 8.

30 E'

STATION NUMBER

420 400 380 360 340 320 300 280 260 240 220 200 180 160 140 120 101 4,500' I I ' ' ' I I ' ' ' ' I I I ' l - ' 4,500'

Upper Santa Fe Group Upper Santa Fe Group 4,000'-^ 4,000'

3,500'- 3,500'

Pre-Tertiary 3,000'- 3,000' Datum is sea level 0.25 0.50 MILE Geology modified from Moriarty, 1992

I 0 0.25 0.50 KILOMETER

EXPLANATION | FAULT

Figure 10B.--Geologic sections derived from interpreted seismic profiles located parallel to the axis of the Jornada Horst. Trace of section shown in figure 8--Continued. F' o 6 Land EXXON BEARD o § OLE FED. surface No. 1 WELL CD STATION NUMBER CO 4,500' I i 4,500' 101 120 140 160 180 200 i_ I I j h

Upper Santa Fe Group 4,000' 4,000' Lower Santa Fe Group

3,500' 3,500'

Pre-Tertiary 3,000' 3,000' Datum is sea level Geology modified from Moriarty, 1992 0.25 0.5 MILE

0.25 0.5 KILOMETER

EXPLANATION

/ FAULT

Figure 10C.--Geologic sections derived from interpreted seismic profiles located parallel to the axis of the Jornada Horst. Trace of section shown in figure 8--Concluded.

32 (5) The processing datum selected was an RESULTS OF SEISMIC REFLECTION altitude of 4,300 feet above sea level. SURVEYS (6) For control, the lines were surveyed and tied to unmarked survey monuments using Moriarty (1992) integrated the data bases from estimated altitudes from 1:24,000-scale his 1992 survey and Reynold's 1989 survey, but did not topographic maps. reinterpret the Reynolds (1989) data base. The deeper Seismic processing was completed by H.T. seismic horizon Moriarty selected was a basis for the Geophysical of Denver, Colorado. The processing geologic sections of lines E-E' and F-F'. A colored sequence included demultiplexing; trace editing; seismic section of the amplitude envelope trace geometry application; array simulation; spherical attribute was used to follow the faulting patterns to the divergence and attenuation compensation; pre- shallower altitudes in the Tertiary volcanics and the deconvolution muting; deconvolution, with surface Santa Fe Group (Moriarty, 1992). The thickness of the consistent spiking; datum and refraction statics Tertiary volcanic and volcaniclastic rocks, as reported application; common midpoint sort; spectral in the seismic reflection surveys in this report, may equalization; velocity analysis; surface consistent vary from 100 to more than 1,000 feet. residual statics; velocity analysis; surface consistent The eastern extent of the buried horst has been residual statics; normal moveout corrections; trim delineated by interpreted faults shown on profile A-A' statics; trace balance; common midpoint stack; spectral (fig. 9A) and profile B-B' (fig. 9B). The Jornada fault equalization; F-Y filter; bandpass filter; and trace zone, which defines the eastern extent of the buried balance (Moriarty, 1992). horst, was delineated by the seismic survey (fig. 11). The lengths and mean velocities for profiles E-E' Interpretation of the seismic profiles indicates that the and F-F' are: fault zone consists primarily of two normal faults whose traces trend north-northwest; the westernmost Mean velocity fault dips eastward from station 780 on profile A-A' Length of of surface Mean velocity of and from station 225 on profile B-B'; and the Seismic Number of profile (weathering) layer subweathering layer easternmost fault intersects profile A-A' at station 822 profile shot points (miles) (feet per second) (feet per second) and profile B-B' at station 272 (Reynolds, 1989). The easternmost fault was interpreted to be nearly vertical, E-E' 325 3.07 3,200 11,000 F-F' 100 0.94 3,200 11,000 to have the greatest vertical displacement, and was presumed to be the master fault in the fault zone. The interpreted seismic reflection profiles (E-E' and The western extent of the horst is probably F-F') were transformed to geologic sections (figs. 10B farther west of the study area. The throw of the fault and C). interpreted on profile A-A' at station 65 (fig. 9A) is only about 200 feet on top of the Tertiary volcanics and is too small to be the master fault. Thus, constraints on Data Interpretation the western extent of the horst have been determined in that the master fault(s) for the Jornada Horst is west of Due to the long offsets (1,250 feet) and the long the study area. shot point interval (100 feet), the shallow layer with a weathering velocity of about 1,700 to 2,300 feet per To determine the geometry and altitude of the top second (measured in the previously collected profiles; of the horst, the geologic sections derived from the Reynolds, 1989) was not detected during this survey, interpreted seismic profiles (figs. 9 and 10) were used thus the opportunity to delineate shallow seismic to pick the top of the Tertiary volcanics for each shot horizons was hampered. Because the continuity of the point; the resultant contour map is shown in figure 11. shallow reflectors was difficult to pick with confidence, The top of the horst, as depicted from the interpreted Moriarty (1992) selected a deeper seismic horizon as a seismic profiles, has an irregular surface that has been basis for mapping. According to Moriarty "... the shaped by a number of faults trending north-northwest deeper horizon was then 'projected' to shallower (fig. 12). elevations."

33 106°45' 106°37'30" 21

32° 25'

STUDY T. AREA 22 BOUNDARY S.

T. 23 S.

32° 17' 30"

R.1 E. R.2E. R.2 E. R.3 E. Base map from USGS digital data, 3 MILES scales: 1:100,000 and 1:500,000 Geology from Moriarty, 1992 3 KILOMETERS

EXPLANATION

^3900 v ALTITUDE OF HORST-Dashed FAULTS--U, upthrown side; x where approximate. Interval, D, downthrown side in feet, is variable. Datum is sea level

Figure 11 .--Altitude of the top of the Jornada Horst Tertiary volcanics, as determined from the seismic surveys. 34 WEST EAST

SAN AUGUSTIN PASS ' FEET

-5,500

-5,000

FLUVIAL FACIES -4,500

FLOOD-PLAIN BEDROCK x DEPOSITS Upper Santa Fe Group / \~v(pALEOZOIC \ A ~ < AND

// / **' TERTIARY)" - / -4,000

3,500- ALLUVIAL-FAN -3,500 FACIES JOBNADA/' -* HQRST. - '_ O '"- O ' x - O ' x - 3,000 3,000 Datum is sea level

[^-APPROXIMATE EXTENT OF STUDY AREA"+\ EXPLANATION 0__1 234 SMILES FAULT-Arrow shows 01234 5 KILOMETERS relative movement

Figure 12.--Buried horst along U.S. Highway 70, as interpreted from the seismic profiles. The highest parts of the horst appear to be at Mountain and that the top of the horst is above the altitudes of about 4,040 feet at station 160 and about water table and acts as a subsurface flow barrier north 4,070 feet at stations 270 and 280 on profile E-E' of U.S. Highway 70. (fig. 10B). Between those highs is a low area at an altitude of about 3,920 feet at stations 210 and 220 (fig. 10B); this interpreted low area on the horst directly SUMMARY AND CONCLUSIONS underlies the Las Cruces Arroyo North Fork (pi. 1). Another low area is suggested by the interpreted Available data indicate that little or no ground seismic sections at an altitude of 3,910 feet at station water flows from the Jornada del Muerto ground-water 360 on profile E-E' (fig. 10B); this interpreted low area basin to the Mesilla ground-water basin over some on the horst directly underlies Alameda Arroyo (pi. 1). portions of the Jornada Horst. However, some ground However, the genesis for these low areas cannot be water flows through the upper Santa Fe Group deposits determined with existing information, and the low above the horst. Six seismic reflection profiles were areas cannot be concluded to be incised channels. In collected in the vicinity of the Jornada Horst between fact, an argument could be made that the subsurface Goat Mountain and Tortugas Mountain near Las lows shown on the seismic sections are artifacts of Cruces, New Mexico, to determine more precisely the invalid assumptions made in the processing of field geometry of the horst and to determine whether large, records the weathering layer velocities and thicknesses used in processing may not have been buried channels have been incised into the top of the properly adjusted to account for the different surficial horst. Incised, buried channels, if present on the horst, materials associated with existing arroyos. could be filled with alluvial material with higher To understand better the potential effect of the hydraulic-conductivity values than those of the Jornada Horst on regional ground-water flow, the material in the horst. Incised, buried channels would interpreted altitude of the top of the horst (from the allow ground water to readily move from the Jornada seismic profiles) has been compared to the water-table del Muerto ground-water basin to the Mesilla ground- altitudes in the area (from Wilson and others, 1981). water basin. Ground-water-level data for selected wells and test The upper part of the Jornada Horst is composed holes near the study area are compiled in table 2. The of Tertiary volcanic and volcaniclastic rocks; these resulting map (pi. 1) projects the top of the horst to be rocks overlie Permian sedimentary rocks. The horst, in higher than the water table in three areas: north of turn, is overlain by unconsolidated sediments of the Alameda Arroyo, extending north of U.S. Highway 70; upper Santa Fe Group as thick as at least 250 feet. between Alameda Arroyo and the Las Cruces Arroyo Ground-water flow immediately east of the horst near North Fork; and a small area between the Las Cruces U.S. Highway 70 is deflected northward in the southern Arroyo North and South Forks. Although seismic Jornada del Muerto ground-water basin presumably control on the highest part of the horst does not extend because of the change from higher hydraulic- north of U.S. Highway 70, the horst probably remains conductivity values of the aquifer materials in the higher than the water table north of the highway; this southern basin to lower hydraulic-conductivity values would account for the apparent "damming" of ground of the materials in the horst. water and the low gradient of the water table east of the horst and north of the highway (pi. 1), as discussed The gross geometry of the horst-eastern extent, previously. constraints on the western extent, and general altitude In summary, the gross geometry of the horst~the of the top was discerned by interpretations of the eastern extent, constraints on the western extent, and seismic profiles. The presence or absence of large general altitude of the top was discerned by channels incised into the top of the horst could not be interpretations of the seismic profiles. The presence or confirmed by those interpretations. However, the absence of large channels incised into the top of the seismic interpretations suggest that the water table is horst could not be confirmed by those interpretations. above the top of the horst for most of its extent between The seismic interpretations however, do suggest that U.S. Highway 70 and Tortugas Mountain and that the the water table is above the top of the horst for most of top of the horst is above the water table and acts as a its extent between U.S. Highway 70 and Tortugas subsurface flow barrier north of U.S. Highway 70.

36 Table 2.--Well-construction and water-level data for selected wells and test holes near the study area [ , no data; R, recently pumped well; P, pumping