U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2016–5087

Hydrogeologic Investigations of the Miocene 

Nogales Formation in the Nogales Area, 

Upper Santa Cruz Basin, Arizona

Hydrogeologic Investigations of the 

Miocene Nogales Formation in the Nogales 

Area, Upper Santa Cruz Basin, Arizona

By William R. Page, Floyd Gray, Mark W. Bultman, and Christopher M. Menges

Scientific Investigations Report 2016–5087

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Director

U.S. Geological Survey, Reston, Virginia: 2016

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Suggested citation:

Page, W.R., Gray, Floyd, Bultman, M.W., and Menges, C.M., 2016, Hydrogeologic investigations of the Miocene 

Nogales Formation in the Nogales area, upper Santa Cruz basin, Arizona: U.S. Geological Survey Scientific 

Investigations Report 2016–5087, 31 p., http://dx.doi.org/10.3133/sir20165087.

ISSN 2328-0328 (online)
iii

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................1

Nogales Formation Stratigraphy, Structure, and Basin Geometry........................................................4

Stratigraphy ...........................................................................................................................................4

Proto Canyon Member................................................................................................................4

Nogales Wash Member..............................................................................................................4

Mariposa Member.......................................................................................................................4

Structure.................................................................................................................................................5

Basin Geometry.....................................................................................................................................5

Basin Evolution.............................................................................................................................5

Depth to Bedrock Maps..............................................................................................................6

Results of Porosity, Bulk Density, Saturated Hydraulic Conductivity, and Fabric Analyses for 

the Nogales Formation ....................................................................................................................6

Discussion of Analyses by Nogales Formation Member......................................................................10

Proto Canyon Member.......................................................................................................................10

Nogales Wash Member.....................................................................................................................14

Mariposa Member..............................................................................................................................16

Fractures in the Nogales Formation .........................................................................................................18

Summary........................................................................................................................................................22

Acknowledgments.......................................................................................................................................22

References Cited..........................................................................................................................................22

Appendix 1. Thin Section Analyses of the Nogales Formation.........................................................26

Appendix 2. Values of Bulk Density, Effective Porosity, and Saturated Hydraulic 

Conductivity For the Nogales Formation ....................................................................................28

Appendix 3. Porosity, Saturated Hydraulic Conductivity, and Bulk Density Analyses and 

Scanning Electron Microscope and X-Ray Diffraction Methods...........................................31

Figures

All photographs taken by the author unless otherwise noted.

1. Map of the upper Santa Cruz basin area, showing major physiographic, geologic,

and hydrologic features in the region .......................................................................................2

2. Map of the Rio Rico and Nogales (Arizona) 7.5’ quadrangles, showing major

physiographic, geologic, and hydrologic features in the study area...................................3

3. Depth to bedrock in the Rio Rico and Nogales (Arizona) 7.5’ quadrangles........................7

4. Locations of Nogales Formation samples analyzed in this study.........................................8

5. Cyclic fining-upward sequences in the lower part of the Proto Canyon member in

Proto Canyon ...............................................................................................................................11

6. Thin section of sandstone from the lower part of the Proto Canyon member at Proto

Canyon showing a predominantly pumice fragment matrix................................................11

7. Scanning electron microscope image of sandstone from the lower part of the Proto

Canyon member at Proto Canyon showing clinoptilolite in pore space............................12

8. Red and white gravelly claystone and overlying gray volcaniclastic sandstone beds

in the middle part of the Proto Canyon member in Yerba Buena Canyon .........................12
iv

9. Pinkish-gray volcaniclastic sandstone in the uppermost part of the Proto Canyon

member between Interstate 19 and Grand Avenue, north of Mariposa Road .................12

10. Scanning electron microscope image of sandstone from the uppermost part of the

Proto Canyon member between Interstate 19 and Grand Avenue, north of Mariposa

Road, showing clinoptilolite in pore space ............................................................................13

11. Fine-grained, moderately sorted volcaniclastic sandstone in the upper part of the

Proto Canyon member in the Sonoita Creek area.................................................................14

12. Scanning electron microscope image of sandstone from the upper part of the Proto

Canyon member in the Sonoita Creek area showing clinoptilolite in pore space...........14

13. Massive, cliff-forming volcaniclastic sandstone and conglomeratic sandstone in

the basal part of the Nogales Wash member in Grand Avenue area, south of

Mariposa Road............................................................................................................................14

14. Conglomeratic sandstone (with mudcracks) in the middle part of the Nogales Wash

member.........................................................................................................................................15

15. Thin section of conglomeratic sandstone from the middle part of the Nogales Wash

member showing mostly quartz and plagioclase framework grains in a clay and silt

matrix ............................................................................................................................................15

16. Alternating thin- to thick-bedded sandstone and conglomeratic sandstone of the

Nogales Wash member south of Mariposa Road and west of Grand Avenue.................16

17. Massive clay unit in the Mariposa member between Interstate 19 and Grand

Avenue, south of Mariposa Road.............................................................................................16

18. Sandstone in Mariposa member east of the Santa Cruz River and south of 

Sonoita Creek ..............................................................................................................................17

19. Scanning electron microscope image of sandstone from the Mariposa member..........17

20. Fine-grained facies of the Mariposa member, south of Sonoita Creek, east of the

Santa Cruz River, and near the Mount Benedict fault, consisting of alternating beds

of fine-grained volcaniclastic sandstone, siltstone, and claystone...................................18

21. Thin section of sandstone from the Mariposa member, south of Sonoita Creek, east

of the Santa Cruz River, and near the Mount Benedict fault, showing a

predominantly silt and clay matrix...........................................................................................18

22. Thin sandstone bed in Mariposa member..............................................................................18

23. Fractures in volcaniclastic sandstone and conglomerate of the Mariposa member

north of Mariposa Road and west of Interstate 19 ...............................................................19

24. North-to-northeast view of intersecting fractures in volcaniclasitc sandstone of the

Nogales Formation in the Agua Fria Canyon area ................................................................19

25. Aerial view of highly fractured outcrop in ash fall tuff unit in the lower part of the

Nogales Formation in the Peña Blanca Lake 7.5’ quadrangle ............................................19

26. Aerial view of simplified fracture map of the Nogales Wash member of the Nogales

Formation northeast of where State Highway 82 joins Grand Avenue..............................20

27. Aerial view of simplified fracture map of the Proto Canyon member of the Nogales

Formation in the Sonoita Creek area.......................................................................................21

Appendix Figure

2–1. Plots of bulk density, effective porosity, and saturated hydraulic conductivity (SHC)

for the Nogales Formation, by member...................................................................................28
v

Tables

1. Description of all samples from the Nogales Formation analyzed in this study ................9

2. Total and effective porosity and bulk density for sandstone samples from the

Nogales Formation .......................................................................................................................9

3. Saturated hydraulic conductivity for sandstone samples from the Nogales 

Formation .....................................................................................................................................10

Conversion Factors

U.S. customary units to International System of Units

Multiply By To obtain

Length

foot (ft) 30.48 centimeter (cm)

International System of Units to U.S. customary units

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

meter (m) 3.281 foot (ft) 

meter (m) 1.094 yard (yd)

kilometer (km) 0.6214 mile (mi)

Density

gram per cubic centimeter (g/cm3) 62.4220 pound per cubic foot (lb/ft3)

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as °F = (1.8 × 

°C) + 32.

Abbreviations

SEM scanning electron microscope

SHC saturated hydraulic conductivity

XRD x-ray diffraction

cm/d centimeter per day

cm/s centimeter per second

ft/d foot per day

g/cm3 gram per cubic centimeter

km kilometer

m meter

Ma mega-annum (million years ago)

μm micrometer

Hydrogeologic Investigations of the Miocene Nogales 

Formation in the Nogales Area, Upper Santa Cruz Basin, 

Arizona

By William R. Page, Floyd Gray, Mark W. Bultman, and Christopher M. Menges

Abstract

Hydrogeologic investigations were conducted to evaluate the 

groundwater resource potential for the Miocene Nogales Formation in the Nogales area, southern Arizona. Results indicate that 

parts of the formation may provide new, deeper sources of groundwater for the area. Geologic mapping determined the hydrogeologic framework of the formation by defining lithologic, mineralogic, and stratigraphic characteristics; identifying potential aquifers 

and confining units; and mapping faults and fractures which likely 

influence groundwater flow. Geophysical modeling was used to 

determine the basin geometry and thickness of the Nogales Formation and younger alluvial aquifers and to identify target areas (deep 

subbasins) which may prove to be productive aquifers.

Volcaniclastic sandstone samples from the formation 

were analyzed for porosity, bulk density, saturated hydraulic 

conductivity, and fabric. Effective porosity ranges from 16 

to 42 percent, bulk density from 1.6 to 2.47 grams per cubic 

centimeter, and saturated hydraulic conductivity (SHC) from 4 

to 57 centimeters per day (4.9×10-5 to 6.7×10-4 centimeters per 

second). Thin sections show that sandstone framework grains 

consist of quartz, feldspar, biotite, hornblende, pumice, volcanic glass, and opaque minerals. The matrix in most samples 

consists of pumice fragments, and some contain predominantly 

silt and clay. Samples with a mostly silt and clay matrix have 

lower porosity and SHC compared to samples with mostly 

pumice, which have higher and wider ranges of porosity and 

SHC. Pore space in the Nogales Formation sediments includes 

moldic, intercrystalline, and fracture porosity. Some intercrystalline pore space is partially filled with calcite cement. About 

one third of the samples contain fractures, which correspond to 

fractures noted in outcrops in all members of the formation.

Scanning electron microscope (SEM) and x-ray diffraction 

(XRD) analyses indicate that most of the samples contained 

the zeolite clinoptilolite and mixed-layer clay. X-ray diffraction 

analyses verified clinoptilolite as the only zeolite in Nogales 

Formation samples; they also verified the presence of smectite and illite clay and some kaolinite. Samples which contain 

greater amounts of clinoptilolite and lesser amounts of smectite 

have high porosity and SHC in narrow ranges. However, samples with abundant smectite and lesser amounts of clinoptilolite 

span the entire ranges of porosity and SHC for the formation. 

All members of the Nogales Formation are fractured and 

faulted as a result of Tertiary Basin and Range extensional 

deformation, which was broadly contemporaneous with deposition of the formation. These structures may have significant 

influence on groundwater flow in the upper Santa Cruz basin 

because, although many of the sediments in the formation have characteristics indicating they may be productive 

aquifers based only on porous-media flow, fracturing in these 

sediments may further enhance permeability and groundwater 

flow in these basin-fill aquifers by orders of magnitude. 

Introduction

Rapid population growth and declining annual recharge 

to alluvial basin aquifers in the Nogales, Arizona, area has 

increased the demand for additional groundwater resources 

in the upper Santa Cruz basin (fig. 1). The geology and water 

resource potential of the Nogales Formation in the upper 

Santa Cruz basin has been poorly understood because limited 

geologic and hydrogeologic data have been collected from the 

formation (Erwin, 2007; Nelson, 2007); subsequently, the formation in the basin has not been widely developed for groundwater. Clear Creek Associates (2011) completed hydrogeologic 

investigations of the Santa Cruz River microbasins area for 

the City of Nogales, Ariz., to better understand the alluvial 

aquifers of this part of the basin, as many production wells 

for the city are in this area. Their studies included the collection of new controlled source audio-frequency magnetotelluric 

(CSMAT) data; drilling and logging of several exploratory 

boreholes; and the review of existing data, maps, and well data. 

The report concluded that the water produced by some of the 

wells may have been from the Nogales Formation, rather than 

from younger or older alluvial aquifers as previously reported, 

and that parts of the formation in the area may contain productive aquifers. Our new investigations also indicate that parts 

of the Miocene Nogales Formation may contain productive 

aquifers—new, deeper sources of groundwater for the Nogales, 

Ariz., area (Gray and others, 2014). Results of our studies are 

based primarily on detailed geologic mapping and geophysical 

interpretations of the formation in the Rio Rico and Nogales 

(Ariz.) 7.5’ quadrangles (figs. 1, 2) (Page and others, 2016).
2 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Figure 1. Map of the upper Santa Cruz basin area, showing major physiographic, geologic, and hydrologic 

features in the region. Inset map in upper right shows the boundary of the upper Santa Cruz River basin 

(dashed line) in relation to the Santa Cruz River and the Rio Rico and Nogales (Arizona) 7.5’ quadrangles (red).

Tubac

Patagonia

Nogales

Kino Springs

NOGALES KINO SPRINGS

PEÑA BLANCA LAKE RIO RICO CUMERO CANYON

Atascosa 

Mountains

Tumacacori Mountains

Pajarito Mountains

Agua Fria Canyon

Peña Blanca

Canyon

Josephine Canyon

Grosvenor

Hills

Sierrita Mountains

Sonoita

Creek

31°45’

31°30’

111°00’ 110°45’

Patagonia

Mountains

Santa Cruz River

Nogales 

Wash

Amado

Tucson

Basin

Santa Rita Mountains

San Cayetano

Mountains

Cottonwood Canyon

Santa Cruz River

UNITED S

MEXICO

TATES

Sopori Wash

19

19

289

82

0123 4

0123 4

5 MILES

5 KILOMETERS

Rio Rico

Walker Canyon

Base from U.S. Geological Survey digital data, 1:24,000, 2004

Universal Transverse Mercator projection, zone 12

North American Datum 83 (NAD 83)

Modified from Page and others, 2016

Late Miocene–Holocene alluvium

EXPLANATION

Miocene Nogales Fromation

Bedrock

U.S. Geological Survey 7.5

 quadrangle boundary

 and name

NOGALES

PIMA COUNTY

SANTA CRUZ COUNTY

Patagonia

Santa Cruz River basin

Rio Rico

Nogales

Tubac

Amado

UNITED

STATES

MEXICO

SONORA

ARIZONA

Rio Rico

Quadrangle

Nogales Quadrangle

Santa Cruz River
Introduction 3

Figure 2. Map of the Rio Rico and Nogales (Arizona) 7.5’ quadrangles, showing major 

physiographic, geologic, and hydrologic features in the study area. 

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_02.ai

Late Miocene–Holocene alluvium

EXPLANATION

Miocene Nogales Fromation

Bedrock

U.S. Geological Survey 7.5

 quadrangle boundary

 and name

Normal fault—Ball and bar on

 downthrown block

NOGALES

111°00’

31°30’

31°22’30”

110°52’30”

NOGALES

RIO RICO

Rio Rico

UNITED STATES

MEXICO

Mount Benedict

19

Sonoita Creek

Nogales Wash

RIO RICO FAULT

SAN

CAYETANO FAULT

GOLD HILL FAULT

GRAND AVENUE FAULT

PROTO CA

NYON FAULT

YERBA BUENA CANYON FAULT

MOUNT BENEDICT FAULT

Rio Rico

Basin

Guevavi

Canyon

Grosvenor Hills Fresno Canyon

San Cayetano

Mountains

M o u n t

Potrero Canyon

Ephraim

Nogales

MA

RIPOSA ROAD

Canyon

Yerba Buena Canyon

GRAND

AVENUE

Mariposa Canyon

Santa Cruz River

0 0.5 1

0 0.5 1

1.5 MILES

1.5 KILOMETERS

19

82

189

Proto

 b l o c k

 Canyon

h o r s t

B e n e d i c t

Base from U.S. Geological Survey digital data, 1:24,000, 2004

Universal Transverse Mercator projection, zone 12

North American Datum 83 (NAD 83)

Modified from Page and others, 2016
4 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Nogales Formation Stratigraphy, 

Structure, and Basin Geometry

Stratigraphy

Page and others (2016) used detailed geologic mapping 

to significantly revise the stratigraphy of the Nogales Formation originally defined by Simons (1974). Based on mapping in 

the Rio Rico and Nogales (Ariz.) 7.5’ quadrangles (figs. 1, 2), 

they defined three informal members—(from base to top) the 

Proto Canyon, Nogales Wash, and Mariposa members—named 

for their type areas where they are found in the Nogales, Ariz., 

area. Nogales Formation sediments were deposited by streams 

and debris flows on alluvial fans flanking the upper Santa Cruz 

basin and in playas in axial parts of the basin. The Nogales 

Formation unconformably overlies bedrock confining units, 

which include the Jurassic Quartz Monzonite of Mount Benedict; Cretaceous plutonic, volcanic, and sedimentary rocks; and 

Tertiary volcanic and plutonic rocks (Page and others, 2016). 

In the Nogales urban area, the formation generally overlies 

the Jurassic Quartz Monzonite of Mount Benedict, which was 

a local source area for sediments in the formation. Most of 

the sediments in the formation contain pumice and volcanic 

glass fragments, indicating that the Grosvenor Hills Volcanics 

and equivalent Tertiary volcanic rocks in the Tumacacori and 

Atascosa Mountains (fig. 1) were a more regional source of 

sediments for the formation. Because of the different source 

terrains, clastic units in the formation commonly contain mixtures of Oligocene volcanic rocks and Jurassic monzonite.

Proto Canyon Member

Basal parts of the Proto Canyon member consist of 

distinctive debris-flow conglomerate, which grades upward 

into arkose conglomerate and sandstone. The coarse debrisflow conglomerate is well exposed near the contact with the 

Jurassic monzonite, south of Mount Benedict, where it is well 

consolidated and clast-supported. These beds grade upward 

into distinctive weakly consolidated, reddish-orange sequences 

of alternating beds of arkose conglomerate and sandstone. 

The basal debris-flow conglomerate and arkose units are well 

exposed in the basin north of Proto Canyon and State Highway 82 and south of Mount Benedict (fig. 2) (Page and others, 

2016), where their combined thickness is estimated to be about 

100 to 250 meters (m) thick.

The lower units of the Proto Canyon member above the 

basal debris-flow conglomerate and arkose units consist of 

fining-upward cyclic sequences of volcaniclastic conglomerate, sandstone, and pumice siltstone; these units form massive 

cliffs in the Proto Canyon area, primarily along and south of 

State Highway 82. Middle parts of the member contain red and 

gray sandy and gravelly claystone, pale red arkosic conglomerate and sandstone, and yellowish-gray to brown volcaniclastic sandstone and conglomeratic sandstone; these units are best 

exposed in the Yerba Buena Canyon area (fig. 2). Lower and 

middle parts of the member are mostly exposed south of Proto 

Canyon and State Highway 82, extending southward across 

the international border into Sonora, Mexico.

The upper part of the Proto Canyon member consists 

mainly of pinkish-gray to yellowish-gray, moderately consolidated volcaniclastic sandstone and conglomerate; these rocks 

are mostly exposed in the Grand Avenue area, north of Mariposa Road (Page and others, 2016). Sandstone and conglomerate in the upper part of the member contain abundant monzonite clasts, reflecting localized erosion of the Quartz Monzonite 

of Mount Benedict. The thickness of the Proto Canyon member 

is highly variable, but maximum thickness is about 450 m.

The Proto Canyon member is also exposed in the Sonoita 

Creek area, where it laps onto the Grosvenor Hills Volcanics 

in the southern Grosvenor Hills. In this area, the lower part of 

the unit is pinkish-gray, cliff-forming to ledgy volcaniclastic 

conglomerate containing clasts and grains of mostly white 

and red porphyritic volcanic rocks, brownish-gray rhyodacite, 

pumice, and latite derived from the Grosvenor Hills Volcanics. 

The upper part of the unit is fine-grained, moderately sorted 

volcaniclastic sandstone and some conglomeratic sandstone, 

which weathers to distinctive rounded ledges. These rocks are 

moderately fractured in the Sonoita Creek area.

Nogales Wash Member

The Nogales Wash member is only present in the Nogales 

7.5’ quadrangle (Page and others, 2016), and exposures are 

limited to south of Mariposa Road, extending from Ephraim 

Canyon to about 4 kilometers (km) east of Grand Avenue 

(fig. 2). Distribution of the member, combined with on-lapping 

relations with the lower part of the Proto Canyon member, 

suggests the Nogales Wash member sediments were deposited 

in a paleovalley eroded into the Proto Canyon member, coincident with the modern-day Nogales Wash (Page and others, 

2016). The Nogales Wash member is estimated to be as much 

as 150 m thick in the deeper subbasins of the upper Santa Cruz 

basin (Page and others, 2016). The basal 20–30 m contains 

distinctive massive cliffs of yellowish-gray to pinkish-gray, 

moderately consolidated volcaniclastic sandstone and conglomeratic sandstone, and most of the other parts of the 

member contain alternating beds of thin- to thick-bedded 

volcaniclastic sandstone and conglomeratic sandstone. Rocks 

of the Nogales Wash member are pervasively fractured in the 

upper Santa Cruz basin.

Mariposa Member

The Mariposa member is exposed in the Mariposa Road 

and Interstate 19 areas, where it contains alternating beds of 

conglomerate, conglomeratic sandstone, sandstone, siltstone, 

and claystone; the member is generally less consolidated 

and more calcareous compared to the other members. In the 

Mariposa Road area, a 60-m-thick massive claystone unit 

represents playa deposits in axial parts of the basin (Page and 

others, 2016). The claystone may be a significant confining 
Nogales Formation Stratigraphy, Structure, and Basin Geometry 5

unit in the basin, but more subsurface data need to be collected 

to determine its lateral continuity and thickness. The member 

is widely exposed in the basin south of Sonoita Creek, east of 

the Santa Cruz River, and north of Guevavi Canyon, where it 

contains pinkish-gray alternating beds of sandstone, siltstone, 

and claystone, like in the Mariposa Road area. These units, 

however, are generally thinner bedded and finer grained. The 

Mariposa member is also exposed southeast of State Highway 

82 and just north of the international border, where lower 

parts of the member consist of conglomeratic sandstone, finegrained sandstone, and thin, discontinuous lava flows 3–5 m 

thick. One basalt sample was dated and yielded a 40Ar/39Ar 

(argon-argon) age of 11.67±0.09 mega-annum (Ma) (Cosca 

and others, 2013; Page and others, 2016); this date provides an 

absolute minimum age for the Nogales Formation.

Structure

Structural features in the Nogales, Ariz., area primarily 

formed during early to late Miocene extensional deformation, 

which occurred in southern Arizona mostly from 20 to 10 

Ma (Menges, 1981; Menges and McFadden, 1981; Menges 

and Pearthree, 1989). Extensional deformation was broadly 

contemporaneous with deposition of the Nogales Formation, 

based on observations that all members of the formation are 

faulted and exhibit abundant intra-formational faults and 

fractures and moderately to steeply inclined bedding dips. 

Extensional faulting in the area lasted until late Miocene time, 

based on the observation that faults only cut the very oldest 

late Miocene basin-fill deposits (postdating Nogales Formation deposition) and that deposits from the Pliocene through 

the Holocene are undeformed (Page and others, 2016).

The main structural feature in the study area is the Mount 

Benedict horst block (fig. 2) (Page and others, 2016), a triangular zone of uplifted Quartz Monzonite of Mount Benedict 

(Jurassic) and overlying members of the Nogales Formation. 

The fault bounding the east side of the horst block is the 

Mount Benedict fault, the major fault in the region which controls the location of the course of the Santa Cruz River from 

the Rio Rico area southward into Mexico. The fault is exposed 

northwest of Guevavi Canyon and southeast of Sonoita Creek 

(Page and others, 2016), where it dips northeast and offsets 

rocks of the Jurassic monzonite and overlying Salero Formation in the footwall, against the Mariposa member of the 

Nogales Formation in the hanging wall. Other known exposures of the fault are in the Cumero Canyon 7.5’ quadrangle 

(fig. 1), southeast of the intersection of State Highway 82 and 

the Santa Cruz River. At this location, the fault juxtaposes 

clayey arkosic conglomerate of the Proto Canyon member in 

the footwall, against volcaniclastic sandstone of the Mariposa 

member in the hanging wall.

The Grand Avenue fault (fig. 2) forms the west margin 

of the Mount Benedict horst block. The fault is exposed just 

south of Mariposa Road and west of Grand Avenue, where it 

strikes northeast and dips northwest. The southern part of the 

fault juxtaposes rocks of the Nogales Wash member against 

those of the Mariposa member of the Nogales Formation, but 

north of Mariposa Road, rocks of the Mariposa member are 

faulted against those of the Proto Canyon member and the 

Quartz Monzonite of Mount Benedict. Several other concealed 

faults interpreted from airborne transient electromagnetic data 

and other geophysical data are mapped west of the Grand Avenue fault (Page and others, 2016); these faults and the Grand 

Avenue fault form a complex graben system in the subsurface 

west of the horst block (fig.2).

Basin Geometry

Basin Evolution

Geophysical data were interpreted to determine basin 

geometry and thickness of the Nogales Formation and younger 

alluvial aquifers and to identify target areas (deep subbasins) 

which may prove to be productive aquifers. The upper Santa 

Cruz depositional basin includes the area west of the Patagonia Mountains, south of the Grosvenor Hills, west of the San 

Cayetano and Santa Rita Mountains, and east of the Atascosa 

and Tumacacori Mountains (fig. 1) and extends southward 

into Sonora, Mexico. The basin geometry is complex because 

of a highly irregular erosion surface that predates the Nogales 

Formation and developed on Jurassic and Cretaceous rocks 

(Page and others, 2016), which were deformed by episodes 

of Miocene Basin and Range extension and older pre-Tertiary 

deformational events, most notably Cretaceous plutonism and 

faulting related to the Laramide orogeny (Simons, 1974).

Sediments of the Proto Canyon member of the Nogales 

Formation represent initial deposition in the southern part of 

the upper Santa Cruz basin and were laid down across an area 

coincident with that of the modern day basin. During deposition of the Proto Canyon member, Mount Benedict (fig. 2) was 

likely a paleotopographic high near the center of the basin, 

based on coarse debris-flow conglomerate at the base of the 

Proto Canyon member shed off the flanks of Mount Benedict. 

The horst block experienced multiple stages of uplift during 

deposition of the Nogales Formation based on unconformities bounding each member of the formation and onlapping 

relations between the Proto Canyon member and the Nogales 

Wash and Mariposa members (Page and others, 2016).

Uplift of the Mount Benedict horst block occurred during 

and (or) following deposition of the Proto Canyon member to 

expose the basal debris-flow conglomerate and to further compartmentalize the southern part of the upper Santa Cruz basin 

into two main basins: one west of the horst block and east of the 

Atascosa and Tumacacori Mountains, and another east of the 

horst block and Santa Cruz River, south of the Grosvenor Hills, 

and west of the Patagonia Mountains (figs. 1, 2). Further faulting 

and uplift of the horst block continued throughout and following 

deposition of the Nogales Formation, based on the observation 

that all members are fractured and faulted, that major faults cut 

the very oldest part of alluvial basin-fill deposits that postdate the 

Nogales Formation and overlie it, and that sediments from the 

Pliocene through the Holocene are generally undeformed.
6 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Depth to Bedrock Maps

Based on geophysical interpretations, we constructed 

depth to bedrock maps to delineate subsurface contacts and 

fault boundaries between Jurassic and Cretaceous bedrock confining units and the overlying Nogales Formation. The maps 

also define the geometry of deep subbasins (fig. 3) that contain 

aquifers of the Nogales Formation and overlying younger 

basin fill and alluvium. The subbasins are about 500 to 800 m 

deep and contain thick sections of fractured Nogales Formation sediments; they are considered target areas for additional 

groundwater resources in the upper Santa Cruz basin.

Gettings and Houser (1997) used complete Bouguer 

gravity anomaly data to obtain a preliminary depth to bedrock for the Santa Cruz basin. We used the 1996 Patagonia 

aeromagnetic survey (Sweeney and Hill, 2001) to produce 

a depth to bedrock map with a higher spatial resolution than 

preliminary maps in the Rio Rico and Nogales (Ariz.) 7.5’ 

quadrangles. Analysis of the aeromagnetic data included three 

methods to estimate depth to bedrock: Euler deconvolution, 

horizontal gradient magnitude, and analytic signal. The final 

depth to bedrock map was produced by choosing the maximum depth from each of the three methods at a given location 

and combining all maximum depths. The resulting map (fig. 3) 

provides a much more detailed description of depth to bedrock 

in the upper Santa Cruz basin study area than had previously 

existed and shows the location and geometry of the six deep 

subbasins (fig. 3).

Results of Porosity, Bulk Density, 

Saturated Hydraulic Conductivity, 

and Fabric Analyses for the Nogales 

Formation

A total of 22 sandstone samples were taken from the 

Nogales Formation for analysis (fig. 4, table 1). Of those 

samples, 14 samples were analyzed for total and effective 

porosity and bulk density (table 2), and 13 samples were analyzed for saturated hydraulic conductivity (SHC) (table 3). For 

fabric analyses, thin sections were examined for 21 samples 

(appendix 1), and 5 samples were investigated using scanning 

electron microscope (SEM) and x-ray diffraction (XRD) methods. Table 1 lists all samples analyzed and identifies the location, formation member, and type or types of analyses reported 

for each, as well as any associated figures. All samples were 

collected from outcrops, and all samples are sandstone. The 

values obtained, therefore, are not representative of the full 

spectrum of lithostratigraphic units in the Nogales Formation, 

although sandstone is the most abundant rock type in the formation. Our analyses were limited to sandstones because other 

units in the formation, including clay-rich units in the Mariposa and Proto Canyon members, were typically too weakly 

consolidated for porosity and SHC analyses. While both 

total and effective porosity was measured, effective porosity 

(the amount of mutually interconnected pore space) is key 

to hydrologic investigations, so all porosity values discussed 

henceforth represent only effective porosity.

Effective porosity values from the Nogales Formation 

range from 16 to 42 percent (table 2). The highest porosity 

was from sandstone in the upper part of the Proto Canyon 

member (fig. 2–1B), and the lowest from sandstone in the 

lower part of the Mariposa member (fig. 2–1F). Gettings and 

Houser (1997) calculated a porosity of 16 percent for rocks 

equivalent to the Nogales Formation, based on a combination 

of downhole gravimeter data, grain density measurements of 

cuttings, and surface gravimetric profiles. Their porosity value 

is low compared to most of the results from our analyses.

Bulk density in the formation ranges from 1.60 grams per 

cubic centimeter (g/cm3) to as much as 2.47 g/cm3 (table 2); 

the highest value is from moderately consolidated sandstone 

near the base of the Nogales Wash member (fig. 2–1A), and 

the lowest is from sandstone in the lower part of the Mariposa 

member (fig. 2–1A). Gettings and Houser (1997) calculated 

saturated bulk density for rocks equivalent to the Nogales Formation, based on downhole gravimetric measurements; they 

reported values from 2.00 to 2.38 g/cm3, which are in agreement with most of the values determined by our analyses. 

Values for SHC for the formation are wide ranging, from 

4 to 57 centimeters per day (cm/d) (table 3). Both the highest 

and lowest SHC are from the upper part of the Proto Canyon 

member (fig. 2–1C). Published SHC data for the Nogales Formation are sparse, but Erwin (2007) reported composite values 

of 0.4 and 0.5 feet per day (ft/d) (12 and 15 cm/d) from aquifer 

tests completed in wells penetrating alluvium that postdates the 

Nogales Formation and in the Nogales Formation in the Kino 

Springs area (fig. 1). Nelson (2007) reported hydraulic conductivities for the Nogales Formation in the upper Santa Cruz 

basin at 0.17 ft/d (5.1 cm/d), 0.3 ft/d (9.1 cm/d), and 0.43 ft/d 

(13.1 cm/d), based on aquifer tests west of Tubac, Ariz. (fig. 1).

Fabric analyses included petrographic, SEM, and XRD 

methods. Twenty-one thin sections from all members of the 

Nogales Formation were examined and described (appendix 1). 

Thin sections show that framework grains generally consist 

of quartz, feldspar, biotite, hornblende, porphyritic volcanic 

clasts with biotite and hornblende, quartz-biotite monzonite 

porphyritic clasts, pumice and altered volcanic glass, small 

scattered opaque minerals including ilmenite, iron oxide, and 

manganese oxide. Approximately half of the thin sections have 

a matrix of mostly pumice and glass, and half contain combinations of pumice, glass, silt, and clay (appendix 1). Samples 

with a predominantly silt and clay matrix generally have lower 

porosity and SHC (porosities at 26 percent and lower; SHC 

15–33.4 cm/d; tables 2, 3) compared to samples with a mostly 

pumice and glass matrix, which have higher porosity and SHC 

as well as wider ranges of porosity (20–42 percent; table 2) and 

SHC (5.6–57 cm/d; table 3).

Most sandstone in the formation is poorly sorted, but 

some is moderately sorted and fine grained. Only two such 

samples were analyzed, and both have low porosity values 
Results of Porosity, Bulk Density, Saturated Hydraulic Conductivity, and Fabric Analyses for the Nogales Formation 7

Figure 3. Depth to bedrock in the Rio Rico and Nogales (Arizona) 7.5’ quadrangles (study area shown in figure 2). Deeper 

subbasins in the area are numbered: (1) Grand Avenue subbasin, (2) Sonoita Creek West subbasin, (3) Sonoita Creek East 

subbasin, (4) Highway 82 subbasin, (5) Potrero Canyon subbasin, and (6) West Nogales subbasin. Black areas indicate 

bedrock outcrops.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_03.ai 3480000 3475000 3470000

505000 510000

633.2

510.5

443.9

409.1

378.8

352.5

329.7

307.9

290.1

270.7

250.1

230.7

211.2

191.5

171.7

152.2

133.2

112.8

74.8

0 1 2 MILES

0 1 2 KILOMETERS

NAD27 / UTM ZONE 12N

Bedrock

outcrop

Depth to bedrock—Depth

 in meters

Subbasin identifier

Grand Avenue

Sonoita Creek West

Sonoita Creek East

Highway 82

Potrero Canyon

West Nogales

EXPLANATION

N
8 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Figure 4. Locations of Nogales Formation samples analyzed in this study. Sample site 

identifiers correspond to entries in tables 1–3.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_04.ai

Late Miocene–Holocene alluvium

EXPLANATION

Miocene Nogales Fromation

Bedrock

U.S. Geological Survey 7.5

 quadrangle boundary

 and name

Location of fracture outcrop with

 figure identifier.

Figure 27

NOGALES

Sample site and table idenitifer

Mariposa member

Nogales Wash member

Proto Canyon member

500000 505000 510000

3470000 3475000 3480000 3485000

111°00’

31°30’

31°22’30”

110°52’30”

NOGALES

RIO RICO

Rio Rico

UNITED STATES

MEXICO

Mount Benedict

Sonoita Creek

Rio Rico

Basin

Guevavi

Canyon

Grosvenor Hills Fresno Canyon

San Cayetano

Mountains

M o u n t

Potrero Canyon

Ephraim

Nogales

MA

RIPOSA ROAD

Canyon

Yerba Buena Canyon

GRAND

AVENUE

Mariposa Canyon

Santa Cruz River

0 0.5 1

0 0.5 1

1.5 MILES

1.5 KILOMETERS

19

19

82 Proto

 b l o c k

 Canyon

h o r s t

B e n e d i c t

Base from U.S. Geological Survey digital data, 1:24,000, 2004

Universal Transverse Mercator projection, zone 12

North American Datum 83 (NAD 83)

Modified from Page and others, 2016

Figure 27

Figure 26

Nogales Wash

189

18

17

3 3

4

7

6

15, 16

19 11 13

12

5

21

20

10

22

14

1

8

9

2
Results of Porosity, Bulk Density, Saturated Hydraulic Conductivity, and Fabric Analyses for the Nogales Formation 9

Table 1. Description of all samples from the Nogales Formation analyzed in this study.

[Columns include (from left to right) (1) sample site identifiers keyed to figure 4, (2) original field sample number, (3) Universal Transverse Mercator 

(UTM) easting and northing, (4) Nogales Formation member name, (5) types of analyses performed, and (6) associated figure (outcrop photograph, thin 

section, or SEM image). SHC, saturated hydraulic conductivity; phys. prop., total and effective porosity and bulk density; TS, thin section; SEM, scanning electron microscope; XRD, x-ray diffraction]

Sample 

site

Sample 

number

UTM Zone 12 Nogales Formation 

member Analyses Figure 

Easting Northing number

1 10-RP-2 505843 3469986 Mariposa SHC, phys. prop., TS, SEM, XRD 22

2 10-RP-9 506150 3470251 Mariposa TS

3 RP-12-9 506324 3481500 Mariposa TS

4 RP-12-11 504162 3479807 Mariposa phys. prop., TS 20, 21

5 RP-12-19a 508873 3467513 Mariposa SHC, phys. prop., TS

6 RP-12-27 506276 3478109 Mariposa SHC, phys. prop., TS, SEM, XRD 18, 19

7 RP-12-29 505905 3479060 Mariposa TS

8 10-RP-4 506567 3469545 Nogales Wash SHC, TS 16

9 10-RP-10 506142 3467200 Nogales Wash phys. prop., TS 13

10 RP-12-15 509934 3466664 Nogales Wash SHC, TS

11 RP-12-16 508250 3466814 Nogales Wash TS

12 RP-12-24 504837 3466727 Nogales Wash phys. prop., TS

13 RP-12-46 505543 3466868 Nogales Wash SHC, phys. prop., TS 14, 15

14 10-RP-3 505568 3470775 Proto Canyon SHC, phys. prop., TS, SEM, XRD 9, 10

15 RP-12-4a 505796 3471725 Proto Canyon SHC, phys. prop., TS

16 RP-12-4b 505796 3471725 Proto Canyon SHC

17 RP-12-7 505388 3482056 Proto Canyon SHC, phys. prop., TS, SEM, XRD 11, 12

18 RP-12-8 505632 3483117 Proto Canyon TS

19 RP-12-14 506579 3466697 Proto Canyon phys. prop., TS

20 RP-12-21 509952 3470259 Proto Canyon SHC, phys. prop., TS, SEM, XRD 5, 6, 7

21 RP-12-32 509441 3468542 Proto Canyon SHC, phys. prop., TS

22 RP-12-42a 511913 3471111 Proto Canyon SHC, phys. prop., TS

Table 2. Total and effective porosity and bulk density for sandstone samples 

from the Nogales Formation.

[Analyses performed at the U.S. Geological Survey Hydrologic Research Laboratory in 

Sacramento, California. Sample sites are shown in figure 4. %, percent; g/cm3, grams per 

cubic centimeters]

Sample 

site

Sample 

number

Nogales Formation 

member

Total 

porosity 

(%)

Effective 

porosity 

(%)

Bulk density 

(g/cm3)

1 10-RP-2 Mariposa 29 24 1.6 

4 RP-12-11 Mariposa 23 16 2.07

5 RP-12-19a Mariposa 25 21 2.23

6 RP-12-27 Mariposa 42 36 2.37

9 10-RP-10 Nogales Wash 37 31 2.47

12 RP-12-24 Nogales Wash 28 22 1.86

13 RP-12-46 Nogales Wash 25 22 1.76

14 10-RP-3 Proto Canyon 49 42 2.0

15 RP-12-4a Proto Canyon 35 26 2.41

17 RP-12-7 Proto Canyon 26 22 1.94

19 RP-12-14 Proto Canyon 23 20 2.13

20 RP-12-21 Proto Canyon 39 32 2.2

21 RP-12-32 Proto Canyon 34 29 1.78

22 RP-12-42a Proto Canyon 31 24 1.79
10 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

compared to other samples and wide-ranging SHC, from 5.6 

to 57 cm/d. About 6 samples from the formation contained 

fractures, and all were open fractures. Samples with fractures 

have wide-ranging porosity (26–42 percent) and low SHC 

(4–15 cm/d). Fractured sandstones also have higher bulk 

densities compared to other samples, ranging from 2.0 to 

2.47 g/cm3. Most samples from the Mariposa member contain 

secondary calcite cement, which partially fills intercrystalline 

pore space. Samples with calcite cement have wide-ranging 

porosity (16–36 percent) and SHC (15–33.4 cm/d).

Five samples from the Nogales Formation were analyzed 

using SEM and XRD methods to identify and describe clay 

composition in the formation. Analyses indicate that most 

of the samples contain the zeolite clinoptilolite and varying 

amounts of mixed-layer clay. X-ray diffraction analyses verified clinoptilolite as the only zeolite in Nogales Formation 

samples as well as the presence of mixed-layer smectite and 

illite clay and some kaolinite. Clinoptilolite likely precipitated 

in pore space of the Nogales Formation sediments during postdepositional basin diagenesis, similar to processes of sedimentary basin diagenesis described by Gotardi and Galli (1985), 

whereby clinoptilolite is precipitated from the dissolution of 

silica-rich volcanic glass as it reacts with alkaline meteoric 

groundwater. In most samples, clinoptilolite crystals occur as 

disseminated microcrystalline aggregates, filling intercrystalline pore space. The presence of clinoptilolite, in addition to 

mixed-layer smectite and illite clays, partly accounts for the 

moderately high porosity in the formation, which ranges from 

16 to as much as 42 percent. Iijima (2001) reported similar 

porosity values of 20 to 40 percent for clinoptilolite-bearing 

Cenozoic to Mesozoic basinal volcaniclastic sandstones in 

Japan, and these rocks form the major commercial petroleum 

reservoirs in those basins. Scanning electron microscope 

and x-ray diffraction methods show that samples with 

greater clinoptilolite and lesser smectite have high porosity (32–36 percent) and SHC (32.7–35.3 cm/d) in narrow 

ranges. Conversely, samples with abundant smectite and minor 

clinoptilolite have wide-ranging porosity, with values ranging 

from a low of 24 percent to the maximum value for the entire 

formation at 42 percent, and values for SHC that range from 

the lowest for the formation at 4 cm/d to the maximum for the 

formation at 57 cm/d. 

Discussion of Analyses by Nogales 

Formation Member

Proto Canyon Member

The Proto Canyon member of the Nogales Formation is 

lithologically diverse compared to the other members and, in 

turn, has wide-ranging values for porosity, bulk density, and 

SHC. The highest porosity is from sandstone in the upper 

part of the member, and the lowest from the middle part 

(fig. 2–1B). The highest SHC is also from sandstone in the 

upper part of the member, and the lowest from the middle and 

upper parts (fig. 2–1C). The highest bulk density (fig. 2–1A) is 

from moderately consolidated sandstone in the upper part of 

the member (2.41 gm/cm3), and the lowest densities (1.78 and 

1.79 g/cm3) from samples in the middle part, which contains 

more claystone than other parts of the member.

The lower part of the member (above the basal conglomerate and arkose) contains fining-upward cyclic sequences 

of conglomerate, sandstone, and laminated pumice siltstone 

(fig. 5). Sandstone from these sequences (sample RP-12-21) 

Table 3. Saturated hydraulic conductivity for sandstone samples from the Nogales 

Formation.

[Analyses performed at the U.S. Geological Survey Hydrologic Research Laboratory in Sacramento, 

California. Sample sites are shown in figure 4. cm/s, centimeters per second; cm/d, centimeters per day]

Sample 

site

Sample 

number

Nogales Formation 

member

Saturated hydraulic conductivity

(cm/s) (cm/d)

1 10-RP-2 Mariposa 3.9×10−4 33.4

5 RP-12-19a Mariposa 6.4×10−5 5.6

6 RP-12-27 Mariposa 3.8×10−4 32.7

8 10-RP-4 Nogales Wash 4.3×10−4 38

10 RP-12-15 Nogales Wash 3×10−4 26

13 RP-12-46 Nogales Wash 2.7×10−4 23.6

14 10-RP-3 Proto Canyon 4.9×10−5 4.0

15 RP-12-4a Proto Canyon 1.7×10−4 15

16 RP-12-4b Proto Canyon 5.0×10−4 43

17 RP-12-7 Proto Canyon 6.7×10−4 57

20 RP-12-21 Proto Canyon 4.1×10−4 35.3

21 RP-12-32 Proto Canyon 5.7×10−5 4.9

22 RP-12-42a Proto Canyon 1.7×10−4 14.3 
Discussion of Analyses by Nogales Formation Member 11

has relatively high porosity at 32 percent, bulk density at 

2.2 g/cm3, and SHC at 35.3 cm/d. Thin sections show a mostly 

pumice matrix with moderate amounts of open pore space 

(fig. 6). Scanning electron microscope and x-ray diffraction 

analyses for this sample indicated high amounts of clinoptilolite (fig. 7) and minor smectite.

Middle parts of the member, which are exposed primarily 

south of Proto Canyon and State Highway 82 and extending 

to the international border (fig. 2), contain alternating arkosic 

conglomerate, gravelly claystone, and sandstone beds (fig. 8). 

The middle part of the member is less fractured than the other 

parts, probably because of higher amounts of clay. Sandstones 

from the middle part of the member (samples RP-12-14, RP12-42a, and RP-12-32) have low to intermediate porosity of 

20, 24, and 29 percent, respectively. Bulk density is low for 

samples RP-12-32 (1.78 g/cm3) and RP-12-42a (1.79 g/cm3) 

and intermediate for sample RP-12-14 (2.13 g/cm3). The 

lowest porosity in the middle part is from sandstone that is 

interbedded with sandy claystone and siltstone beds (sample 

RP-12-14), and thin sections show moderate moldic pore 

space within pumice grains, minor intercrystalline pore space, 

and a combination pumice, silt, and clay matrix. Samples 

RP-12-32 and RP-12-42a, in addition to having low to 

intermediate porosity, also have low SHC at 4.9 cm/d and 

14.3 cm/d, respectively. Similar to sample RP-12-14 above, 

both samples have a combination pumice, silt, and clay matrix 

and moderate moldic and minor intercrystalline pore space. 

Figure 5. Cyclic fining-upward sequences in the lower part 

of the Proto Canyon member in Proto Canyon. Cycles generally 

consist of volcaniclastic conglomerate (vc) and conglomeratic 

sandstone (vcs) capped by white pumice siltstone (ps); these 

sequences also contain some debris-flow conglomerate (dfc). 

Sandstone from these sequences (sample RP-12-21; site 20 on 

fig. 4) has relatively high effective porosity at 32 percent and a 

saturated hydraulic conductivity value of 35.3 centimeters per 

day. Thin sections (fig. 6) show that these rocks contain moderate 

amounts of moldic and minor intercrystalline pore space.

Figure 6. Thin section of sandstone (sample RP-12-21; site 20 on fig. 4) from the lower part of 

the Proto Canyon member at Proto Canyon showing a predominantly pumice fragment matrix and 

mostly plagioclase, quartz, biotite, and hornblende framework grains. See figure 5 for photograph 

of outcrop. Plane polarized light; open pore space is in light blue (one example indicated on image). 

(mm, millimeter) 

_cmrl00_0034_sir_page\report_figures\figure_05.ai

dfc

ps

vcs

vc

ps

0.5 millimeter

P

P

H P

B

Open pore space

Q

Q

P

Plagioclase

Q Quartz

B Biotite

H Hornblende

EXPLANATION

P

P

Plagioclase

Q Quartz

B Biotite

H Hornblende

EXPLANATION
12 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Sample RP-12-32 also has abundant silt and clay layers, which 

may partly explain the low SHC value, the second lowest of 

all samples in the formation.

The upper part of the Proto Canyon member is moderately consolidated sandstone (sample 10-RP-3; fig. 9) and has 

the highest effective porosity (42 percent) of all samples from 

the entire Nogales Formation. Thin sections show abundant 

intercrystalline, moldic, and fracture pore space, as well as a 

pumice and volcanic glass fragment matrix. This rock has the 

lowest SHC of all Nogales Formation samples (4.0 cm/d) and 

contradicts the observation that many sediments with high 

porosity generally have corresponding high hydraulic conductivity (Pryor, 1973; Freeze and Cherry, 1979). X-ray diffraction analyses indicate that the rock has very high amounts 

of smectite and minor amounts of clinoptilolite. Scanning 

electron microscope analyses show abundant smectite and 

illite clay coating the surfaces of tabular-shaped clinoptilolite 

crystals, in addition to abundant interspersed fibrous, organic 

material (fig. 10). A possible explanation for the very high 

Figure 7. Scanning electron microscope image of sandstone 

(sample RP-12-21; site 20 on fig. 4) from the lower part of the 

Proto Canyon member at Proto Canyon showing clinoptilolite 

in pore space. Clinoptilolite crystals are generally less than 25 

micrometers (μm) in size. See figure 5 for photograph of outcrop. 

Image shows primarily clinoptilolite; smectite and illite clay is 

likely present, but precise identification of clay could not be 

determined from these analyses.

Figure 8. Red and light gray gravelly claystone (below black 

line) and overlying gray volcaniclastic sandstone beds (above 

black line) in the middle part of the Proto Canyon member in Yerba 

Buena Canyon. Exposed part of gray sandstone bed above black 

line at far right is about 0.5 meter thick. These rocks (samples 

RP-12-14, RP-12-42a, and RP-12-32; sites 19, 22, and 21 on fig. 4) 

have low to intermediate porosity values at 20, 24, and 29 percent 

and low saturated hydraulic conductivity values at 4.9 and 14.3 

centimeters per day.

Figure 9. Pinkish-gray volcaniclastic sandstone in the uppermost 

part of the Proto Canyon member between Interstate 19 and Grand 

Avenue, north of Mariposa Road; pick for scale. Sandstone from 

this location (sample 10-RP-3; site 14 on fig. 4) has the highest 

effective porosity for the entire Nogales Formation at 42 percent 

but also has the lowest saturated hydraulic conductivity for the 

formation at 4.0 centimeters per day.

0.5 METER
Discussion of Analyses by Nogales Formation Member 13

porosity and extremely low SHC is that clay coatings and 

organic material clog up pore space to inhibit SHC. In comparison with sample 10-RP-3, sample RP-12-21 in the lower 

part of the Proto Canyon member (fig. 5) has moderately high 

porosity (32 percent) and SHC (35.3 cm/d). Further, SEM 

and XRD analyses indicate that this rock contains abundant 

clinoptilolite and minor smectite; the clinoptilolite crystals 

appear “cleaner” (fig. 7) and lack the clay coatings and organic 

material observed in sample 10-RP-3. 

We analyzed a coarse-grained conglomeratic sandstone 

(sample RP-12-4a) and a fine-grained sandstone (sample 

RP-12-4b) from the upper part of the Proto Canyon member 

at the same location and stratigraphic horizon. The coarsegrained conglomeratic sandstone has relatively low porosity 

(26 percent) and SHC (15 cm/d), and thin sections show a 

predominantly clay and silt matrix and moderate amounts 

of secondary calcite filling intercrystalline pore space. The 

coarse-grained conglomeratic sandstone has the highest bulk 

density for the Proto Canyon member at 2.41 g/cm3, and 

Figure 10. Scanning electron microscope image of sandstone (sample 10-RP-3; site 14 on fig. 4) from the 

uppermost part of the Proto Canyon member between Interstate 19 and Grand Avenue, north of Mariposa 

Road, showing clinoptilolite in pore space. Note the abundant smectite/illite clay coating tabular 

clinoptilolite and the abundant interspersed fibrous organic material. Clinoptilolite crystals are generally 

25 micrometers (μm) or greater in size. See figure 9 for photograph of outcrop.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_10.ai

S S

S

S

S

S

S

O

O

S

S

O

S Smectite\illite

O Organic material

EXPLANATION

thin sections show abundant fracture porosity, which reflects 

greater consolidation in the sandstone of the upper part of 

the member compared to the middle and lower parts of the 

member. The fine-grained sandstone (sample RP-12-4b) has 

significantly higher SHC at 43 cm/d (the second highest SHC 

of all Nogales Formation samples), but no porosity or fabric 

data were available to interpret and explain the higher SHC.

Sample RP-12-7, from sandstone in the upper part of the 

Proto Canyon member in the Sonoita Creek area (fig. 11), has 

relatively low porosity (22 percent) but has the highest SHC 

(57 cm/d) for the entire Nogales Formation. Thin sections 

show the rock is moderately sorted and fine grained and has 

a pumice and glass matrix, moderate moldic pore space, and 

moderate to abundant amounts of micro-intercrystalline pore 

space between small, angular, disaggregated pumice and glass 

fragments. X-ray diffraction analyses indicate that the sample 

contains abundant clinoptilolite and smectite, and SEM 

analyses show moderate amounts of open pore space (fig. 12), 

which may partly explain the high SHC.

S 

S Smectite\illite

O Organic material

EXPLANATION
14 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Nogales Wash Member

The Nogales Wash member typically contains ledgy to 

cliff-forming sandstone and conglomeratic sandstone and 

generally lacks claystone beds, unlike the other formation 

members. Three samples from the member analyzed for physical properties have low to intermediate porosity at 22, 22, 

and 31 percent (samples RP-12-24, RP-12-46, and 10-RP-10, 

respectively). The highest porosity is from sandstone in the 

cliff-forming lower part of the member (fig. 2–1D); these 

rocks also have the highest bulk density for the entire formation (fig. 2–1A) and are pervasively fractured because of 

their brittleness from a higher degree of consolidation and 

lesser amounts of claystone compared to the other members. 

Saturated hydraulic conductivity for the member is intermediate and ranges from 23.6 to 38 cm/d; the highest SHC is from 

units in the middle part of the member (fig. 2–1E).

Sample 10-RP-10 has the highest porosity in the member 

(31 percent) and is from moderately consolidated sandstone in 

the lower cliff-forming part of the member (fig. 13). Thin sections show abundant fracture porosity and moderate amounts 

of moldic and intercrystalline pore space. Sample 10-RP-10 

has the highest bulk density (2.47 g/cm3) for the entire 

Figure 13. Massive, cliff-forming volcaniclastic sandstone 

and conglomeratic sandstone in the basal part of the Nogales 

Wash member in Grand Avenue area, south of Mariposa 

Road; pen in center for scale. Note the internal deformation, 

including abundant fractures, and breccia zone in the center of 

the photograph. Sandstones from the Nogales Wash member 

are moderately consolidated and brittle, have the highest bulk 

density in the formation (2.47 grams per cubic centimeter), and 

are pervasively fractured compared to other members of the 

formation. Sandstone from this location (sample 10-RP-10; site 9 

on fig. 4) has a porosity of 31 percent.

Figure 11. Fine-grained, moderately sorted volcaniclastic 

sandstone in the upper part of the Proto Canyon member in the 

Sonoita Creek area. Sandstone from this unit (sample RP-12-7; 

site 17 on fig. 4) has a low porosity at 22 percent and the highest 

saturated hydraulic conductivity for the entire Nogales Formation 

at 57 centimeters per day.

Figure 12. Scanning electron microscope image of sandstone 

(sample RP-12-7; site 17 on fig. 4) from the upper part of the Proto 

Canyon member in the Sonoita Creek area showing clinoptilolite 

in pore space. Note the moderate amounts of open pore space. 

Clinoptilolite crystals are generally less than 25 micrometers (μm) in 

size. See figure 11 for photograph of outcrop. Image shows primarily 

clinoptilolite; smectite and illite clay is likely present, but precise 

identification of clay could not be determined from these analyses. 
Discussion of Analyses by Nogales Formation Member 15

formation (table 2) and corresponds to greater consolidation 

compared to other members of the formation.

Sample RP-12-46 is from calcareous, conglomeratic 

sandstone in the middle part of the member (fig. 14). Thin 

sections show an abundant clay and silt matrix (fig. 15) with 

some moldic pore space but minimal to no intercrystalline 

pore space. This rock has a low porosity (22 percent), low bulk 

density (1.76 gm/cm3), and intermediate SHC (23.6 cm/d); 

these findings are consistent with the observation that samples 

with a mostly silt and clay matrix generally have low porosity 

and low to intermediate SHC.

The highest SHC in the member (38 cm/d) is from moderately consolidated sandstone in the middle part of the member (sample 10-RP-4; fig. 16) and, like sample 10-RP-10, has 

abundant fracture porosity and moderate amounts of moldic 

and intercrystalline pore space. Sample RP-12-15, from the 

Figure 14. Conglomeratic sandstone (with mudcracks) in the 

middle part of the Nogales Wash member; global positioning 

system (GPS) unit for scale. This rock (sample RP-12-46; site 13 

on fig. 4) has a low porosity at 22 percent, a low bulk density at 

1.76 grams per cubic centimeter, and an intermediate saturated 

hydraulic conductivity at 23.6 centimeters per day. Thin sections 

show an abundant clay and silt matrix with some moldic pore 

space but minimal to no intercrystalline pore space.

Figure 15. Thin section of 

conglomeratic sandstone (sample 

RP-12-46; site 13 on fig. 4) from 

the middle part of the Nogales 

Wash member showing mostly 

quartz, plagioclase, and biotite 

framework grains in a clay and silt 

matrix. Note some moldic porosity 

but little to no intercrystalline 

pore space. See figure 14 for 

photograph of outcrop. Cross 

nicols polarized light. (mm, 

millimeter)

1.0 millimeter

Q Q

Q

P

P

B

P Plagioclase

Q Quartz

B Biotite

EXPLANATION

Q

P

Q

Q

P Plagioclase

Q Quartz

B Biotite

EXPLANATION

Q
16 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Figure 17. Massive clay unit in the Mariposa member between 

Interstate 19 and Grand Avenue, south of Mariposa Road. Unit 

may be a significant local confining unit in the Mariposa member, 

although its subsurface thickness and lateral extent are poorly 

known. Note the unit holding water following a rainstorm.

upper part of the member, has an intermediate SHC at 26 cm/d 

and is from fine-grained, moderately sorted sandstone near 

the top of the member. Thin sections show a mostly pumice 

and glass matrix with moderate intercrystalline pore space and 

minor amounts of moldic pore space.

Sample RP-12-24 is from sandstone near the top of the 

member at Crawford Hill, along Interstate 19 (fig. 2), which 

contains mostly pumice, volcanic clasts, and chert. The sample 

has low porosity (22 percent) and intermediate bulk density 

(1.86 gm/cm3). Thin sections show a pumice and glass matrix 

and abundant moldic and intercrystalline pore space; parts of 

the matrix are altered to clay.

Mariposa Member

The Mariposa member contains alternating beds of conglomerate, conglomeratic sandstone, siltstone, and claystone. 

Claystone units are exposed in the lower part of the member 

in the Mariposa Road area, between Interstate 19 and Grand 

Avenue (fig. 17). The claystone may be a confining unit within 

the member, but more subsurface data are needed to determine 

its subsurface distribution and thickness. The claystone is massive bedded and is estimated to be greater than 60 m (Page and 

others, 2016). Similar claystone units are exposed in the area 

east of the Santa Cruz River and south of Sonoita Creek but 

are generally thinner than the Mariposa Road units.

Four samples of the Mariposa member were analyzed 

for porosity, and three samples for SHC. Porosity is low to 

intermediate and ranges from 16 to 36 percent (table 2), and 

bulk density is low to intermediate and ranges from 1.6 to 

Figure 16. Alternating thin- to thick-bedded sandstone and 

conglomeratic sandstone of the Nogales Wash member south of 

Mariposa Road and west of Grand Avenue. A small displacement 

fault diagonally cuts the beds. Sandstone from this location 

(sample 10-RP-4; site 8 on fig. 4) has the highest saturated 

hydraulic conductivity for the member at 38 centimeters per day.

2.37 g/cm3 (table 2). Saturated hydraulic conductivity for the 

member is also low to intermediate compared to other members and ranges from 5.6 to 33.4 cm/d (table 3).

Both the highest and lowest porosity are from sandstone 

in the upper part of the member (fig. 2–1F), east of the Santa 

Cruz River and south of Sonoita Creek (figs. 2, 4). Sample 

RP-12-27 has the highest porosity (36 percent) and highest 

bulk density at (2.37 g/cm3) for the member, as well as a moderately high SHC (32.7 cm/d). The sample is from conglomeratic sandstone (fig. 18), and thin sections show abundant 

moldic and intercrystalline pore space with a matrix of small 

disaggregated pumice and glass fragments. Scanning electron 

microscope and x-ray diffraction methods indicate that the 

sample contains abundant clinoptilolite and lesser smectite, 

and SEM (fig. 19) shows moderate to abundant amounts of 

intercrystalline pore space between clinoptilolite crystals, 

which may explain the moderately high porosity and SHC.

Sample RP-12-11 is also from the upper part of the member and has the lowest porosity of the entire Nogales Formation at 16 percent. It was collected from fine-grained facies of 

the member, which consist of sequences of sandstone, siltstone, and claystone (fig. 20). Thin sections show a mostly silt 

and clay matrix (fig. 21), calcite filling some pore space, and 

minor intercrystalline and moldic porosity. The sample has 

intermediate bulk density at 2.07 g/cm3.

Sample 10-RP-2 was collected from a thin sandstone 

bed in the lower part of the member (fig. 22), in the Mariposa 

Road area. The sample has low porosity (24 percent), the lowest bulk density (1.6 g/cm3

) for the entire formation, and an 

intermediate SHC (33.4 cm/d). Thin sections show a mostly 
Discussion of Analyses by Nogales Formation Member 17

Figure 18. Mariposa member east of the Santa Cruz River 

and south of Sonoita Creek; hammer and notebook for scale. 

Sandstone from this location (sample RP-12-27; site 6 on fig. 4) 

has the highest effective porosity for the member at 36 percent 

and the highest bulk density for the member at 2.37 grams per 

cubic centimeter; it has a moderately high saturated hydraulic 

conductivity at 32.7 centimeters per day. 

Figure 19. Scanning electron microscope image of sandstone (sample RP-12-27; site 6 on fig. 4) from the 

Mariposa member. Larger framework grains (mostly quartz) are separated by intercrystalline pore space filled 

with mostly clinoptilolite crystals and some fibrous organic material. Pore space is generally 50 micrometers

(μm) and less in width. See figure 18 for photograph of outcrop.

Q Quartz

C Clinoptilolite

O Organic material

EXPLANATION

O Q Q

Q

C

C

C

C

C

O

Q Quartz

C Clinoptilolite

O Organic material

EXPLANATION

O Q Q

Q

C

C

C

C

C

O

silt and clay matrix, moderate amounts of intercrystalline 

pore space, minor fracture porosity, and some large pumice 

fragments with moderate moldic porosity. X-ray diffraction 

indicates that the sample contains abundant smectite and 

minor clinoptilolite.

Sample RP-12-19a from near the base of the member 

has low porosity (21 percent), moderately high bulk density 

(2.23 g/cm3), and the lowest SHC for the member (5.6 cm/d). 

Thin sections show the rock is moderately sorted and fine 

grained with a mostly pumice matrix, moderate amounts of 

moldic porosity within pumice fragments, and minor intercrystalline pore space. Fabric characteristics are similar to the 

only other moderately sorted, fine-grained sample analyzed 

(RP-12-7 from the Proto Canyon member), which also has a 

low porosity at 22 percent. 
18 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Fractures in the Nogales Formation

All members of the Nogales Formation are fractured 

and faulted from Tertiary Basin and Range extensional 

deformation, which was contemporaneous with deposition 

of the formation. Fractures are present in all members of the 

formation in the Nogales, Ariz., area, but the Nogales Wash 

member is pervasively fractured compared to the other members. Subvertical, open fractures are present in the Mariposa 

member, especially in road cuts along Interstate 19 north of 

Mariposa Road (fig. 23). The Nogales Formation is moderately to highly fractured in other parts of the upper Santa Cruz 

basin, including the Agua Fria Canyon area (figs. 24) and the 

Peña Blanca Canyon area (fig. 25), both in the Peña Blanca 

Lake 7.5’ quadrangle (fig. 1). The Nogales Formation in Agua 

Fria Canyon contains intersecting northwest- and northeasttrending fractures in volcaniclastic sandstone units. Outcrops 

in the Peña Blanca Canyon area show abundant intersecting 

fractures in a distinctive, highly brittle ash fall tuff unit in the 

Nogales Formation. 

Fractures in the Nogales Wash and Proto Canyon members are well exposed in several outcrops in the Nogales, Ariz., 

area, including in urban Nogales, and the Sonoita Creek area; 

see figure 4 for outcrop locations. We mapped fractures and 

produced simplified maps of several outcrops using Google 

Earth imagery (figs. 26, 27), primarily to demonstrate that 

many parts of the Nogales Formation are fractured in outcrop and that these fracture networks show connectivity in 

the upper Santa Cruz basin. Although these reconnaissance 

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_22.ai

Figure 22. Thin sandstone bed (7 centimeters thick; outlined by 

bracket) in Mariposa member. Rock from this bed (sample 10-RP-2; 

site 1 on fig. 4) has a low porosity at 24 percent, the lowest bulk 

density for the entire formation at 1.6 grams per cubic centimeter, 

and an intermediate saturated hydraulic conductivity at 33.4 

centimeters per day. The rock has a mostly silt and clay matrix and 

moderate amounts of intercrystalline and moldic porosity.

Figure 20. Fine-grained facies of the Mariposa member, south of 

Sonoita Creek, east of the Santa Cruz River, and near the Mount 

Benedict fault, consisting of alternating beds of fine-grained 

volcaniclastic sandstone, siltstone, and claystone; hammer for 

scale. Sandstone from this location (sample RP-12-11; site 4 on 

fig. 4) has the lowest porosity for the entire Nogales Formation 

at 16 percent. Thin sections (fig. 21) show a mostly silt and clay 

matrix, calcite filling the pore space, and minor intercrystalline 

and moldic porosity.

Figure 21. Thin section of sandstone (sample RP-12-11; site 4 on 

fig. 4) from the Mariposa member, south of Sonoita Creek, east of 

the Santa Cruz River, and near the Mount Benedict fault, showing 

a predominantly silt and clay matrix and silt-size grains composed 

primarily of subangular quartz and minor biotite, hornblende, 

and plagioclase; several larger, rounded porphyritic volcanic 

grains are to the left of scale bar. See figure 20 for photograph of 

outcrop. Cross nicols polarized light. (mm, millimeter)
Fractures in the Nogales Formation 19

studies are mainly for demonstration purposes, comprehensive 

fracture investigations are needed to better understand and 

fully evaluate fracture flow in the upper Santa Cruz basin. 

Future studies should include detailed fracture mapping and 

description of fracture characteristics important to hydrologic 

flow modeling, including fracture orientation (azimuth, dip, 

and dip direction), fracture surface roughness, aperture, trace 

length, spacing, and connectivity. These types of studies were 

completed for hydrogeologic modeling in other parts of the 

Basin and Range Province (for example, Barton and others, 

1993), where Tertiary volcanic rocks have also been deformed 

by episodes of Basin and Range extension.

Figure 23. Fractures in volcaniclastic sandstone and 

conglomerate of the Mariposa member north of Mariposa Road 

and west of Interstate 19.

Figure 24. North-to-northeast view of intersecting fractures 

(indicated by linear vegetation patterns) in volcaniclasitc 

sandstone of the Nogales Formation in the Agua Fria Canyon area. 

Width of view is about 250 meters across.

Figure 25. Aerial view of highly fractured outcrop in ash fall tuff 

unit in the lower part of the Nogales Formation in the Peña Blanca 

Lake 7.5’ quadrangle (fig. 1). State Highway 289 is shown near top 

of image. Top of image is north; width of view is about 175 meters 

across. (Image from Google, 2014)

One prominent outcrop in the Nogales Wash member 

is northeast of where State Highway 82 joins Grand Avenue 

(figs. 2, 26); the outcrop contains at least four main fracture 

sets, including east-northeast (yellow), north-northeast (blue), 

northeast (green), and northwest (red) trending sets. Northnortheast and northeast sets contain the longest through-going 

fractures. North-northeast fractures are the longest, do not abut 

other fractures, and cut shorter fractures of the northwest and 

east-northeast sets. Northeast fractures have long trace lengths, 

abut fractures in the north-northeast and northwest sets, and 

intersect northwest fractures. Northwest fractures have some 

long trace lengths, but they also have shorter fractures which 

are bound by and break up smaller blocks between longer 

north-northeast and northeast fractures. The east-northeast 

set contains the shortest fractures, which also break up blocks 

between the longer through-going sets.

In the Sonoita Creek area (fig. 27), three fracture sets 

were mapped in the lower part of the Proto Canyon member: east-northeast (yellow), north-northwest (blue), and 
20 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Figure 26. Aerial view of simplified fracture map of the Nogales Wash member of the 

Nogales Formation northeast of where State Highway 82 joins Grand Avenue. Top of image 

is north. (Base map from Google, 2015)

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_26.ai

0 20 40 60 80

0 10 20

100 FEET

30 METERS

East-northeast fracture set

EXPLANATION

North-northeast fracture set

Northeast fracture set

Northwest fracture set
Fractures in the Nogales Formation 21

Figure 27. Aerial view of simplified fracture map of the Proto Canyon member of the Nogales Formation in the 

Sonoita Creek area. West-northwest fractures are the dominant set. Top of image is north. (Base map is from 

Google, 2015)

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\figure_27.ai

0 50 100 150

0 25

200 FEET

50 METERS

East-northeast fracture set

EXPLANATION

North-northwest fracture set

West-northwest fracture set
22 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

west-northwest (red) sets. The north-northwest set contains the 

longest through-going fractures and intersects fractures of the 

west-northwest set. The west-northwest set also has some long 

fractures, but it has shorter fractures which are bound by the 

longer north-northwest set and break up into smaller blocks 

between the longer fractures. The east-northeast fractures are 

similar to those in the Nogales area outcrop and have similar 

orientations; they generally include smaller fractures which 

break up blocks between longer through-going fractures.

Summary

New hydrogeologic investigations of the Nogales Formation were conducted to better understand and evaluate the 

groundwater resource potential of the Nogales Formation in 

the Nogales, Arizona, area. Preliminary results of these investigations suggest that parts of the Miocene Nogales Formation 

may be new, deeper sources of groundwater for the area. Our 

studies are based primarily on detailed geologic mapping and 

geophysical interpretations of the formation in the Rio Rico 

and Nogales 7.5’ quadrangles (Page and others, 2016). 

We analyzed sandstone samples from the formation for 

porosity, bulk density, saturated hydraulic conductivity (SHC), 

and fabric. Effective porosity ranges from 16 to 42 percent, 

bulk density from 1.6 to 2.47 grams per cubic centimeter, and 

SHC from 4 to 57 centimeters per day. Thin sections indicate a 

matrix in most samples that consists of disaggregated pumice 

and volcanic glass fragments; some samples contain predominantly silt and clay. Samples with a mostly silt and clay matrix 

generally have a lower porosity and SHC compared to samples 

with a mostly pumice and glass matrix, which generally have a 

higher porosity and SHC but at much wider ranges.

Most sandstone in the formation is poorly sorted, but 

several samples are moderately sorted, consist of fine-grained 

sandstone, and generally have low porosity. Pore space in the 

Nogales Formation sediments generally included moldic, intercrystalline, and fracture porosity. Some intercrystalline pore 

space is partially filled with calcite cement. About one third of 

the samples show fracture porosity, which corresponds to the 

fracturing noted in outcrops in all members of the formation.

Scanning electron microscope and x-ray diffraction 

analyses indicate that most of the samples contained the zeolite clinoptilolite and varying amounts of mixed-layer smectite 

and illite clay. Samples with greater amounts of clinoptilolite 

and lesser amounts of smectite have high porosity and SHC, 

in narrow ranges. Samples with abundant amounts of smectite 

and lesser amounts of clinoptilolite have wide-ranging porosity and SHC, which span the entire ranges of porosity and 

SHC values reported for the entire formation. 

All members of the Nogales Formation are fractured and 

faulted as a result of Tertiary Basin and Range extensional 

deformation, which was broadly contemporaneous with deposition of the Nogales Formation. Fractures are present in all 

members of the formation, but the Nogales Wash member is 

pervasively fractured compared to the other members. These 

structures may have significant influence on groundwater flow 

in the upper Santa Cruz basin.

Acknowledgments

We thank Margaret E. Berry and Harland Goldstein 

(USGS Geoscience and Environmental Change Science Center, 

Denver, Colorado) for their reviews; their comments and 

suggestions vastly improved the report. Gary Skipp (USGS, 

Denver, Colo.) analyzed samples from the Nogales Formation 

using x-ray diffraction. Heather Lowers (USGS, Denver, Colo.) 

prepared samples and assisted the senior author in analyzing 

samples from the Nogales Formation using the scanning electron microscope. Michelle Stern of the USGS California Water 

Science Center (USGS Hydrologic Research Laboratory, Sacramento, Calif.) analyzed samples from the Nogales Formation 

for porosity, saturated hydraulic conductivity, and bulk density. 

Wagner Petrographic (Lindon, Utah) prepared all thin sections 

for fabric studies of the Nogales Formation.

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Appendixes
26 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Appendix 1. Thin Section Analyses of the Nogales Formation

RP-12-27—Mariposa member, south end of exposed Mount 

Benedict fault; sample site 6; volcaniclastic sandstone, 

subrounded to subangular, poorly sorted; quartz, plagioclase, pumice, volcanic glass, biotite, hornblende, volcanic 

porphyritic grains with biotite and hornblende, opaques, 

and chert; matrix pumice and volcanic glass fragments; 

abundant moldic and intercrystalline porosity; minor calcite 

in pore space; clay replacing highly altered plagioclase and 

pumice grains. 

RP-12-29—Mariposa member, fine-grained facies south of 

Sonoita Creek and east of Santa Cruz River; sample site 7; 

volcaniclastic sandy claystone to clayey sandstone and conglomerate, subrounded to subangular, poorly sorted; quartz, 

highly altered plagioclase, biotite, pumice, volcanic glass, 

porphyritic volcanic grains with highly altered biotite, and 

opaques; matrix mostly iron-stained silt and clay, and some 

pumice and glass fragments; abundant fracture, intercrystalline, and moldic porosity; calcite cement filling intercrystalline pore space.

Nogales Wash Member

10-RP-4—Nogales Wash member, west side of Grand 

Avenue south of Mariposa Road, Nogales, Ariz.; sample 

site 8; volcaniclastic sandstone, subangular to subrounded, 

poorly sorted; pumice and volcanic glass fragments, quartz, 

plagioclase, biotite, hornblende, spherulites, large volcanic 

porphyritic grains with plagioclase, biotite, and hornblende; 

matrix pumice and volcanic glass fragments; abundant fracture porosity, moderate intercrystalline and moldic porosity.

10-RP-10—Nogales Wash member, Grand Avenue area south 

of Mariposa Road, Nogales, Ariz.; sample site 9; volcaniclastic sandstone and conglomerate, subangular to subrounded, 

poorly sorted; pumice and volcanic glass fragments, quartz, 

lesser plagioclase, small volcanic porphyritic grains with 

plagioclase laths, biotite, hornblende, opaques, microcline, 

and chert; matrix mostly pumice and volcanic glass fragments, with some silt and clay; abundant fracture porosity, 

moderate moldic and intercrystalline porosity.

RP-12-15—Nogales Wash member, near the international border; sample site 10; volcaniclastic sandstone, fine-grained, 

subangular to subrounded, moderately sorted; pumice and 

volcanic glass fragments, equal amounts of smaller crystals 

of subangular quartz and plagioclase, biotite, hornblende, 

chert, volcanic porphyritic grains with plagioclase laths, 

and some opaque grains in pore space; matrix pumice and 

volcanic glass fragments, and grain-supported where matrix 

absent; moderate intercrystalline and minor moldic porosity.

Mariposa Member

10-RP-2—Mariposa member, along Mariposa Road between 

Interstate 19 and Grand Avenue, Nogales, Ariz.; sample site 

1; volcaniclastic conglomerate and sandstone, subangular to 

subrounded, poorly sorted; quartz, plagioclase, microcline, 

large pumice fragments, biotite, hornblende, small scattered 

opaques, and some rounded clay; grains highly altered to 

clay; matrix mostly silt and clay, and some pumice and volcanic glass fragments; moderate moldic and intercrystalline 

porosity and minor fracture porosity.

10-RP-9—Mariposa member, along Mariposa Road west of 

Grand Avenue, Nogales, Ariz.; sample site 2; volcaniclastic 

conglomerate and sandstone, subrounded to subangular, 

poorly sorted; quartz (larger grains polymictic), highly 

altered plagioclase, pumice, volcanic glass, hornblende, biotite, chert, and opaques; matrix pumice and volcanic glass 

fragments, and some silt and clay; moderate intercrystalline, 

moldic, and fracture porosity; clay replacing highly altered 

grains and calcite filling some pore space. 

RP-12-9—Mariposa member, Sonoita Creek area; sample 

site 3; volcaniclastic conglomerate and sandstone, bimodal 

and poorly sorted; large grains subrounded, highly altered 

hornblende, plagioclase- and biotite-bearing porphyritic volcanic rocks, and some pumice and volcanic glass fragments; 

smaller grains mostly subrounded and poorly sorted quartz, 

plagioclase, hornblende, and biotite; matrix mostly grain 

supported, but some pumice and volcanic glass fragments, 

silt, and clay; moderate intercrystalline and minor moldic 

porosity; abundant secondary calcite filling intercrystalline 

pore space.

RP-12-11—Mariposa member, near exposed Mount Benedict fault; sample site 4; volcaniclastic sandstone, fine- to 

coarse-grained, subrounded to subangular, poorly sorted; 

quartz, plagioclase, biotite, and subrounded pumice and 

volcanic glass fragments, some volcanic porphyritic grains 

with hornblende and biotite, spherulites, and some opaque 

grains; contains thin clay layers; matrix mostly silt and 

clay, and some pumice and volcanic glass; minor moldic 

and intercrystalline porosity; minor secondary calcite and 

opaques filling intercrystalline pore space. 

RP-12-19a—Mariposa member (base of member), east of 

Nogales, Ariz., near the international border; sample site 

5; volcaniclastic sandstone, fine-grained, subrounded to 

subangular, moderately sorted; mostly pumice and volcanic 

glass fragments with lesser quartz, plagioclase, hornblende, 

biotite, chert, and scattered opaques; matrix pumice and 

volcanic glass fragments, and grain supported where matrix 

absent; moderate moldic and minor intercrystalline porosity. 
Appendix 1 27

RP-12-16—Nogales Wash member (lower to basal part of 

member), east of Nogales, Ariz., near the international border; sample site 11; volcaniclastic sandstone, fine-grained, 

subangular to subrounded, moderately sorted; pumice and 

volcanic glass, equal amounts of quartz and plagioclase, 

biotite, microcline, hornblende, scattered opaques, and some 

opaques replacing biotite; matrix pumice and volcanic glass 

fragments, and some grain-supported layers with minor 

hematite where matrix is absent; moderate moldic and intercrystalline porosity.

RP-12-24—Nogales Wash member, Crawford Hill road cut; 

sample site 12; volcaniclastic sandstone and conglomerate, subrounded to subangular, very poorly sorted; volcanic 

porphyritic grains with plagioclase and hornblende, quartz, 

plagioclase, hornblende, sanidine, pumice and volcanic 

glass, rounded chert, spherulites, and some opaques; matrix 

mostly pumice and volcanic glass fragments; abundant 

moldic and intercrystalline porosity.

RP-12-46—Nogales Wash member, City Hall, Grand Avenue, 

Nogales, Ariz.; sample site 13; conglomeratic sandstone, 

subangular to subrounded, very poorly sorted; quartz, 

plagioclase, bitotite, large rounded iron-stained quartzose 

sandstone clasts, and granitic porphyritic clasts; matrix 

mostly clay and silt; minor moldic porosity and minimal to 

no intercrystalline pore space.

Proto Canyon Member

10-RP-3—Proto Canyon member, north of Mariposa Road 

between Grand Avenue and Interstate 19, Nogales, Ariz.; 

sample site 14; volcaniclastic sandstone, subangular to subrounded, poorly sorted; mostly quartz (some larger grains 

polymictic), plagioclase, lesser microcline, biotite, hornblende, volcanic porphyritic grains with biotite, pumice, 

and opaques; matrix pumice and volcanic glass fragments; 

moderate to abundant fracture, intercrystalline, and moldic 

porosity.

RP-12-4a—Proto Canyon member, east side of Grande Avenue north of Mariposa Road, Nogales, Ariz.; sample site 15; 

volcaniclastic sandstone and conglomerate, subangular to 

subrounded, poorly sorted; coarse polymitic strained quartz 

and plagioclase (undulose extinction), biotite, hornblende, 

pumice and volcanic glass fragments, and volcanic porphyritic grains with biotite, hornblende, and some plagioclase; 

matrix mostly silt and clay, with some pumice and volcanic 

glass; abundant fracture porosity, minor intercrystalline and 

moldic porosity; moderate to abundant calcite filling intercrystalline pore space, clay replacing large corroded grains 

of quartz and plagioclase. 

RP-12-7—Proto Canyon member, Sonoita Creek area; sample 

site 17; volcaniclastic sandstone, fine-grained, mostly subrounded, moderately sorted; pumice and volcanic glass fragments, volcanic porphyritic grains with biotite and quartz, 

lesser quartz, plagioclase, biotite, hornblende, and microcline; matrix pumice and volcanic glass fragments; moderate moldic and moderate to abundant micro-intercrystalline 

porosity between small, disaggregated pumice fragments.

RP-12-8—Proto Canyon member, Sonoita Creek area; sample 

site 18; volcaniclastic conglomerate and sandstone, poorly 

sorted; mostly pumice and large volcanic porphyritic grains 

with highly altered plagioclase, lesser subangular quartz, 

plagioclase, hornblende, biotite, opaques, and chert; matrix 

mostly pumice and volcanic glass fragments; moderate 

moldic and minor intercrystalline porosity.

RP-12-14—Proto Canyon member, east of Nogales, Ariz., 

along the international border; sample site 19; volcaniclastic sandstone and pebble conglomerate, subangular, poorly 

sorted; mostly pumice and volcanic glass, equal amounts of 

highly altered quartz and plagioclase, biotite, hornblende, 

and volcanic porphyritic grains with plagioclase laths; 

matrix silt, clay, and pumice; moderate moldic and minor 

intercrystalline porosity.

RP-12-21—Proto Canyon member, Proto Canyon; sample site 

20; volcaniclastic sandstone and conglomerate, subangular, 

poorly sorted; large pumice fragments, subangular quartz, 

biotite, plagioclase, hornblende, chert, and claystone; matrix 

mostly pumice and volcanic glass fragments; moderate 

moldic and minor intercrystalline porosity.

RP-12-32—Proto Canyon member, Proto Canyon area; 

sample site 21; volcaniclastic sandstone, subangular to 

subrounded, poorly sorted; quartz, plagioclase, pumice, 

hornblende, biotite, opaques, porphyritic volcanic fragments, and chert; matrix combination of silt, clay and 

pumice; includes silt and clay layers; moderate moldic and 

minor intercrystalline porosity.

RP-12-42a—Proto Canyon member, Yerba Buena Canyon; 

sample site 22; volcaniclastic sandstone, subangular to 

subrounded, poorly sorted; pumice, quartz, plagioclase 

(highly altered to clay), porphyritic volcanic fragments, 

biotite, hornblende, chert, quartzose sandstone fragments, 

and opaques; matrix combination of pumice, silt, and clay; 

moderate moldic and minor intercrystalline porosity.
28 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

Appendix 2. Values of Bulk Density, Effective Porosity, and Saturated Hydraulic 

Conductivity For the Nogales Formation

Figure 2–1. Plots of bulk density, effective porosity, and saturated hydraulic conductivity (SHC) for the Nogales Formation, by 

member. A, Bulk density for all members of the Nogales Formation. B, Effective porosity for the Proto Canyon member. C, SHC 

for the Proto Canyon member. D, Effective porosity for the Nogales Wash member. E, SHC for the Nogales Wash member. 

F, Effective porosity for the Mariposa member. G, SHC for the Mariposa member.

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\plot_01.ai

A

RP-12-21RP-12-32

RP-12-42a

RP-12-14

RP-12-7

RP-12-4a

RP-12-46RP-12-24

RP-12-19a

10-RP-2

RP-12-27RP-12-11

10-RP-3

10-RP-10

3

2

1.5

1

0.5

0

Bulk density, in grams per cubic centimeter

Sample number

lower middle upper lower middle upper lower upper

Nogales Formation

2.5

Proto Canyon member Nogales Wash member Mariposa member
Appendix 2 29

Figure 2–1.—Continued Plots of bulk density, effective porosity, and saturated hydraulic conductivity (SHC) for the Nogales 

Formation, by member. A, Bulk density for all members of the Nogales Formation. B, Effective porosity for the Proto Canyon 

member. C, SHC for the Proto Canyon member. D, Effective porosity for the Nogales Wash member. E, SHC for the Nogales Wash 

member. F, Effective porosity for the Mariposa member. G, SHC for the Mariposa member.

6_cmrl00_0034_sir_page\report_figures\plot_02.ai

B

RP-12-21RP-12-32

RP-12-42a

RP-12-14

RP-12-7

RP-12-4a

10-RP-3

45

40

35

30

25

20

15

10

5

0

Effective porosity, in percent

Sample number

lower part middle part upper part

Proto Canyon member

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\plot_03.ai Saturated hydraulic conductivity, in centimeters per day RP-12-21

RP-12-32

RP-12-42a

RP-12-7

RP-12-4aRP-12-4b

10-RP-3

60

50

40

30

20

10

0

Sample number

lower part middle part upper part

Proto Canyon member

C

10-RP-10RP-12-46RP-12-24

45

40

35

30

25

20

15

10

5

0

Effective porosity, in percent

Sample number

lower part middle

part

upper part

Nogales Wash member

D

Saturated hydraulic conductivity, in centimeters per day

10-RP-4

RP-12-46RP-12-15

60

50

40

30

20

10

0

Sample number

middle part upper part

Nogales Wash member E
30 Hydrogeologic Investigations of the Miocene Nogales Formation in the Nogales Area, Upper Santa Cruz Basin, Arizona

l00_0034_sir_page\report_figures\plot_06.ai

RP-12-19a

10-RP-2

RP-12-27RP-12-11

45

40

35

30

25

20

15

10

5

0

Effective porosity, in percent

Sample number

lower part upper part

Mariposa member

F

\\IGSKAHCMVSFS002\Pubs_Common\Jeff\den16_cmrl00_0034_sir_page\report_figures\plot_07.ai Saturated hydraulic conductivity, in centimeters per day

RP-12-19a

RP-12-27

10-RP-2

60

50

40

30

20

10

0

Sample number

lower part upper part

Mariposa member G

Figure 2–1.—Continued Plots of bulk density, effective porosity, and saturated hydraulic conductivity (SHC) 

for the Nogales Formation, by member. A, Bulk density for all members of the Nogales Formation. B, Effective 

porosity for the Proto Canyon member. C, SHC for the Proto Canyon member. D, Effective porosity for the 

Nogales Wash member. E, SHC for the Nogales Wash member. F, Effective porosity for the Mariposa member. 

G, SHC for the Mariposa member.
Appendix 3 31

Appendix 3. Porosity, Saturated Hydraulic Conductivity, and Bulk Density 

Analyses and Scanning Electron Microscope and X-Ray Diffraction Methods

Porosity, Bulk Density, and Saturated Hydraulic Conductivity

Samples for porosity, bulk density, and saturated hydraulic conductivity (SHC) were analyzed by the U.S. Geological Survey (USGS) Hydrologic Research Laboratory (HRL) in Sacramento, California. For a detailed summary of the physical properties methods used, see USGS Technical Procedure USGS-HP-229, R3. Determinations of gravimetric and volumetric water 

content and of bulk density, porosity, and particle density were obtained using a saturation chamber and a laboratory drying oven 

and were calibrated using balances and Archimedes methods.

Effective porosity (in percent) was calculated by the equation 

Effective porosity = Porosity – Residual water content

where Relative humidity dry weight (g) Oven dry weight (g) Residual water content = 

Sample bulk volume

− .

The relative humidity dry weight (in grams) was measured at 60 °C and 65 percent humidity. Bulk density (in grams per cubic 

centimeter) was calculated as dry weight over sample bulk volume. Data on SHC were collected from the Tri-flex 2 Permeameter in accordance with the American Society for Testing and Materials Procedure D5084; conductivities were corrected to 

20 °C. All measurement devices were calibrated to National Institute of Standards and Technology traceable standards, and a 

documented quality assurance program at the USGS HRL ensured minimal error in the measurements.

Scanning Electron Microscope

For scanning electron microscope (SEM) analyses, rock chips were mounted on carbon tape adhered to an aluminum 

sample stub and coated with carbon for conductivity. The rock chips were placed in a JEOL 5800LV scanning electron microscope operated at 15 kilovolts and a 1-nanoampere current at high vacuum. The chips were examined in both secondary and 

backscattered electron imaging modes. Qualitative chemistry was acquired from spots of interest with a Thermo Fisher silicon 

drift detector and USGS National Streamflow Statistics software (http://water.usgs.gov/software/NSS/).

X-Ray Diffraction

For x-ray diffraction (XRD) analyses, clay separation and preparation included removing a representative split of each 

sample, which was disaggregated and placed in a beaker with distilled water and placed in an ultrasonic for 4–6 minutes. 

Suspended material was decanted into 250-milliliter centrifuge bottles and centrifuged at the appropriate speed and time for a 

<2-micrometer size separation. The clay size separation was then mounted on a glass slide according to the preparation of Pollastro (1982) using the Millipore filter transfer method. Clay mounts were analyzed after they were air-dried, glycolated, and 

heated to 550 °C. The XRD analyses were performed on a Philips 3600 diffractometer using copper radiation. Operating conditions were 30 milliamperes and 40 kilovolts. X-ray diffraction data were collected at 0.02° 2 Ɵ steps using a 2-second dwell per 

step. Oriented clay mounts were scanned from 2 to 35° 2 Ɵ.

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ISSN 2328-0328 (online)

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Page and others—Hydrogeologic Investigations of the Miocene Nogales Formation, Nogales Area, Upper Santa Cruz Basin, Arizona—SIR 2016–5087