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Subsurface in the Southern San Luis Basin, New Mexico P. Drakos, J. Lazarus, J. Riesterer, B. White, C. Banet, M. Hodgins, and J. Sandoval, 2004, pp. 374-382 in: Geology of the Taos Region, Brister, Brian; Bauer, Paul W.; Read, Adam S.; Lueth, Virgil W.; [eds.], New Mexico Geological Society 55th Annual Fall Field Conference Guidebook, 440 p.

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PAUL DRAKOS1, JAY LAZARUS1, JIM RIESTERER1, BILL WHITE2, CHRIS BANET2, MEGHAN HODGINS1, AND JOHN SANDOVAL2 1Glorieta Geoscience Inc. (GGI), PO Box 5727, Santa Fe, NM 87502 2US Bureau of Indian Affairs (BIA), Southwest Regional Office, 615 First St., Albuquerque, NM 87102

ABSTRACT.—Subsurface lithologic and geophysical data from a series of municipal, exploratory, subdivision, and domestic wells are used to delineate variations in thickness and extent of Tertiary through Quaternary sediments and basalt flow sequences in the southern San Luis Basin. Servilleta basalts increase in thickness from south to north within the Taos Valley; they are absent in BOR1, present as a single thin flow in BOR3, and present as three multiple-flow sequences at BOR4, K3, RP2500, and the Airport well. The Ojo Caliente Member varies in apparent thickness from thin or absent at BOR1 and BOR2/3 to greater than 1000 ft (300 m) at RP2500 to 340 ft (100 m) at the Airport well. The apparent thickness of the Ojo Caliente is greatest along the Rio Pueblo, suggesting deposition in a depression, possibly an ancestral Rio Hondo or Rio Pueblo drainage, during mid-to-late-Miocene time. The Ojo Caliente sand may have been derived from the west, accumulating against Chama-El Rito alluvial fans building off the eastern mountain front. Data from the drilling program are also used to identify and constrain offset on several intrabasin faults and a mountain front graben bounded on the west by the Seco Fault, across which the Servilleta Formation is offset 950 ft (290 m), and on the east by the Town Yard fault. The average subsidence rate within the graben is estimated as approximately 0.1mm/yr (0.3 ft/1000yr). Down-to-the west offset across the Town Yard Fault is > 1390 ft (420 m).

INTRODUCTION per), are used to identify lithologic and geophysical signatures of the basin-fill units. These data are utilized to determine which Subsurface data collected from drilling programs conducted each well is completed into, and are used to during the past 15 years are utilized to evaluate the subsurface explore the stratigraphic framework and shallow structures of the stratigraphy in the southern San Luis Basin. Of particular impor- Taos Valley. tance are a series of exploratory wells drilled to depths ranging from 1000 ft (300 m) to 2990 ft (910 m) below ground surface GEOLOGIC SETTING (bgs), as part of a cooperative exploratory drilling program con- ducted by the Town of Taos and Taos Pueblo, with funding from The study area is situated in the Taos Valley within the south- the US Bureau of Reclamation (BOR). Data from the drilling ern San Luis Basin (Fig. 1). The San Luis Basin is situated in the program were compiled, and preliminary correlations were made northern Rio Grande rift, a generally north-south trending series between deep wells to provide a stratigraphic framework for an of fault-bounded basins extending from Colorado to Mexico evaluation of the hydrology of the basin fill aquifer system (see (Hawley, 1978; Chapin and Cather, 1994). Rifting in the San Drakos et al., 2004, this volume). The area of this study includes Luis Basin dates from approximately 30-27 Ma and has resulted the region between the Sangre de Cristo mountain front on the in approximately 8-12% extension, primarily along north-south east and the Rio Grande on the west, the Rio Hondo on the north trending, down to the west normal faults (Tweto, 1979; Brister and the Rio Grande-Rio Pueblo de Taos confluence on the south and Gries, 1994; Chapin and Cather, 1994; Kluth and Schafte- (Fig. 1). naar, 1994). The southern San Luis Basin in the vicinity of Taos is a deep graben with predominant down-to-the-west faulting along METHODOLOGY the east margin (Bauer and Kelson, 2004, this volume). In the San Luis Basin near Alamosa, Tertiary and Quaternary sedimentary Numerous studies (e.g. Baldridge et al., 1984; Dungan et al., deposits exhibit average dips of 0° to 12° to the east (Chapin and 1984; Lipman and Mehnert, 1979) have defined syn-rift Ter- Cather, 1994). tiary sedimentary and volcanic units in the general vicinity of the study area. Well log data from this study, particularly from DESCRIPTION OF STRATIGRAPHIC UNITS several deep exploratory and production well borings, are used to constrain the subsurface extent of and relationships between From oldest to youngest, the units underlying the basin dis- rift-related sedimentary and volcanic units. Because the subtle cussed in this study are: 1) Pennsylvanian Alamitos Formation, differences between basin-fill units can be difficult to discern in 2) Tertiary Picuris Formation, 3) Tertiary , 4) Ter- drill cuttings and due to the relative paucity of data points, the tiary Servilleta Formation, and 5) Quaternary Alluvium. Galusha stratigraphic inferences and subsurface correlations presented in and Blick (1971) subdivided the Santa Fe Group in the Española this paper are preliminary. Data from thirteen wells greater than Basin into the and the overlying Chamita 1000 ft (300 m) deep, including lithologic logs of cuttings and Formation. The Tesuque Formation is further subdivided into the geophysical logs (electric logs, neutron, natural gamma, and cali- Chama-El Rito Member and the overlying Ojo Caliente Sandstone SUBSURFACE STRATIGRAPHY IN THE SOUTHERN SAN LUIS BASIN 375

Symbol Explanation Colorado Plateau SL R Major stream or river io Hondo Study Area 1 0 1 Miles Jemez y Mountains Volcanic 1 0 1 Kilometers Field . 150 E State Rd. 68 Hwy

Southern Rock

A US Hwy 64 Jemez Lineament Great Plains

S Mogollon - Datil Volcanic Field US Hwy 64 aos de T io Grande Rift blo P R ue Rio Grande P Town of io R Taos M 68

State Rd. Sangre de Cristo Mountains Kilometers Study Area Detail FIGURE 1. Location map – schematic map of New Mexico showing study area and the approximate limits of various physiographic provinces and geographic features. Major basins in the Rio Grande rift from north to south are: SL=San Luis, E = Española, A = Albuquerque, S = Socorro, P = Palo- mas, M = Mimbres. (state map modified from Sanford et al., 1995 and Keller and Cather, 1994).

Member (Fig. 2; Galusha and Blick, 1971). Although extending tan, white, and brown fine-grained sandstone beds and shale beds, this Santa Fe Group stratigraphic nomenclature into the south- with limestone beds representing approximately 50% of the pen- ern San Luis Basin may be problematic, it is used as an initial etrated section. The shallow depth at which the Paleozoic section framework for this investigation. Some revision of stratigraphic was encountered in the Town Yard well is attributed to offset on units may be required as additional surface and subsurface data the Town Yard fault (Figs. 3 and 4; Drakos and Lazarus, unpubl. become available. report to the Town of Taos 1997; Bauer et al., 1999; Drakos et Along the basin margin on the east side of the study area, al., 2001). the Tertiary deposits are in fault and depositional contact with older sedimentary and crystalline rocks within the Sangre de Picuris Formation (Tp) Cristo Mountains. While not discussed in detail in this paper, the crystalline rocks include Proterozoic plutonic and gneissic The oldest Tertiary unit encountered is the Oligocene to Mio- complexes in the Taos Range in the northern part of the study cene Picuris Formation, which is penetrated in the BOR2 deep area, and metasedimentary rocks (quartzite, schist, and phyllite) piezometer and the BOR3 production well (located at the same in the northern Picuris Mountains located in the southern part of site, 36 ft [11 m] from one another) (Fig. 4; Drakos et al., unpubl. the study area (Bauer et al., 1999). Paleozoic sedimentary rocks report to the Town of Taos, 2002). The Picuris Formation is sub- overly the metasedimentary rocks in the southern portion of the divided into an upper fine-grained, ash-rich member and a gen- study area, south of the Rio Pueblo de Taos, and includes the erally coarser-grained lower member that includes a distinctive Pennsylvanian Alamitos and underlying Flechado Formations. quartzite-rich basal conglomerate (Bauer et al., 1999). The upper The Flechado Formation is comprised of a clastic-dominated and lower members are separated by the Llano Quemado volca- sedimentary section (shale, siltstone, sandstone, and conglomer- nic breccia, clasts of which have been dated to 28.4 Ma (Bauer et ate beds) and is overlain by the more limestone-rich Alamitos al., 1999). The upper Picuris Formation is composed of predomi- Formation (Bauer et al., 1999). nantly volcanic clasts and grains and is interpreted to be derived from pre-rift and early rift volcanic centers in the San Juan volca- Alamitos Formation (&a) nic field to the north and northwest. It is inferred that the Picuris Formation was encountered in One well in the study area (Taos Town Yard) penetrated lime- well nest BOR2/3 from 1810 to 2110 ft (552 to 643 m) bgs. At the stone of the Pennsylvanian Alamitos Formation at a depth of BOR2/3 well nest, the Picuris Formation comprises fine-grained 720 ft (220 m) below ground surface (bgs) (Drakos and Lazarus, silty sediments with minor reworked ash from 1810 to 1945 ft unpubl. report to the Town of Taos, 1997). In the Town Yard well (552 to 593 m) bgs overlying interbedded coarse sandy gravel, the Alamitos Formation consists of interbedded gray limestone, including clasts of pink, white, and green quartzite, fossiliferous 376 DRAKOS ET AL.

Ma PERIOD STRATIGRAPHIC UNITS Chama-El Rito Member of the Tesuque Formation (Ttce) Holocene Five wells in this study are completed primarily in the Chama- 0.01 - El Rito Member of the Tesuque Formation. The Chama-El Rito late Member consists of subequal proportions of interbedded con- 0.25 - QUATERNARY Qal - alluvium glomerate and sandstone, with minor mudstone beds (Steinpress, Pleistocene middle 1981; Bauer and Kelson, 1998). Conglomerate beds contain a 0.7 - predominance of volcanic clasts with subordinate early granitic and quartzite clasts. Locally (in the vicinity of BOR2/3), 1.6 - NW Lama Fm. SE volcanic clasts are subordinate to sedimentary clasts. This is Upper basalt interbedded interpreted to be the result of locally uplifted Paleozoic strata that Pliocene Servilleta Middle basalt Fm. sediments provided a proximal source of coarse material. The Chama-El Lower basalt Rito Member has a thickness of up to 1575 ft (480 m) (Bauer and 5.3 - Chamita Fm. Kelson, 1998). e Group

Ojo Caliente Ojo Caliente Sandstone Member of the

Santa F member Miocene Tesuque Tesuque Formation (Ttoc) Fm. Chama- El Rito member Five wells in the study area are completed primarily in the Ojo TERTIARY Caliente Sandstone Member of the Tesuque Formation (well nests Upper at RP2000/RP2500 and at BOR4/BOR6 are considered as single 23.7 - member wells for this study). The Ojo Caliente Sandstone Member is a Llano Quemado breccia buff to light brown, fine to very fine-grained, poorly consolidated Picuris Fm. eolian sandstone with large-scale tabular cross-beds (Bauer and Oligocene Lower member Kelson, 1998). While the Ojo Caliente is absent at the BOR2/3

Lower member location, it is identified in both drill cuttings and geophysical logs conglomerate at the Airport well and the RP2500 well. At RP2500, the Ojo 36.6 - Caliente is differentiated from the overlying Chamita Formation Eocene on the basis of sorting and grain size. Fine-grained, well-rounded, 57.8 - well-sorted, unconsolidated tan sand with moderate oxidation and Paleocene a distinct geophysical signature (relatively low-API gamma ray 66.4 - log values and generally parallel 16” and 64” resistivity logs; Fig 6) was encountered from 1305 ft to 2527 ft (398 to 770 m) bgs. 245 - Reddened layers overlying carbonate horizons, apparent Bt-Bk soil horizons, and intervals containing carbonate nodules were Sangre de Cristo Fm. Lower (may not exist in study area) also observed during drilling in this interval. A well-developed

286 - soil with Bt and Bk horizons encountered between 1305 and 1315 Madera Fm. ft (398 to 401 m) bgs is interpreted to mark the top of the Ojo upper arkosic Alamitos limestone Caliente. Based on subsurface data, the Ojo Caliente Sandstone PENNSYLVANIAN Upper Fm. member equivalent Member varies in thickness from thin or absent on the south end of the Taos basin (BOR2/3) to greater than 1000 ft (305 m) along the Rio Pueblo de Taos (RP2500) to 340 ft (104 m) at the Taos Madera Fm. lower Middle gray limestone Airport. Flechado equivalent Fm. Sandia Fm. Lower equivalent Chamita Formation (Tc)

(modifiedFIGURE 2. Taos from Valley Bauer Stratigraphic et al., Nomenclature 1999) (modified from The Tesuque Formation is overlain by the Miocene - Pliocene Bauer et al., 1999) Chamita Formation (Fig. 2), which was originally defined in the Española Basin as the uppermost formation in the Santa Fe Group limestone and sandstone, and clayey silt with reworked ash layers (Galusha and Blick, 1971). In the study area, the Chamita Forma- (?) from 1945 to 2110 ft (593 to 643 m) bgs, the total depth of tion consists of moderately to poorly sorted sandstone beds with the well. Based on the quartzite-rich gravel penetrated near the clasts of intermediate volcanic rock, quartzite, and other meta- bottom of the BOR2/3 wells, the lower stratigraphic sequence morphic rocks (Bauer and Kelson, 1998). At locations where the encountered is interpreted to be the lower Picuris Formation and Ojo Caliente Sandstone Member is absent, it is difficult to differ- the upper Picuris Formation is absent (Fig. 4). entiate the Chamita Formation from the Chama-El Rito Member SUBSURFACE STRATIGRAPHY IN THE SOUTHERN SAN LUIS BASIN 377 of the Tesuque Formation in drill cuttings. Similarly, where the distinctive weathered mud flow deposits observed in samples Servilleta Formation (see below) is absent, it is also very difficult from boreholes and along Blueberry Hill road on the west side of to determine the contact between the Chamita Formation and the Taos that have been referred to as the Blueberry Hill mudflows overlying Lama formation. Based on Glorieta Geoscience Inc. (Sorrel and Banet, unpubl. BIA Report, 1993). The Lama forma- subsurface lithologic and borehole geophysical data (Drakos and tion is likely correlative with the Plio-Pleistocene Ancha Forma- Hodgins, unpublished report to the Town of Taos, 2001; Drakos et tion, previously identified in the Española Basin (Galusha and al., unpublished report to the Town of Taos, 2002) and thickness Blick, 1971; Koning et al., 2002; Spiegel and Baldwin, 1963). estimates from Bauer et al. (1999), Chamita Formation thickness Because the Lama formation is indistinguishable from Quater- ranges from 0 (at BOR 2/3) to 890 ft (271 m) at RP2500. The nary alluvium in drill cuttings and has been inferred at only one well log from RP2500 shows that the Chamita Formation may location based on geophysical logs (BOR 5; Drakos et al., 2001) interfinger with the underlying Ojo Caliente Sandstone Member the Lama formation is grouped with overlying alluvial deposits in at that location. this study. Total thickness of alluvium (± Lama formation) over- lying the Servilleta Formation ranges from less than 100 ft (30 Servilleta Formation (Ts) m) at Colonias Point to approximately 1500 ft (460 m) at BOR5 (Figs. 3 and 4). Interbedded basalt flows and sediments comprise the Servil- leta Formation, which underlies either Quaternary alluvial depos- DISCUSSION its or the Lama formation, where present. Some previous workers (Dungan et al, 1984; Lipman and Mehnert, 1979) have separated Subsurface Correlations and Interpretations Based the basalt flows and sediments into separately named units, while on Well Log Data other researchers (e.g. Lambert, 1966) have grouped the inter- bedded sequence of three basalt units and sediments together as Lithologic and geophysical data from the Town wells (RP2500, the Servilleta Formation. For purposes of this study, the Servil- RP2000, BOR2, BOR3, and the Taos Town Yard Exploratory leta Formation is treated as a single unit that comprises up to Boring) and the BIA wells (BOR4/BOR6, BOR-5, BOR7, and three basalt flow members, each consisting of one or more indi- K2/3) were used to delineate variations in thickness and extent vidual flows (where present), interbedded sediments, fine-grained of the basalt flows of the Servilleta Formation and underlying sediments at the top of the Servilleta Formation above the upper Tertiary basin fill sediments in the Taos area of the southern San basalt flow member, and the baked zone (generally red clay) Luis Basin (Figs. 4 and 5). The cross sections were constructed below the lower basalt flow member. The basalts are interlay- based on correlations from geophysical logs and from lithologic ered with gravel, sand and clay of mixed metamorphic, igneous descriptions (Fig. 6). and volcanic , with predominantly quartzite clasts. The Servilleta basalts increase in thickness from south to north sediments between the upper and middle Servilleta basalt flows within the Taos Valley; they are absent in BOR1, present as a include a fluvial deposit of rounded sand and quartzite-dominated single thin flow in BOR3, and present as three multiple-flow gravel approximately 40 ft (12 m) thick that, together with frac- sequences at BOR4, K3, RP2500, and the Airport well. Servilleta tured basalt at some locations, are a thin but moderately produc- basalts can be traced eastward in BIA wells K3, Tract B Tip site tive aquifer referred to informally as the “Agua Azul” aquifer (BOR4/BOR6), and BOR5, where the upper Servilleta basalt is (Drakos and Lazarus, 1998). The basalt flows range in age from downdropped approximately 950 ft (290 m) within a mountain 2.8 to 4.8 million years (Appelt, 1998; Lipman and Mehnert, front graben, which is bounded on the west by the Seco fault and 1979; Manley, 1976). The thickness of the entire Servilleta For- on the east by the Town Yard fault (Fig. 3). The average sub- mation (basalt flows and sediments included) ranges from 0 to sidence rate within the graben is approximately 0.1mm/yr (0.3 650 ft (198 m) (Dungan et al., 1984), with thinning/pinching out ft/1000yr) based on an age of approximately 3 Ma for the upper towards the Sangre de Cristo mountain front to the east and the Servilleta basalt (Appelt, 1998). This subsidence rate is similar Embudo fault zone to the south. to the slip rate along the nearest segment of the Mountain Front fault calculated by Menges (1988, 1990). Down-to-the west offset Quaternary Alluvium (Qal) across the Town Yard Fault is > 1390 ft (420 m), based on the depth at which Paleozoic sedimentary rocks were encountered in Alluvium overlying the upper Servilleta basalt flow member the Town Yard well (720 ft or 220 m), and the absence of pre-Ter- includes Quaternary alluvial-fan deposits that interfinger with tiary sediments in BOR3, drilled to a depth of 2110 ft (640 m). fluvial deposits of the Rio Grande, Rio Hondo, and Rio Pueblo In the majority of wells drilled to date, Tertiary fluvial sedi- de Taos stream systems. The high terrace surfaces throughout ments appear to show small and large scale fining upward the Taos basin record the culmination of aggradation along the sequences, indicating deposition in an environment relatively free Rio Grande during the Middle Pleistocene (Pazzaglia and Wells, of tectonic influences. However, sediments in BOR3 and BOR5 1990). The Plio-Pleistocene rift fill sequence underlying younger are generally much coarser grained and appear to show small and alluvium in the Taos basin has been informally named the Lama large scale coarsening upward sequences, indicating that deposi- formation (Pazzaglia and Wells, 1990) or has been included as part tion may have been controlled by motion on the Town Yard and of the Chamita Formation (Bauer et al., 1998). This unit includes Seco faults (Figs. 3, 4, and 5). 378 DRAKOS ET AL.

Symbol Explanation Unconfined Alluvial Well Leaky-confined Alluvial Well Rio Ho Agua Azul Well ndo Ojo Caliente + Chamita Well Chama-El Rito Well Fault, inferred from surface or drilling data, ball and bar on downthrown side Mariposa Ranch Anticline E

Syncline 150 ? ro 522 e 3 c Major road u L Major stream or river io R Arch AA' Line of cross-section shown ? in Figures 4 and 5 Gorge

? BOR 4,6 BOR 5 Kilometers B'

Go ?

?

r D t g Colonias Point

e B ul TOT Airport a

F

o a S

A 64 c u e

e d F

l c t Los Cordovas Fault Zone S Fo ar

Y o

y a n o u r w os r lt Ta o o de ? l A T b Pue io R

K3

e

n

o

Z

t l

u ando de a rn F Fe Ta io o o R s 64 t

is ? r Rio Grande C' E' BOR 2B D' Town Yard e C C d ? BOR 3 e r

t g l n u RP2500 a ? a S F ?

d r

a s R o Y a i o T n ? de G w lo o b 68 r e a T n u ? P d io A' e R BOR1 d el

R a n c ? h o

Map grid, NAD 1927, UTM Zone 13, meters

FIGURE 3. Map of study area showing cross section locations SUBSURFACE STRATIGRAPHY IN THE SOUTHERN SAN LUIS BASIN 379

N A-A' S Taos Airport (7063') BOR1 (6955') Qal Tusb Ts RP2500 (6665') Ts Tmsb Qal

Ts Tlsb Ttoc and Tc Ttce Tc

} Tc or Ttoc 1720' TD Ttoc Ttoc Ttce 2003' TD See Figure 3. for cross section line locations 2500' TD W B-B' E Taos Airport BOR6 BOR5 (7063') (7247') Legend Ts (7188') Qal: Undifferentiated Quaternary alluvial deposits Qal Tusb Tusb: upper Servilleta Basalt Tmsb Tmsb: middle Servilleta Basalt

Tlsb Seco Fault Qal Tc Tlsb: lower Servilleta Basalt Ts Ts: Servilleta Formation Ttoc Ttoc sediments & Ttce Tgu: Undifferentiated Tertiary Tusb sediments 1720' TD 2020' TD 1763' TD Tc: Chamita Formation W C-C' E Ttoc: Ojo Caliente Sandstone of RP2500 BOR2,3 (6868') Tesuque Formation (6665') Tusb Qal Qal Ttoc & Ttce: Interbedded Ojo Tmsb Tlsb Caliente and Chama El Rito Members of Tesuque Ts Ts Tlsb Formation

lt IPls Ttce: Chama El Rito Member of Tc Tgu Tesuque Formation Taos Town Yard Tp: Picuris Formation (6955') IPls: Paleozoic Limestone

own Yard Fau Ttce T 1020' TD (Alamitos Formation ?) 500 Tp 100

Ttoc 2109' TD meters Feet 4000 1000 2500 ' TD Vertical Exag. = 8.4x

FIGURE 4. Cross sections through selected Taos area wells 380 DRAKOS ET AL.

Eolian sand of the Ojo Caliente Sandstone Member of Tesuque east by the Town Yard fault. The Town Yard fault projects into the Formation is the most distinctive sedimentary unit in the basin present day Rio Lucero drainage, and the Seco fault projects into and is identifiable in both well cuttings and geophysical logs the Arroyo Seco drainage. The Town Yard fault was identified by (Fig. 6). The apparent thickness of the Ojo Caliente is greatest drilling into the Paleozoic sedimentary rocks at the Town Yard along the Rio Pueblo de Taos, suggesting deposition in a depres- well at 720 ft, whereas the nearby BOR3 well was drilled to a sion, possibly an ancestral Rio Hondo or Rio Pueblo, during total depth of 2100 ft entirely in basin fill deposits. mid-to-late-Miocene time. The Ojo Caliente sand may have been Stratigraphic nomenclature developed for Tertiary sedimen- derived from the west, accumulating against the Chama-El Rito tary deposits in the Española Basin by Galusha and Blick (1971) (see above) alluvial fans building off the eastern mountain front. is utilized for this study; however, revision of stratigraphic This would account for the interfingering of these two members units may be required after additional surface and subsurface observed in BOR6 and BOR1 (Figs. 4 and 5). data become available. An eolian deposit interpreted as the Ojo Caliente Sandstone Member of Tesuque Formation was identi- CONCLUSIONS fied in cuttings and geophysical logs from several wells in the basin, where it ranged in thickness from thin or absent at BOR2/3 Data from the drilling program helped to identify and con- to greater than 1000 ft (305 m) along the Rio Pueblo de Taos strain offset on several intrabasin faults. Servilleta basalts can be (RP2500) to 340 ft (104 m) at the Taos Airport. The apparent traced eastward in BIA wells K3, Tract B Tip site (BOR4/BOR6), thickness of the Ojo Caliente is greatest along the Rio Pueblo de and BOR5, where the upper Servilleta basalt is downdropped Taos, suggesting deposition in a depression, possibly an ances- approximately 950 ft (290 m) within a mountain front graben. tral Rio Hondo or Rio Pueblo, during mid-to-late-Miocene time. This graben is bounded on the west by the Seco fault and on the Where the Ojo Caliente is absent, identifying the contact between

N E-E' S Mariposa Ranch (7329') BOR6 Taos Town Legend (7188') Yard : Undifferentiated Quaternary K-3 (6925') (6955') Qal alluvial deposits Qal Qal Tusb: upper Servilleta Basalt Tmsb: middle Servilleta Basalt Tusb Ts Tmsb Ts Tlsb Tlsb: lower Servilleta Basalt lPls Tc Tc Ts: Servilleta Formation sediments ard Fault Ttoc + Ttce (?) Tgu: Undifferentiated Tertiary

Town Y sediments Ttce Tc: Chamita Formation Ttoc: Ojo Caliente Sandstone of Tesuque Formation N D-D' S Ttoc & Ttce: Interbedded Ojo Caliente and Chama El Rito BOR5 Members of Tesuque (7247') Formation

Ttce: Chama El Rito Member of K-3(6925') BOR2,3 Qal Tesuque Formation (fan deposits) Tusb Qal Tp: Picuris Formation IPls: Paleozoic Limestone Tmsb Ts (Alamitos Formation ?) Tlsb 500 Tc 100 Tc Tgu Seco Fault

meters Feet Tusb 4000 1000 Ttce Vertical Exag. = 8.4x

Tpu Tpl

FIGURE 5. Cross sections through selected Taos area wells SUBSURFACE STRATIGRAPHY IN THE SOUTHERN SAN LUIS BASIN 381

BOR-4 Airport K3 Town Yard Gamma Resistivity Gamma Resistivity Gamma Resistivity Gamma Resistivity 0 160 0 100 0 160 0 100 0 160 0 100 0 160 0 100

7000 Qal Qal Ts Tusb Qal Tusb Tusb Tmsb Tmsb Ts

6500 Ts

(feet) Tlsb Tlsb Ts Tlsb Ts Tc Tc Tc 6000

Elevation Ttoc Ttoc

ard Fault

Y

Ttce n

Ttce w + Ttoc To 5500 Ttce

lPls

Qal: Undifferentiated Quaternary alluvial deposits Ttoc: Ojo Caliente Sandstone of Tesuque Formation Gamma (API) Tusb: upper Servilleta Basalt Ttoc + Ttce: Interbedded Ojo Caliente and Chama Resistivity 16 Tmsb: middle Servilleta Basalt El Rito Members of Tesuque Formation inch (Ohm-m) Tlsb: lower Servilleta Basalt Ttce: Chama El Rito Member of Tesuque Formation Resistivity 64 Ts: Servilleta Formation sediements lPls: Paleozoic Limestone (Alamitos Formation?) inch (Ohm-m) Tc: Chamita Formation See Figure 3 for well locations

FIGURE 6. Correlation of units based on geophysical log interpretations

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APPENDIX A WELL LOCATIONS FOR TAOS AREA WELLS CITED IN THIS STUDY UTM NAD 27, zone 13, m. UTM NAD 27, zone 13, m. WELL NAME Easting Northing WELL NAME Easting Northing BOR2B/2C 446240 4026553 BJV #1 441230 4023480 BOR3 446247 4026541 BOR 1 442124 4022604 BOR5 447345 4035906 BOR 4 Deep 444766 4035805 BOR7 444280 4038930 BOR 6 #1 444797 4035805 K2 - K3 446688 4030429 BOR 6 #2 444797 4035805 RP 2000 Deep 440380 4026000 BOR2A 446247 4026541 RP 2500 440462 4026069 Town Taos Airport 439480 4034760 UNM/Taos 441310 4022260 Town Yard 447060 4026680