United States–Mexican

. . . . .facing tomorrow’s challenges through USGS science

Circular 1380

U.S. Department of the Interior

U.S. Geological Survey

Borderlands

. . . . .facing tomorrow’s challenges through USGS science

United States–Mexican

Edited by 

Randall G. Updike, Eugene G. Ellis, 

William R. Page, Melanie J. Parker, Jay B. Hestbeck, 

and William F. Horak

Graphic design and layout by 

Carol A. Quesenberry

Borderlands

Circular 1380

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2013

For more information on the USGS—the Federal source for science about the Earth,

its natural and living resources, natural hazards, and the environment—visit 

http://www.usgs.gov or call 1–888–ASK–USGS

For an overview of USGS information products, including maps, imagery, and publications,

visit http://www.usgs.gov/pubprod

To order this and other USGS information products, visit http://store.usgs.gov

Suggested citation:

Updike, R.G., Ellis, E.G., Page, W.R., Parker, M.J., Hestbeck, J.B., and Horak, W.F., eds., 

2013, United States–Mexican Borderlands—Facing tomorrow’s challenges through USGS science: 

U.S. Geological Survey Circular 1380, 336 p., 1 pl.

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government.

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report.

Library of Congress Cataloging-in-Publication Data

United States–Mexican borderlands : facing tomorrow’s challenges through USGS science / edited by Randall G. Updike, Eugene G. Ellis, 

 William R. Page, Melanie J. Parker, Jay B. Hestbeck, and William F. Horak ; graphic design and layout by Carol A. Quesenberry.

 pages cm. – (Circular ; 1380)

Includes bibliographical references.

ISBN 978-1-4113-3517-2 (pbk.)

1. Environmental protection–United States. 2. Environmental protection–International cooperation. 3. Mexican–American Border Region–

 Environmental conditions. 4. Geological Survey (U.S.)–Research. 5. Environmental sciences–Research–United States. 6. Environmental policy–

 United States. 7. Environmental policy–Mexico. I. Updike, Randall G. II. Ellis, Eugene G. III. Page, William R. IV. Parker, Melanie J. V. Hestbeck, 

 Jay Brian. VI. Horak, W. F. VII. Geological Survey (U.S.) 

TD23.U56 2012

333.70972’1–dc23

 2012045601
Chapter 1

The United States–Mexican Border—

A Land of Conflict and Opportunity 

By Randall G. Updike

Challenges of the Borderlands................................................................................................................ 10

Figures

1–1. Map showing examples of boundaries defining the Borderlands, the immediate 

area in both countries adjacent to the United States–Mexican border ................................. 3

Table of Contents

2
iv 

Chapter 2

The Borderlands—A Region of Physical and 

Cultural Diversity

By Jean W. Parcher, Diana M. Papoulias, Dennis G. Woodward, and Roger A. Durall

Subarea 1. Pacific Basins and Salton Trough ................................................................................... 18

Subarea 2. Colorado River and Gulf of California ............................................................................. 20 

Subarea 3. Mexican Highlands............................................................................................................ 22

Subarea 4. San Basilio and Mimbres.................................................................................................. 24

Subarea 5. Rio Grande West—Elephant Butte Reservoir to Rio Conchos ................................... 26

Subarea 6. Rio Grande Central—Rio Conchos to Amistad Reservoir........................................... 30

Subarea 7. Rio Grande East—Below Amistad Reservoir to Falcon Reservoir............................ 34

Subarea 8. Lower Rio Grande Valley................................................................................................... 36

Figures

2–1. Map showing the eight subareas of the United States–Mexican border region ................ 15

2–2. Map showing physiographic and geologic features of the United States–Mexican 

border region................................................................................................................................... 16

2–3. Map showing the Pacific Basins–Salton Trough subarea and the Colorado River–

Gulf of California subarea, with United States and Mexican agency land holdings 

and protected areas....................................................................................................................... 21

2–4. Map showing the Mexican Highlands subarea and the San Basilio–Mimbres subarea, 

with United States and Mexican agency land holdings and protected areas............................ 25

2–5. Map showing the Rio Grande West subarea and the Rio Grande Central subarea, 

with United States and Mexican agency land holdings and protected areas ......................... 32

2–6. Map showing the Rio Grande East subarea and the Lower Rio Grande Valley subarea, 

with United States and Mexican agency land holdings and protected areas..................... 37

Tables

2–1. Information on sister cities, major urban areas, and population; economic activities; 

and land use for the eight subareas of the United States–Mexican border region............ 38

2–2. Physiographic provinces, ecoregions, and climate types included in the eight 

subareas of the United States–Mexican border region .......................................................... 39

2–3. Border length, watershed area, major hydrologic features, and elevation ranges 

for the eight subareas of the United States–Mexican border region.................................... 40

14
 v

Chapter 3

Challenge Theme 1. Understanding and Preserving 

Ecological Resources

By J. Bruce Moring, Diana M. Papoulias, and Charles van Riper III

Background. ................................................................................................................................................ 42

Biological Status and Trends ................................................................................................................... 44

 Capabilities................................................................................................................................... 60

A Migrant Bird’s Dilemma......................................................................................................................... 46

Bears and Sky Islands in the Southwest ............................................................................................... 50

Salt Cedar and the Forgotten Reach ...................................................................................................... 58

Figures

3–1. Map showing ecological regions along the United States–Mexican border ...................... 43

3–2. Photo of a lesser long-nosed bat preparing to collect nectar from a saguaro.................... 45

3–3. Photo of ocelot adult and kitten taken by remote camera at the Laguna Atascosa 

National Wildlife Refuge ............................................................................................................... 49

3–4. Photos of buffelgrass, an invasive species that encroaches on native plant habitat............... 56

42

. . . .facing the challenge
vi 

Chapter 4

Challenge Theme 2. Assuring Water Availability and 

Quality in the 21st Century

By James Callegary, Jeff Langman, Jim Leenhouts, and Peter Martin 

Status of Resources .................................................................................................................................. 70

Subarea 1. Pacific Basins and Salton Trough .......................................................................... 74

Subareas 2, 3, and 4. Colorado River and Gulf of California, Mexican Highlands, 

and San Basilio and Mimbres ........................................................................................... 76

Subareas 5, 6, 7, and 8. Rio Grande and Lower Rio Grande Valley—

Elephant Butte Reservoir to the Gulf of Mexico............................................................. 80

Critical Issues............................................................................................................................................. 82

 Capabilities ................................................................................................................................... 86

Estimation of Aquifer Thickness in the Mimbres Groundwater Basin, New Mexico, 

Using Gravity................................................................................................................................. 78

Capture Maps Help Water Managers Understand the Effects of Groundwater Pumping 

on Streams, Springs, and Riparian Vegetation........................................................................ 84

The Use of Semipermeable Membrane Devices To Assess Organic Compounds in the 

Rio Grande from Presidio to Brownsville, Texas..................................................................... 90

Figures

4–1. Map showing comparison of average consumptive use and renewable water 

supply by United States water resources region in the western United States.................. 71

4–2. Map showing watersheds and waterbodies in the eight subareas of the 

United States–Mexican border region ....................................................................................... 72

Tables

4–1. U.S. Geological Survey Water Resources capabilities for examining 

hydrologic systems......................................................................................................................... 88

64

. . . .facing the challenge
 vii

Chapter 5

Challenge Theme 3. Protecting the Environment and 

Safeguarding Human Health

By Diana M. Papoulias and Jean W. Parcher

Introduction ................................................................................................................................................ 92

Issues—Environmental Stressors .......................................................................................................... 94

Agriculture ......................................................................................................................................... 94

Lack of Infrastructure....................................................................................................................... 95

Transportation ................................................................................................................................... 97

Industry .............................................................................................................................................. 98

Energy and Mining............................................................................................................................ 98

Status—Effects of Environmental Stressors ...................................................................................... 102

Air Quality......................................................................................................................................... 102

Water Quality................................................................................................................................... 106

Soil and Sediment Quality ............................................................................................................. 110

Populations at Risk ......................................................................................................................... 110

 Capabilities ................................................................................................................................. 114

Mercury Contamination in Big Bend National Park, Texas .............................................................. 100

Geo-Referenced Database of Contaminants in Biota ....................................................................... 104

Potential Sources of Contaminants in the Lower Rio Grande Valley .............................................. 108

Sediment Cores as a Record of Environmental Contamination along the Rio Grande ................ 112

Figures

5–1. Photo of a colonia dwelling along the United States–Mexican border ................................ 95

5–2. Photos of waste tire piles, a result of increased traffic and trade transportation 

in the United States–Mexican border region ............................................................................ 96

92

. . . .facing the challenge
viii 

Chapter 6

Challenge Theme 4. People in the Borderlands

By Laura M. Norman, Rudy M. Schuster, and Jean W. Parcher

Introduction .............................................................................................................................................. 116

Population Growth................................................................................................................................... 122

Land Use ................................................................................................................................................... 126

Colonias .................................................................................................................................................... 127

Sustainable Development....................................................................................................................... 134

Ecosystem Services ................................................................................................................................ 138

Native American Resources.................................................................................................................. 144

Border Environmental Health Research .............................................................................................. 146

Decision Support Systems ..................................................................................................................... 147

 Capabilities ................................................................................................................................. 152

Binational Land Use and Land Cover Database ................................................................................. 128

CHIPS—A New Way To Monitor Colonia Development along the United States–Mexican 

Border........................................................................................................................................... 132

Binational Planning at Ambos Nogales ............................................................................................... 136

AGAVES—Assessment of Goods and Valuation of Ecosystem Services in the 

San Pedro River Basin, United States and Mexico .............................................................. 142

SCWEPM—The Santa Cruz Watershed Ecosystem Portfolio Model ............................................. 148

Figures

6–1. Photos of colonia dwellings along the United States–Mexican border.............................. 131

116

. . . .facing the challenge
 ix

Chapter 7

Challenge Theme 5. Current and Future Needs of 

Energy and Mineral Resources in the Borderlands 

and the Effects of their Development

By Floyd Gray, William R. Page, Peter D. Warwick, and Martin Valencia-Moreno

Introduction ...............................................................................................................................................154

Porphyry Copper Resources...................................................................................................................156

Other Mineral Deposits and Resources................................................................................................162

Energy Resources.....................................................................................................................................168

Energy and Mineral Resource Issues ...................................................................................................172

 Capabilities ..................................................................................................................................176

Metals Transport from Abandoned Mine Lands, Smelter Emissions, and Metal Solute 

Migration in Groundwater .........................................................................................................160

Acid Mine Drainage in the Patagonia Mountains...............................................................................166

Figures

7–1. Map and comparative charts showing the porphyry copper–rich region of the 

southern United States and northwestern Mexico .................................................................158

7–2. Map showing the distribution of major mines, prospects, and occurrences for 

silver and gold and for copper, lead, and zinc in and adjacent to the 

United States–Mexican border region ......................................................................................164

7–3. Map showing potential energy resources along the United States–Mexican border..........169

7–4. Map showing the Burgos Basin province of northeastern Mexico......................................170

Tables

7–1. Mineral commodities produced in the United States–Mexican border region ..................163

154

. . . .facing the challenge
x 

Chapter 8

Challenge Theme 6. Natural Hazard Risks 

in the Borderlands

By William R. Page, Jean W. Parcher, and Jim Stefanov

Introduction .............................................................................................................................................. 180

Earthquake Hazards ................................................................................................................................ 182

Landslides and Debris Flows ................................................................................................................. 190

Wildfires ................................................................................................................................................... 192

Hurricanes and Floods............................................................................................................................ 196

 Capabilities ................................................................................................................................. 202

2010 El Mayor–Cucapah Earthquake, Baja California, Mexico........................................................ 186

U.S. Geological Survey Support Activities Related to the 2007 Southern California Wildfires....... 194

Vulnerability and Risk Analysis for Sister City Areas along the United States–Mexican Border.. 200

Figures

8–1. Map showing U.S. Geological Survey National Seismic Hazard Map showing 

expected levels of strong earthquake shaking likely to occur within the next 50 years...... 183

8–2. Map showing major active faults along the United States–Mexican border in 

California and Baja California..................................................................................................... 185

8–3. Photo of debris flows in Sabino Canyon in the Santa Catalina Mountains, 

Arizona, caused by record flooding, July 2006 ........................................................................ 190

8–4. Photo of heavy equipment used to clear debris flows in Coronado National 

Memorial, Arizona, July 2006...................................................................................................... 191

8–5. Map showing locations of wildfires in the United States that occurred between 

1980 and 2003 and covered more than 250 acres ................................................................... 192

8–6. Map showing total rainfall for Hurricane Beulah during landfall on the Gulf Coast 

in 1967 with satellite image of the hurricane taken on August 22, 1967.............................. 198

180

. . . .facing the challenge
 xi

Chapter 9

Challenge Theme 7. Information Support for 

Management of Border Security and Environmental 

Protection

By Jean W. Parcher and William R. Page

Introduction .............................................................................................................................................. 204

Border Security and Environmental Protection Issues..................................................................... 206

 Capabilities ................................................................................................................................. 218

United States–Mexico Border Geographic Information System..................................................... 208

U.S. Geological Survey Support in Tunnel Detection Technology................................................... 210

Figures

9–1. Photo of illegal immigrants apprehended near the border ................................................... 207

9–2. Photo of apprehended vehicle loaded with marijuana .......................................................... 207

9–3. Photo of trash left behind by illegal immigrants at Buenos Aires National 

Wildlife Refuge, Arizona.............................................................................................................. 216

9–4. Photo of fence along the United States–Mexican border at Buenos Aires 

National Wildlife Refuge, Arizona.............................................................................................. 217

9–5. Photo of newly constructed fence on the United States–Mexican border near the 

San Diego–Tijuana sister city area (California–Baja California) .......................................... 217

9–6. Map showing Landsat 7 ETM+ multispectral satellite image of the BrownsvilleMatamoros sister city area (Texas-Tamaulipas)..................................................................... 220

9–7. Map showing digital orthophotograph of the Santa Fe Bridge crossing from El Paso, 

Texas, to Ciudad Juárez, Chihuahua.......................................................................................... 221

9–8. Map showing digital elevation model of the area surrounding the Douglas–

Agua Prieta sister city area (Arizona-Sonora) ........................................................................ 222

9–9. Map showing high-resolution LIDAR elevation model of the Brownsville-Matamoros 

sister city area (Texas-Tamaulipas)........................................................................................... 223

9–10. Map showing the different geologic rock types of the Otay Mesa area in the 

California border region north of Baja California.................................................................... 226

9–11. Map showing pilot area for the development of binational watershed boundaries 

and a networked hydrography for the United States–Mexican border region.................. 231

204

. . . .facing the challenge
xii 

Chapter 10

The Borderlands and Climate Change

By Joan Fitzpatrick, Floyd Gray, Russell Dubiel, Jeff Langman, J. Bruce Moring, 

Laura M. Norman, William R. Page, and Jean W. Parcher

Introduction............................................................................................................................................... 234

Climatological Setting of the Borderlands........................................................................................... 236

General Setting................................................................................................................................ 236

Timing and Delivery of Moisture in the Borderlands ................................................................ 240

Important Contributors to Borderlands Climate ........................................................................ 242

North American Monsoon and Tropical Cyclones ........................................................... 242

El Niño–Southern Oscillation Cycle.................................................................................... 244

Pacific Decadal Oscillation Cycle....................................................................................... 246

Projections for Climate Change in the Borderlands .......................................................................... 247

Observed Current Trends............................................................................................................... 247

Global Ensemble Projections and Regional Effects.................................................................. 248

Mesoscale Climate Projections ................................................................................................... 250

Climate and the Borderlands Challenge Themes............................................................................... 252

Challenge Theme 1—Ecological Resources.............................................................................. 252

Challenge Theme 2—Water Availability and Quality................................................................ 254

Challenge Theme 3—Environment and Human Health............................................................ 256

Challenge Theme 4—People in the Borderlands...................................................................... 260

Challenge Theme 5—Energy and Mineral Resources ............................................................. 262

Challenge Theme 6—Natural Hazards ....................................................................................... 264

Challenge Theme 7—Border Security and Environmental Protection.................................. 266

 Capabilities ................................................................................................................................. 268

Multidisciplinary Research ........................................................................................................... 268

Product Development .................................................................................................................... 271

234
 xiii

Figures

10–1. Map showing updated Koppen-Geiger climate classification for the Borderlands .........237

10–2. Map showing annual mean daily average temperature and mean total annual 

precipitation for the conterminous United States for the period 1961–1990 ......................239

10–3. Map showing percentage of yearly precipitation contributed during the warm season 

(mid-June through mid-October), averaged over the period 1958–2003.............................241

10–4. Maps showing projected changes in temperature and precipitation over 

North America from the period 1980–1999 to the period 2080–2099.....................................249

10–5. Map showing satellite image of a dust storm carrying particulates from northern 

Chihuahua into southeastern New Mexico and the Trans-Pecos area of Texas ..............259

10–6. Map showing potential areas for renewable energy development (solar and wind)

in the western United States–Mexican border region...........................................................263

Chapter 11

An Opportunity and an Imperative

By Randall G. Updike and William R. Page

Tables

11–1. Summary of the issues faced in the United States–Mexican border region within

each of the challenge themes used in this report and the strategic goals adopted

by the U.S. Geological Survey to address those issues.........................................................278

Chapter 12

References Cited

Chapter 1 ....................................................................................................................................................................284

Chapter 2 ....................................................................................................................................................................284

Chapter 3 ....................................................................................................................................................................284

Chapter 4 ....................................................................................................................................................................286

Chapter 5 ....................................................................................................................................................................288

Chapter 6 ....................................................................................................................................................................290

Chapter 7 ....................................................................................................................................................................294

Chapter 8 ....................................................................................................................................................................296

Chapter 9 ....................................................................................................................................................................297

Chapter 10 ...................................................................................................................................................................298

Poster

[In back pocket]

272

282
xiv 

Conversion Factors

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 0.4047 hectare (ha)

square mile (mi2

) 2.590 square kilometer (km2) 

Volume

barrel (bbl), (petroleum, 1 barrel=42 gal) 0.1590 cubic meter (m3

) 

gallon (gal) 3.785 liter (L) 

gallon (gal) 0.003785 cubic meter (m3

) 

cubic foot (ft3

) 0.02832 cubic meter (m3) 

acre-foot (acre-ft) 1,233 cubic meter (m3

)

Mass

ton per day (ton/d) 0.9072 metric ton per day

SI to Inch/Pound

Multiply By To obtain

Length

centimeter (cm) 0.3937 inch (in.)

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

hectare (ha) 2.471 acre

square kilometer (km2

) 0.3861 square mile (mi2)

Volume

cubic meter (m3

) 6.290 barrel (petroleum, 1 barrel = 42 gal)

liter (L) 0.2642 gallon (gal)

cubic meter (m3

) 264.2 gallon (gal) 

cubic meter (m3

) 35.31 cubic foot (ft3)

cubic meter (m3

) 0.0008107 acre-foot (acre-ft) 

Mass

metric ton per day 1.102 ton per day (ton/d) 

Temperature in degrees Celsius (°C) may be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8×°C)+32

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

°C=(°F-32)/1.8

1 terawatt (TW) = 103

 gigawatt (GW) = 109 kilowatt (kW)

Vertical coordinate information is referenced to the North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).
 xv

Abbreviations Used in This Report

United States Agencies, Bureaus, Offices, Companies, and Programs

AGAVES Assessment of Goods and Valuation of Ecosystem Services project (USGS)

ASARCO	 formerly American Smelting and Refining Company

BBNP Big Bend National Park (NPS)

BEHI Border Environmental Health Initiative (USGS)

BLM Bureau of Land Management

DOD U.S. Department of Defense

DOI U.S. Department of the Interior

EPA U.S. Environmental Protection Agency

FCC U.S.–Mexico Border Field Coordinating Committee (DOI)

FORT Center Fort Collins Science Center (USGS)

FS U.S. Forest Service (U.S. Department of Agriculture)

FWS U.S. Fish and Wildlife Service

NPS National Park Service

NREL National Renewable Energy Laboratory (U.S. Department of Energy)

NWQL National Water Quality Laboratory (USGS)

SOS	 Office of the Secretary of State of Texas

TAAP Transboundary Aquifer Assessment Program (USGS)

USGS U.S. Geological Survey

Mexican Agencies, Companies, and Programs

BIP Border Industrialization Program (Mexico)

CEMEX formerly Cementos Mexicanos

INEGI Instituto Nacional de Estadística y Geografía) [National Institute of Statistics and Geography]

International Groups and Agreements

IBWC International Boundary and Water Commission

IPCC Intergovernmental Panel on Climate Change

NAFTA North American Free Trade Agreement (1994)

UNESCO	 United Nations Educational, Scientific, and Cultural Organization

Models, Tools, and Datasets

ASTER	 Advanced Spaceborne Thermal Emission and Reflection Radiometer

CHIPS Colonia Health, Infrastructure, and Platting Status tool (USGS)

CVAT Community Vulnerability Assessment Tool (National Oceanic and Atmospheric 

Administration)

HEC-RAS Hydrologic Engineering Center’s River Analysis System (U.S. Army Corp of Engineers)

KINEROS2 kinetic runoff and erosion model (U.S. Department of Agriculture)

LIDAR light detection and ranging

M-SEVI	 Modified Socio-Environmental Vulnerability Index (SCWEPM)

NLCD 1992 National Land Cover Dataset 1992 (USGS)

NLCD 2001 National Land Cover Database 2001 (USGS)

PAGER Prompt Assessment of Global Earthquakes for Response (USGS)

SCWEPM Santa Cruz Watershed Ecosystem Portfolio Model (USGS)

SLEUTH slope, land cover, exclusion, urbanization, transportation, and hillshade urban growth model

SWAT Soil and Water Assessment Tool (SCWEPM)

USMX-GIS United States–Mexico Border Geographic Information System (BEHI)
xvi 

Other

CO2 carbon dioxide

DDE dichlorodiphenyldichloroethylene (daughter product of DDT)

DDT dichlorodiphenyltrichloroethane

DEM digital elevation model

DNA deoxyribonucleic acid

DNI direct normal insulation

ENSO El Niño–Southern Oscillation

FTP	 file transfer protocol

GCM global circulation model

GIS geographic information system

GPS global positioning system

LULC land use and land cover

P-E precipitation minus evaporation

PAH polycyclic aromatic hydrocarbons

PCB polychlorinated biphenyl

PDO	 Pacific Decadal Oscillation

PSOC potential source of contaminants

QRA	 qualified resource area

RCM regional climate model

SB 827 Senate bill 827 (79th Texas Legislature)

SES socioecological systems

SPMD semipermeable membrane device

Units of Measure

acre-ft acre-foot

cm centimeter

ft foot

ft3 cubic foot

gal gallon

ha hectare

in inch

km kilometer

km2 square kilometer

kWh kilowatthour

L liter

m meter

m3 cubic meter

mi mile

mi2 square mile

mm millimeter

s second

TWh terawatthour

yr year
 xvii
borderlands

The United States–Mexican Border—

A Land of Conflict and Opportunity

By Randall G. Updike

The boundary between the United States and Mexico was created 

for convenient expediency through political debate and agreements 

(fig. 1–1). With the exception of the eastern segment of the border, which 

follows the course of the Rio Grande (known as the Rio Bravo in 

Mexico), the defining of this border was based on political decisions 

that had little concern for ecosystems, geologic features, or water—all 

of which span that imaginary line. However, the location of the border 

has had a remarkable effect on the biologic and physical systems in the 

border region and, in turn, has had a growing influence on what we now 

see as 21st century socioeconomic and environmental priorities. Because 

of the complex interactions of the human, ecological, political, and 

economic exigencies associated with this area, the status of the United 

States–Mexican border region, known as the Borderlands,1

 has become 

an ever-present concern for most American citizens and for Mexican and 

United States Federal, State, and local governments.

1

 A note on the terminology in this report—The United States–Mexican border region is alternatively referred 

to as the Borderlands; the term Borderlands has become an accepted name for this region and conveys the 

appropriate degree of inclusiveness for this binational area. Also, because this is a publication of the U.S. Geological 

Survey, American names for features will be used, in accordance with the National Geospatial-Intelligence Agency 

GeoNames database and the USGS Geographic Names Information System. For example, the river forming the 

eastern portion of the border will be referred to as the Rio Grande, though it is known as the Rio Bravo in Mexico, 

and the body of water between Baja California and Sonora will be referred to as the Gulf of California, also known 

as the Sea of Cortez.

Chapter 1
CALIFORNIA

ARIZONA NEW MEXICO

TEXAS

COAHUILA

NUEVO

LEÓN

TAMAULIPAS

BAJA CALIFORNIA

SONORA

CHIHUAHUA PACIFIC OCEAN

Gulf of Mexico

Gulf of California

UNITED STATES 

MEXICO

EXPLANATION

Watershed area—(Woodward and Durall, 1996)

International boundary

Boundary of 1983 La Paz Agreement—100 kilometers from international boundary

COLORADO 

 RIVER

RIO GRANDE

RIO BRAVO

RIO GRANDE

Pecos River

Gila River

115° 110° 105° 100° 95°

30°

35°

25°

El Paso

Ciudad Juárez

Brownsville

Tucson

Tijuana

San Diego

Nuevo Laredo

Nogales

Nogales

Matamoros

Laredo

0 50 100 150 200 KILOMETERS

Base from U.S. Geological Survey 0 50 100 150 200 MILES

GTOPO30 (Global 30 Arc Second Elevation Data)

The United States–Mexican Border—A Land of Conflict and Opportunity 3

Figure 1–1. The immediate area in both countries 

adjacent to the United States–Mexican border, 

known as the Borderlands, has no one set of defining 

boundaries. For example, the boundaries of the 1983 

La Paz Agreement are most appropriate in political 

contexts, but watershed boundaries are more applicable 

to discussions of hydrologic issues. For this report, the 

subareas used to define the Borderlands (see chapter 2) 

are based on watershed boundaries used by the U.S. 

Geological Survey Border Environmental Health Initiative 

(http://borderhealth.cr.usgs.gov). The following chapters 

will provide more precise definitions where needed. 

border region
4 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

San Diego, CALIFORNIA

UNITED STATES

Tijuana, BAJA CALIFORNIA

MEXICO
The United States–Mexican Border—A Land of Conflict and Opportunity 5

As the principal science bureau of the U.S. Department of the Interior (DOI), the U.S. 

Geological Survey (USGS) has a unique role to play in the resolution of a multitude of natural 

and sociological issues in the Borderlands, the area in both countries along the United States–

Mexican border (fig. 1–1). The USGS applies geographical, geospatial, biological, hydrological,

and geological sciences to these complex issues, and the results of that scientific research provide

insight into the area’s natural systems and their relation to human activity. This information is 

useful to Federal land management bureaus in the DOI, such as the Bureau of Land Management, 

and other Federal agencies associated with homeland security, agriculture, environment, and 

health. In addition, as a scientific organization, the USGS has extensive experience in

collecting, analyzing, and making available data that are critical to decisionmakers, and 

perhaps even more importantly, the USGS is an internationally recognized leader in modeling 

natural systems and making robust forecasts of the future states of those systems.

A central challenge for the USGS is that many of the current and future needs for scientific

insight on border issues will require a rigorous multidisciplinary approach that can draw upon 

the expertise of scientists in fields ranging from geography and geology to biology and 

hydrology. For example, modeling future stresses on the natural ecosystems of the lower Rio 

Grande will require studies of the aquatic habitats, hydrologic processes, and geologic 

evolution of the river. The USGS has recognized the need for multidisciplinary science and has 

taken a new, aggressive approach to meet these needs. In 2007, the USGS published Circular 

1309, “Facing Tomorrow’s Challenges—U.S. Geological Survey Science in the Decade 2007–2017,” 

in which this new approach is well elucidated and science themes vital to the USGS—

ecosystems, climate change, energy and minerals, natural hazards, human health, and the water 

census—are discussed from a holistic, multidisciplinary perspective. These multidisciplinary 

science themes that have become the focus of the USGS mission parallel the major challenges 

in the border region between Mexico and the United States. Because of this multidisciplinary 

approach, the USGS possesses a unique set of capabilities that can address these challenges.

U.S. Geological Survey 

employees collecting 

sediment samples in 

response to the 2010 

Deepwater Horizon oil spill

The United States–Mexican Border—A Land of Conflict and Opportunity 7

This circular is intended to provide you—citizen, local decisionmaker, government leader, or private entrepreneur—

an overview of what the USGS considers the current and future challenges in the United States–Mexican border region and 

examples of how the USGS can make a difference in understanding and addressing these issues. The challenges are grouped 

into seven challenge themes: ecological resources, water availability and quality, environment and human health, people in 

the Borderlands, energy and mineral resources, natural hazards, and border security and environmental protection. For each 

of these themes, special “. . . .facing the challenge” sections in the chapters give examples of specific problems addressed or

successes achieved by the USGS. None of these challenge themes can be addressed strictly by one or two science disciplines; 

all require well-integrated, cross-discipline thinking, data collection, and analysis. Because each of the themes is so complex 

and in a constant state of change, there are no easy solutions that can be anticipated for the next few years, but the USGS 

is positioned to provide decisionmakers with the unbiased science necessary to address local and regional problems within 

these challenge themes.
8 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
The United States–Mexican Border—A Land of Conflict and Opportunity 9

Architecture in the pueblo style can be found throughout the 

Borderlands. It is a part of the cultural heritage shared by people 

on both sides of the border.
10 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenges of the Borderlands

The USGS has identified seven challenge themes associated with the Borderlands. Each

theme is explained briefly on pages 12 and 13 and will be discussed more fully in the following

chapters. It is important to keep in mind that these themes are not isolated unto themselves but 

are connected by many pathways and interact with one another to amplify the complexity of 

each theme. Further, it will become evident that the challenges are not one-sided. They do not 

originate in one country only to become problems for the other; the issues and concerns of each 

challenge theme flow in both directions across the border. The clear message is that our two

nations face the issues in these challenge themes together, and the USGS understands it must 

work with its counterparts, partners, and customers in both countries.

President Barack Obama, United States (left), and 

President Felipe Calderón, Mexico (right), January 2009

12 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Ecological Resources (Chapter 3).—Along its corridor from the Gulf of Mexico to the 

Pacific Ocean, the border traverses ecosystems ranging from riparian systems along the Rio

Grande in Texas to the coniferous forest “sky islands” of Arizona and the extremely arid 

regions of southeastern California. Issues associated with biodiversity, invasive species, 

endangered species indicators, habitat fragmentation, and species loss are major components 

of this theme.

Water Availability and Quality (Chapter 4).—Population growth on both sides of the 

border, especially in southern California and Arizona, and pressures for sufficient irrigation

for agriculture in Arizona, California, Texas, and the northern States of Mexico raise enormous 

concerns for future water availability. Even in areas where water remains plentiful, the 

introduction of metals, salts, biochemicals, and pharmaceuticals to surface water and 

groundwater has greatly degraded the qualities of both of these resources.

Environment and Human Health (Chapter 5).—Rapid population growth is occurring 

in the arid southwestern United States and in the northern Mexican States. This theme includes 

the growing health concerns related to the fate of hazardous wastes and contaminants 

introduced into the air, water, and soils of the Borderlands region, as well as pathogens carried 

by wildlife, domesticated animals, and humans.

People in the Borderlands (Chapter 6).—For hundreds of years, the Borderlands have 

been home to small indigenous and immigrant human populations that have had seemingly 

little effect on the expansive landscape. In recent years, however, population centers on both 

sides of the border have grown, leading to intensive agriculture, urban growth, changing land-use 

patterns, expansion of industry, and destruction of cultural resources. This theme is concerned 

with the multidecadal effects of these actions, all of which have escalated significantly in recent

years and are expected to continue to escalate in the foreseeable future.

borderlands challenge themes
The United States–Mexican Border—A Land of Conflict and Opportunity 13

Energy and Mineral Resources (Chapter 7).—The exploration for and exploitation of 

geological resources such as oil and gas, copper, gold, uranium, and mercury have recently 

accelerated as domestic and global demands have increased. This theme focuses on the 

assessment of natural resources and resultant economic development that will occur in the 

Borderlands in the coming decades as a response to an increase in demand, as well as on the 

environmental effects of the extraction of those resources.

Natural Hazards (Chapter 8).—This theme recognizes that the border region is subject 

to rare but spectacular natural events, including hurricanes on both the California–Baja 

California and Texas-Tamaulipas coasts; earthquakes in the San Diego–Tijuana sister city area; 

floods along the Rio Grande in New Mexico, Texas, and Chihuahua; and wildfires in Arizona,

California, Sonora, and Baja California. There is a need for continuous monitoring of earth 

and atmospheric processes that can lead to hazardous events. Populations on both sides of the 

border also need to receive information before a disaster strikes on the steps that can be taken 

to reduce risks associated with these natural hazards.

Border Security and Environmental Protection (Chapter 9).—Because of socioeconomic 

contrasts throughout the Borderlands, problems related to border security, terrorism threats, 

drug and human smuggling, and the degradation of environmental resources are prevalent 

in the area. Management agencies in both the United States and Mexico have been confronted 

with increasingly complicated missions that try to address these issues. This theme focuses 

on providing land management and law enforcement agencies with the information and 

technological support they require but do not necessarily possess internally.

Although it is not listed as a challenge theme, the issue of climate change cannot be 

ignored—the scientific community is now in broad consensus that global climate change is

happening at an accelerating rate. This phenomenon will affect all regions of the United States, 

and the Borderlands are no exception. In fact, the effects of climate change are expected to 

be especially significant in the Borderlands, where even slight climatic fluctuation can have

cascading effects on ecosystems and human inhabitants. Because climate change exerts such 

strong, long-lasting influences on the seven challenge themes in both the United States and

Mexico, the issue of climate change as it applies to the Borderlands will be discussed in depth 

and with a forward-looking perspective (chapter 10).
The Borderlands—

A Region of Physical and Cultural Diversity

By Jean W. Parcher, Diana M. Papoulias, Dennis G. Woodward, 

and Roger A. Durall

The area surrounding the United States–Mexican border is very 

physically and culturally diverse and cannot be generalized by any single 

description. To assist in an accurate appraisal and understanding of this 

remarkable region, the Borderlands team has divided it into eight subareas 

based on the watershed subareas of the U.S. Geological Survey Border 

Environmental Health Initiative (http://borderhealth.cr.usgs.gov) (fig. 2–1), 

the boundaries of which are defined primarily by surface-water drainage 

basins. The drainage basins directly adjacent to or crossing the 

international boundary were automatically included in the defined 

border region, as were those basins that contain unconsolidated aquifers 

that extend to or cross the international boundary. Also, “protected 

areas” adjacent to included basins were selectively added to the defined 

border region. Though some geographic features are entirely within the 

Borderlands, many features—deserts, mountain ranges, rivers, etc.—

extend beyond the region boundaries but are still influential to Borderlands 

environments (fig. 2–2). In some cases, the authors of the following chapters 

have made fine adjustments to the Borderlands boundaries, and they 

have described those alterations where necessary. By describing and 

studying these subareas individually and comparing them to one another, 

we can emphasize the physical and cultural diversity that makes the 

Borderlands such an important geographic area.

Chapter 2
1

2

3 4 5

6

7

8

CALIFORNIA

ARIZONA NEW MEXICO

TEXAS

COAHUILA

NUEVO

LEÓN

TAMAULIPAS

BAJA CALIFORNIA

SONORA

CHIHUAHUA

UNITED STATES 

MEXICO

PACIFIC OCEAN

Gulf of Mexico

Gulf of California

EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

International boundary

1

COLORADO 

 RIVER

RIO GRANDE

RIO BRAVO

RIO GRANDE

Pecos River

Gila River

115° 110° 105° 100° 95°

30°

35°

25°

El Paso

Ciudad Juárez

Brownsville

Tucson

Tijuana

San Diego

Nuevo Laredo

Nogales

Nogales

Matamoros

Laredo

0 50 100 150 200 KILOMETERS

Base from U.S. Geological Survey 0 50 100 150 200 MILES

GTOPO30 (Global 30 Arc Second Elevation Data)

The Borderlands—A Region of Physical and Cultural Diversity 15

borderlands

Figure 2–1. The eight subareas of the United States–Mexican 

border region. The subarea boundaries are based on watershed 

areas used by the U.S. Geological Survey Border Environmental 

Health Initiative. The boundaries were originally defined by 

the U.S. Department of the Interior’s U.S.-Mexico Border Field 

Coordinating Committee (Woodward and Durall, 1996).
Gila River

Salton

Sea

RIO GRANDE

RIO BRAVO

PACIFIC OCEAN

Gulf

of

Mexico

Gulf of California

Santa

San Pedro River

Mimbres River

Cruz

River

Rio Salado

Rio San Rodrigo 

Conchos

Rio

River

Pecos River

Pecos River

Elephant Butte

Reservoir

Amistad

Reservoir

Falcon Reservoir

Devils 

Caballo

Reservoir

Rio Bavispe 

C

O

LORA D

O

RIVER

Lake

Havasu Verde River

RIO

GRANDE

Brazos

River

River

Nueces

Rio San

Rafael 

Rio Sonoyta

Rio 

Rio 

Sonora 

Magdalena

Rio Casas Grandes 

Rio Salinas

Rio Alamo

San Juan 

Rio 

Rio San 

Ferna ndo

Laguna Madre

Laguna Madre

Parker

Dam

Painted

Rock

Dam

Elephant Butte Dam

International Dam

Amistad Dam

Falcon Dam

Arroyo Colorado

TEXAS

CALIFORNIA

ARIZONA

NEW MEXICO

SONORA

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA

Yuma

San Luis

Tucson

Nogales Douglas

Tijuana

San Diego

Agua Prieta Nogales

Los Angeles

Phoenix

Ciudad Juárez

El Paso

Las Cruces

Ojinaga

Hermosillo

Chihuahua

Albuquerque

Laredo

Presidio

Eagle Pass

Brownsville

Ciudad Acuña

Nuevo Laredo

Piedras Negras

Matamoros

Ciudad Victoria

Austin

San Antonio

Corpus Christi

Monterrey

Saltillo

Del Rio

Arizona Upland

Colorado Plateau 

B a s i n a n d R a n g e P r o v i n c e

S i e r r a M a d r e O c c i d e n t a l

S i e r r a M a d r e O r i e n t a l

P e n i n s u l a r R a n g e s

Salton Trough

M o j a v e D e s e r t

Santa Catalina Mtns

C o n t i n e n t a l D i v i d e

R I O G R A N D E R I F T

 West Gulf Coastal Plain

Coastal Plain Province

G r e a t P l a i n s P r o v i n c e

SAN 

ANDREAS TRANSFORM FAULT SYSTEM

Otay

Mesa

Santa Rita

Mtns

S o n o r a n D e s e r t

Lower Colorado

River Valley

Colorado

River

Delta

C h i h u a h u a n D e s e r t

C e n t r a l P l a t e a u

Mexican Highlands

Edwards Plateau

Lower Rio

Grande Valley

Patagonia

Mtns

Madrean Sky Islands

MOGOLLON

DATIL

TRANSITION

ZONE

Pacific Ocean Coastal Plain

110°

35°

30°

100°

105°

115°

25°

0 125 250 KILOMETERS

0 125 250 MILES

Base from U.S. Geological Survey

National Atlas of the United States, 2001,

and Mexico Instituto Nacional de Estadistica,

Geografia, e Informática, 2000, digital data

Albers Conical Equal Area Projection

North American Datum of 1983 (NAD83)

Shaded relief from U.S. Geological Survey

GTOPO30 (Global 30 Arc Second Elevation Data)

MEXICO

UNITED STATES

The Borderlands—A Region of Physical and Cultural Diversity 17

Figure 2–2. Physiographic and geologic features of the United States–Mexican border region.
18 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Cabrillo Point,

San Diego, California

Pacific Basins and Salton Trough

The Pacific Basins–Salton Trough subarea stretches for about 225 kilometers (km)

(140 miles [mi]) along the international boundary from the Pacific Ocean to the Colorado River

and contains basins that drain either to the Pacific Ocean or to enclosed inland seas

(fig. 2–3). Physiographic features include the Pacific Ocean coastal plain, the Peninsular

Ranges of southern California and Baja California, and the Salton Trough, which includes 

the Imperial, Coachella, and Mexicali Valleys south of the Salton Sea (fig. 2–2). The climate

ranges from Mediterranean along the coast to hot and arid in the inland areas. Average annual 

precipitation ranges from about 41 centimeters (cm) (16 inches [in]) in the San Diego–Tijuana 

sister city area (California–Baja California) to about 8 cm (3 in) near the Salton Sea.

With more than 4 million inhabitants, the coastal San Diego–Tijuana sister city area is the 

largest, best educated, and wealthiest population center along the border. The average income 

in both cities is higher than the respective average in each country (Anderson and Gerber, 

2008). Traveling east across the Peninsular Ranges, the desert population areas of the 

Calexico-Mexicali sister cities (California–Baja California) depend on water irrigation rights 

for the Colorado River. Federal lands administered by the U.S. Fish and Wildlife Service 

(FWS), U.S. Forest Service (FS), Bureau of Land Management (BLM), U.S. Department of 

Defense (DOD), and various tribal reservations cover more than one third of the basin. These 

Federal lands include the Tijuana Slough National Wildlife Refuge and National Estuarine 

Research Reserve (FWS and National Oceanic and Atmospheric Administration), Otay 

Mountain Wilderness Area (BLM), Cleveland National Forest (FS), and the Sonny Bono Salton 

Sea National Wildlife Refuge (FWS) (fig. 2–3).

The subareas are discussed in detail in this chapter. We encourage readers to refer back to this 

chapter as they read the following challenge theme chapters; the effects of the phenomena addressed 

by the themes vary according to the physical and cultural characteristics of individual subareas. For 

an overview of physiographic and geologic features, see figure 2–2, and for more detailed data, see the 

tables at the end of this chapter: table 2–1 summarizes information about sister cities and other major 

urban areas and their populations, economic activities, and land use; table 2–2 summarizes information 

about the physiographic provinces, ecoregions, and climate types in the subareas; and table 2–3 

summarizes information about border length, watershed area, major hydrologic features, and elevation 

ranges in the subareas. For more information on climate in the Borderlands, see chapter 10.

Landsat image of

San Diego, California, and 

Tijuana, Baja California

San Diego, CALIFORNIA

UNITED STATES

Tijuana, BAJA CALIFORNIA

MEXICO

Subarea 1.
Approach to the United States–

Mexican border crossing from 

Tijuana, Baja California, to San 

Ysidro, San Diego, California. 

Traffic on the right is moving 

north into the United States.

California coast near

San Diego, California

California brown pelican

(Pelecanus occidentalis 

californicus)
20 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Colorado River and Gulf of California

The Colorado River–Gulf of California subarea extends about 354 km (220 mi) along the international boundary. Basins in 

the subarea include the lower Colorado River watershed below Parker Dam, the lower Gila River watershed below Painted Rock 

Dam, and basins that drain to the Gulf of California (fig. 2–3). This subarea is completely within the Sonoran Desert and encompasses

the lower Colorado River valley, the Colorado River delta, and the Arizona Upland (fig. 2–2). The majority of the lower Colorado

River valley is sandy or gravely plains, but it also contains low mountains, sand dunes, and alkali sinks.

The major population centers of the Yuma–San Luis sister city area (Arizona-Sonora) rely on agriculture, manufacturing, 

and tourism for their economic base. The majority of Federal and tribal lands on the United States side of the border are 

administered by the FWS, FS, BLM, DOD, and the Tohono O’odham Nation. Within Mexico, the Reserva de la Biosfera Alto 

Golfo de California y Delta del Rio Colorado [biosphere reserve] is one of the largest ecosystem reserves in the world (Rapport 

and others, 2002) (fig. 2–3).

Figure 2–3 (facing page). Locations of the Pacific Basins–Salton 

Trough subarea (1) and the Colorado River–Gulf of California 

subarea (2), with United States and Mexican agency land holdings 

and protected areas.

Subarea 2.
CALIFORNIA

ARIZONA

SONORA

BAJA 

CALIFORNIA

UNITED STATES

MEXICO

1

2

Yuma

Tucson

Nogales

Tijuana

Ensenada

Calexico

El Centro

Tecate

Mexicali

San Diego

Nogales

 San Luis

Cananea

Puerto Peñasco

Los Angeles

Phoenix

RESERVA

DE LA BIOSFERA

ALTO GOLFO

DE CALIFORNIA

Y DELTA DEL RIO

COLORADO

CIBOLA

NATIONAL

WILDLIFE

REFUGE

SONNY BONO

SALTON SEA

NATIONAL WILDLIFE

REFUGE

OREGON PIPE CACTUS

NATIONAL

MONUMENT

CABEZA PRIETA NATIONAL WILDLIFE REFUGE TOHONO

O’ODHAM

NATION

CLEVELAND

NATIONAL

FOREST

OTAY

MOUNTAIN

WILDERNESS

AREA

TIJUANA SLOUGH NATIONAL WILDLIFE REFUGE

AND NATIONAL ESTUARINE RESEARCH RESERVE

PACIFIC OCEAN

Gulf of California

Verde River

Santa Cruz River

Rio 

Rio 

San Pedro River

Parker

Dam

Sonoyta

Magdalena

Gila River

Rio San Rafael 

Painted Rock Dam

Salton Sea

Lake

Havasu

C

O

LORAD O

RIVER

115°

30°

35°

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

1

2

EXPLANATION

Federal lands in the United States

Indian reservation lands in the United States

Bureau of Land Management

Bureau of Reclamation

Department of Defense

Forest Service

Fish and Wildlife Service

National Park Service

Protected areas in Mexico 

International boundary

Área de Protección de Flora y Fauna

Parque Nacional

Reserva de la Biosfera

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

1

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

Shaded relief base from U.S. Geological Survey GTOPO30 

(Global 30 Arc Second Elevation Data), accessed June 2010 at

http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30_info

Albers Conical Equal Area Projection

North American Datum of 1983 (NAD83)

U.S. river and Federal lands data from the National Atlas of the United States, 

accessed June 2010 at http://nationalatlas.gov

Mexico data from Comisión Nacional de Áreas Naturales Protegidas, 

accessed June 2010 at http://sig.conanp.gob.mx/website/anpsig/viewer.htm

The Borderlands—A Region of Physical and Cultural Diversity 21
Mexican Highlands

The Mexican Highlands subarea, which is part of the Basin and Range physiographic province, extends about 274 km (170 mi) 

along the international border and is characterized by broad valleys or basins separated by steeply rising mountain ranges 

(figs. 2–2 and 2–4). Each basin is essentially an independent hydrologic system. The subarea contains basins that drain to rivers

in southern Arizona, southwestern New Mexico, northern Sonora, and the northwestern tip of Chihuahua (Papoulias and others, 

1997). The Mexican Highlands subarea is classified as desert. This desert area is noteworthy for its lush vegetation and diverse

aquatic habitats, which are remnants from a time when the climate was wetter.

The Arizona Upland (fig. 2–2) is located mostly in south-central Arizona and has more mountain ranges than other areas

in the Sonoran Desert. The climate is subtropical desert with two distinct periods of precipitation: winter frontal storms produce 

periods of extensive, low-intensity rain, and the summer monsoon’s intense convective storms produce locally heavy 

precipitation when moisture-rich air masses originating in the Gulf of Mexico move across the area. The twice-yearly pattern 

of rainfall, coupled with the variety of landscape and soil types, have led to varied habitats which support some 2,500 species 

of plants and animals (Phillips and Wentworth-Comus, 1999).

More than a third of the subarea is covered by the Tohono O’odham Indian Reservation (fig. 2–4), extending into the

northwest corner of the subarea, and U.S. Federal lands, including various national forests and BLM holdings. Major population 

centers include Tucson, Ariz., with the second highest per capita income in the Borderlands behind San Diego, Calif.; the sister city 

area of Nogales-Nogales (Arizona-Sonora); and the former copper mining sister city area of Douglas–Agua Prieta (Arizona-Sonora) 

(Anderson and Gerber, 2008).

United States–Mexican 

border fence between 

Nogales, Arizona (left), 

and Nogales, Sonora (right)

Bisbee, Arizona

Subarea 3.
View to the east along the 

United States–Mexican border, 

with Nogales, Arizona, to the 

left, and Nogales, Sonora, to the 

right, 2007

View to the west of Nogales 

along International Street, with 

Arizona to the right and Sonora then to the left, ca. 1899

now
24 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Columbus, New Mexico

Figure 2–4 (facing page). Locations of the Mexican Highlands 

subarea (3) and the San Basilio–Mimbres subarea (4), with United 

States and Mexican agency land holdings and protected areas.

San Basilio and Mimbres

The San Basilio–Mimbres subarea is an interconnected group of hydrologic subbasins that 

extend about 225 km (140 mi) along the United States–Mexican international boundary where 

New Mexico borders Chihuahua (fig. 2–4). Most of the subarea is located in the Mexican

Highlands section of the Basin and Range physiographic province (fig. 2–2). This subarea is

one of the most sparsely populated areas along the border, characterized in the south by the 

rocky and dry landscape of the Chihuahuan Desert and extending northward into the MogollonDatil transition zone (fig. 2–2). The climate is characterized by hot summers and mild winters

with nearly half of the rain falling during the monsoon season from July through September.

Small agricultural communities, such as Playas, Antelope Wells, Hachita, Deming, 

Columbus, White Signal, Hurley, and Silver City in New Mexico and El Berrendo and Las 

Palomas in Chihuahua, provide market centers for the farms and rural residents. The BLM 

manages several recreational areas near the United States–Mexican border.

Herd of pronghorn (Antilocapra americana)

Subarea 4.
ARIZONA

NEW MEXICO

SONORA

CHIHUAHUA

UNITED STATES

MEXICO

3 4

Tucson

Bisbee Douglas

Sierra Vista

Nogales

Agua Prieta

Nogales

Cananea

Phoenix

Las Cruces

Deming

Silver City Mimbres

Hurley

White

Signal

Hachita

Playas

Columbus

Las Palomas

Antelope Wells

El Berrendo

San

Basilio

Verde River

Santa Cruz River

Rio 

Rio Casas Grandes 

Rio Sonora 

San Pedro River

Rio Bavispe

Elephant Butte

 Reservoir

Caballo

 Reservoir

Magdalena

Elephant Butte

Dam

Mimbres

River

110°

30°

BUENOS AIRES NATIONAL WILDLIFE REFUGE

CORONADO

NATIONAL

FOREST

(CNF)

SAN PEDRO

RIPARIAN

NATIONAL

CONSERVATION

AREA

CORONADO

NATIONAL

MEMORIAL

SAGUARO

NATIONAL

PARK

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

(CNF)

TOHONO

O’ODHAM

NATION

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

3 4

EXPLANATION

Indian reservation lands in the United States

Federal lands in the United States

Bureau of Land Management

Bureau of Reclamation

Department of Defense

Forest Service

Fish and Wildlife Service

National Park Service

Other Federal lands

Protected areas in Mexico 

Área de Protección de Flora y Fauna

Subareas of the border region

3 Mexican Highlands

4 San Basilio–Mimbres

3

International boundary

Shaded relief base from U.S. Geological Survey GTOPO30 

(Global 30 Arc Second Elevation Data), accessed June 2010 at

http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30_info

Albers Conical Equal Area Projection

North American Datum of 1983 (NAD83)

U.S. river and Federal lands data from the National Atlas of the United States, 

accessed June 2010 at http://nationalatlas.gov

Mexico data from Comisión Nacional de Áreas Naturales Protegidas, 

accessed June 2010 at http://sig.conanp.gob.mx/website/anpsig/viewer.htm

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

The Borderlands—A Region of Physical and Cultural Diversity 25
26 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Rio Grande West—

Elephant Butte Reservoir to Rio Conchos

The Rio Grande West subarea extending from Elephant Butte Reservoir to the Rio 

Conchos is an interconnected group of hydrologic basins in the Rio Grande Rift (an eastern 

segment of the Basin and Range physiographic province) that drain to the Rio Grande between 

Elephant Butte Dam and the Rio Conchos confluence (fig. 2–2). The area extends about 515 km

(320 mi) along the international boundary between New Mexico and Texas to the northeast and 

Chihuahua to the southwest. The riparian banks of the Rio Grande support irrigated desert 

agriculture from Las Cruces, N. Mex., to south of the El Paso–Ciudad Juárez sister city area. 

Elevations range from about 610 to 1,676 meters (m) (2,000 to 5,500 feet [ft]). Climate is 

characterized by hot summers and cool winters, and annual precipitation generally is less than 

15 cm (6 in).

Major Federal land holdings include the Elephant Butte and Caballo Reservoirs (Bureau 

of Reclamation), the White Sands National Monument (National Park Service [NPS]), the 

Chamizal National Memorial in El Paso (NPS), the Guadalupe Mountains National Park and 

Wilderness Area (NPS), the San Andres National Wildlife Refuge (FWS), and several BLM 

holdings (fig. 2–5).

The El Paso–Ciudad Juárez sister city area is the second largest population center along 

the United States–Mexican border. With five major border crossings and significant

manufacturing and commercial centers, this binational metropolitan area is closely linked 

economically, politically, and socially. Scarcity of water is a limiting factor for growth in the 

area. The area southeast of El Paso and Ciudad Juárez is sparsely populated and lacks roads and 

border crossings until the junction of the Rio Conchos with the Rio Grande near the sister city 

area of Presidio-Ojinaga (Texas-Chihuahua) at the border with the Rio Grande Central subarea.

Presidio Chapel of San Elizario, 

El Paso, Texas

Portico at the Presidio Chapel 

of San Elizario, El Paso, Texas

Door at the Socorro Mission,

El Paso, Texas

Subarea 5.
The Borderlands—A Region of Physical and Cultural Diversity 27

Cathedral of Ciudad Juárez (right) and the 

17th century Mission of Our Lady of Guadelupe (left), 

Ciudad Juárez, Chihuahua, 2007

Mission of Our Lady of Guadelupe in the late 19th century, 

Ciudad Juárez, Chihuahua

then

now
28 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
White Sands National Monument, New Mexico, is one of many 

federally protected areas in the Rio Grande West subarea.

The Borderlands—A Region of Physical and Cultural Diversity 29
30 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Rio Grande Central—

Rio Conchos to Amistad Reservoir

The Rio Grande Central subarea from the Rio Conchos to Amistad Reservoir extends 

about 636 km (395 mi) along the Rio Grande international border (fig. 2–5). This sparsely

populated subarea is in the Chihuahuan Desert and the Rio Grande Rift (fig. 2–2). The isolated

mountain ranges separated by desert basins in Big Bend National Park near the center of the 

subarea are characteristic of the southern Rio Grande Rift and the northern Chihuahuan Desert. 

The Rio Grande flows through deep, steep-walled canyons of limestone, forming a ribbon-like

oasis of riverine and riparian environments that are a stark contrast to the adjacent desert 

landscape. Contributing tributaries include the Rio Conchos, Pecos River, and Devils River. 

The latter two contribute flow directly to Amistad Reservoir, which is a binational reservoir

shared between Mexico and the United States that was created to control the downstream 

flooding of homes and farms. The Rio Conchos watershed in its entirety contains almost one

half of the entire Rio Grande drainage area in Mexico.

Protected areas can be found on both sides of the international border. The Reserva de la 

Biosfera Maderas del Carmen [biosphere reserve] and the Área de Protección de Flora y Fauna 

Cañón de Santa Elena [protected flora and fauna area] in Mexico cover nearly 485,640 hectares (ha)

(1.2 million acres) (fig. 2–5). In the United States, the NPS manages Big Bend National Park,

the Rio Grande Wild and Scenic River (within and to the east of Big Bend National Park), 

and the Amistad National Recreation Area at Amistad Reservoir, all in Texas (Blackstun and 

others, 1998).

There are no major population centers. Along the banks of the Rio Grande just north of 

Big Bend National Park, the once-thriving mining towns of Lajitas and Terlingua, Tex., 

currently lack official border crossings.

Sierra del Carmen, Texas

Pecos River, Texas

Subarea 6.
Cave art at Amistad Reservoir, 

Texas
TEXAS

NEW MEXICO

CHIHUAHUA

COAHUILA

NUEVO 

LEÓN

UNITED STATES

MEXICO

5

6

Ciudad

Juárez

El Paso

Las Cruces

Ojinaga

Chihuahua

Deming

Silver City

Hurley

Columbus

Las Palomas

Albuquerque

Carlsbad

Presidio

Fort Quitman

Eagle Pass

Ciudad Acuña

Piedras Negras

Terlingua

Lajitas Del Rio

 Pecos River

Rio 

Casas

 Grandes 

Rio Conchos 

Rio Salado 

Rio San Rodrigo

River

Devils

Amistad Reservoir

Amistad Dam

Elephant Butte

 Reservoir

Caballo

 Reservoir

RIO

GRANDE

RIO 

Pecos River

GRANDE

RIO BRAVO

Elephant Butte

Dam

International

Dam

105° 100°

35°

30°

RESERVA

DE LA BIOSFERA MADERAS

DEL CARMEN

BIG BEND

NATIONAL

PARK

GUADALUPE

MOUNTAINS

NATIONAL PARK AND

WILDERNESS AREA

SAN ANDRES

NATIONAL WILDLIFE REFUGE

WHITE SANDS

NATIONAL

MONUMENT

FORT

BLISS

ÁREA

DE PROTECCIÓN

DE FLORA Y FAUNA

CAÑÓN DE

SANTA ELENA

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

Shaded relief base from U.S. Geological Survey GTOPO30 

(Global 30 Arc Second Elevation Data), accessed June 2010 at

http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30_info

Albers Conical Equal Area Projection

North American Datum of 1983 (NAD83)

U.S. river and Federal lands data from the National Atlas of the United States, 

accessed June 2010 at http://nationalatlas.gov

Mexico data from Comisión Nacional de Áreas Naturales Protegidas, 

accessed June 2010 at http://sig.conanp.gob.mx/website/anpsig/viewer.htm

32 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

5

6

EXPLANATION

Indian reservation lands in the United States

Federal lands in the United States

Bureau of Land Management

Bureau of Reclamation

Department of Defense

Forest Service

Fish and Wildlife Service

National Park Service

Protected areas in Mexico 

Área de Protección de Flora y Fauna

Parque Nacional

Reserva de la Biosfera

Áreas de Protección de Recursos Naturales

Subareas of the border region

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

5

International boundary

The Borderlands—A Region of Physical and Cultural Diversity 33

Figure 2–5 (facing page). Locations of the Rio Grande West 

subarea (5), from Elephant Butte Reservoir to the Rio Conchos, 

and the Rio Grande Central subarea (6), from the Rio Conchos to 

Amistad Reservoir, with United States and Mexican agency land 

holdings and protected areas.

Santa Elena Canyon, Big Bend National Park, Texas

Cretaceous fossil at Big Bend National Park, Texas
34 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Rio Grande East—

Below Amistad Reservoir to Falcon Reservoir

The Rio Grande East subarea from below Amistad Reservoir to Falcon Reservoir is an 

interconnected group of hydrologic basins that drain either to the Rio Grande or to the lower 

reach of the Rio Salado (fig. 2–6). The area extends about 483 km (300 mi) along the

international boundary between Texas in the United States and Coahuila, Nuevo León, and 

Tamaulipas in Mexico. The northernmost section of the subarea is located in the Edwards 

Plateau, Tex. (fig. 2–2), an area underlain by massive limestone deeply cut by arroyos and

canyons. Most of the subarea south of Eagle Pass, Tex., is in the Rio Grande floodplain.

Elevations range from about 96 m (314 ft) at the international Falcon Reservoir, managed by 

the International Boundary and Water Commission (IBWC), to 891.5 m (2,925 ft) in Val Verde 

County, Tex. The climate is subtropical to subhumid with average annual precipitation of 

43–48 cm (17–19 in). Drought periods with annual precipitation of less than 15 cm (6 in) are 

not uncommon.

Federal lands in this area, including Falcon Reservoir and the right-of-way along the 

Rio Grande, are all managed by the IBWC. The principal sister city population centers of 

Del Rio–Ciudad Acuña (Texas-Coahuila), Eagle Pass–Piedras Negras (Texas-Coahuila), and 

Laredo–Nuevo Laredo (Texas-Tamaulipas) are connected economically and socially, with each 

Mexican sister city having at least double the population of its United States sister city. The 

entry ports of the Laredo–Nuevo Laredo area are strategically located near the industrial city 

of Monterrey, Nuevo León. The Laredo port of entry supports more than 50 percent of all truck 

crossings through Texas and is the largest inland port in the United States (Anderson 

and Gerber, 2008).

Founder’s Monument, Nuevo Laredo, Tamaulipas

Subarea 7.
The Borderlands—A Region of Physical and Cultural Diversity 35

Lake Casa Blanca State Park, Laredo, Texas
36 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Figure 2–6 (facing page). Locations of the Rio Grande East 

subarea (7), from below Amistad Reservoir to Falcon Reservoir, 

and the Lower Rio Grande Valley subarea (8), with United States 

and Mexican agency land holdings and protected areas.

Lower Rio Grande Valley

The Lower Rio Grande Valley subarea is physiographically characterized as the West Gulf 

Coastal Plain (fig. 2–2) (U.S. Geological Survey, 2003). The subarea contains basins that drain

to either the Rio Grande, the lower reaches of the Rio San Juan, or the Arroyo Colorado in 

southern Texas (fig. 2–6). This subarea extends about 451 km (280 mi) along the international

border between Texas in the United States and Tamaulipas and Nuevo León in Mexico, 

terminating in the wetlands and marshes of the Gulf of Mexico and the Laguna Madre of 

Texas and Tamaulipas (Buckler and others, 2002). The landscape is characterized by a wide 

deltaic floodplain, interspersed with abandoned river channel meanders, which are locally

referred to as resacas.

Native Tamaulipan brushland characterized by dense, woody, and thorny vegetation and 

a high degree of biological diversity is the dominant land cover. This taller and more lush 

vegetation in riparian areas not only provides important nesting and feeding habitat, but also 

serves as corridors for animal movement. The subtropical humid climate, with an average 

annual rainfall of about 66 cm (26 in) at the mouth of the Rio Grande and about 41 cm (16 in) 

at Falcon Dam, is strongly influenced by weather activity related to the Gulf of Mexico.

Federally owned or managed areas include the Santa Ana and Lower Rio Grande Valley 

National Wildlife Refuges along the Rio Grande in McAllen, Tex. (FWS), the Laguna 

Atascosa National Wildlife Refuge (FWS), and the Palo Alto Battlefield National Historic Site

in Brownsville, Tex. (NPS) (fig. 2–6). The major metropolitan areas of McAllen, Harlingen,

and Brownsville in Texas and Reynosa and Matamoros in Tamaulipas support more than a 

million habitants through tourism, manufacturing, and agriculture. As in other border subareas, 

the water resources and associated plant, fish, and wildlife communities of the Lower Rio

Grande Valley subarea are increasingly subject to the pressures of human activities.

References cited in this chapter are listed in chapter 12.

South Padre Island, Texas

Rio Grande at Roma, Texas

Hand-powered ferry on the 

Rio Grande at the United States–

Mexican border crossing 

between Los Ebanos, Texas, and 

Gustavo Díaz Ordaz, Tamaulipas

Subarea 8.
TEXAS

TAMAULIPAS

COAHUILA

NUEVO 

LEÓN

UNITED STATES

MEXICO

7

8

Laredo

McAllen

Reynosa

Eagle Pass

Brownsville

Ciudad Acuña

Nuevo Laredo

Piedras Negras

Matamoros

Harlingen

Austin

San Antonio

Monterrey

Saltillo

Del Rio

Gulf

of

Mexico

Rio Salado 

Rio San Rodrigo

Las Moras

Creek

Rio Salinas

Nueces River

San Juan 

Devils River

Amistad Reservoir

Amistad Dam

Falcon Reservoir

Brazos River

Rio San Fernando

Rio 

Arroyo Colorado

Laguna Madre

Laguna Madre

RIO GRANDE

RIO BRAVO

Falcon Dam

Padre Island

100°

30°

25°

LAGUNA

ATASCOSA

NATIONAL

WILDLIFE

REFUGE

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

7

8

Shaded relief base from U.S. Geological Survey GTOPO30 

(Global 30 Arc Second Elevation Data), accessed June 2010 at

http://eros.usgs.gov/#/Find_Data/Products_and_Data_Available/gtopo30_info

Albers Conical Equal Area Projection

North American Datum of 1983 (NAD83)

U.S. river and Federal lands data from the National Atlas of the United States, 

accessed June 2010 at http://nationalatlas.gov

Mexico data from Comisión Nacional de Áreas Naturales Protegidas, 

accessed June 2010 at http://sig.conanp.gob.mx/website/anpsig/viewer.htm

EXPLANATION

Federal lands in the United States

Bureau of Reclamation

Department of Defense

Fish and Wildlife Service

National Park Service

Protected areas in Mexico 

International boundary

Área de Protección de Flora y Fauna

Parque Nacional

Área de Protección de Recursos Naturales

Monumento Natural

Subareas of the border region

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

7

0 25 50 75 100 KILOMETERS

0 25 50 75 100 MILES

The Borderlands—A Region of Physical and Cultural Diversity 37
38 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Table 2–1. Information on sister cities, major urban areas, and population; economic activities; and land use for the eight subareas of 

the United States–Mexican border region.

[ha, hectare]

Sister cities and

major urban areas Population Economic activities Major land use

1 Pacific Basins–Salton Trough

San Diego, California

Tijuana, Baja California

Calexico, California

Mexicali, Baja California

1,256,951

1,483,992

37,243

855,962

Biotechnology, wireless communication, digital 

media, defense industries, manufacturing, 

tourism, agriculture, food processing

Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

8,880 ha (21,941 acres)

8,178 ha (20,208 acres)

68,094 ha (168,258 acres)

4,520 ha (11,169 acres)

8,812 ha (21,774 acres)

410 ha (1,012 acres)

2 Colorado River–Gulf of California

Yuma, Arizona

San Luis, Sonora

87,423

157,076

Agriculture, manufacturing, tourism, military Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

1,885 ha (4,658 acres)

9,284 ha (22,941 acres)

161,519 ha (399,107 acres)

269 ha (665 acres)

4,623 ha (11,423 acres)

3,085 ha (7,624 acres)

3 Mexican Highlands

Nogales, Arizona

Nogales, Sonora

Douglas, Arizona

Agua Prieta, Sonora

Tucson, Arizona

20,878

193,517

14,312

70,303

518,956

Mining, agriculture, manufacturing–maquiladoras1 Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

3,819 ha (9,437 acres)

3,503 ha (8,657 acres)

146,143 ha (361,115 acres)

13,473 ha (33,292 acres)

19,058 ha (47,092 acres)

224 ha (553 acres)

4 San Basilio–Mimbres

Columbus, New Mexico

Las Palomas, Chihuahua

1,765

5,748

Agriculture Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

848 ha (2,096 acres)

4,196 ha (10,367 acres)

72,706 ha (179,653 acres)

6,499 ha (16,060 acres)

22,633 ha (55,925 acres)

42 ha (104 acres)

5 Rio Grande West: Elephant Butte Reservoir to Rio Conchos

El Paso, Texas

Ciudad Juárez, Chihuahua 

Las Cruces, New Mexico

609,415

1,313,338

86,268

Manufacturing, commercial, agriculture, military Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

3,774 ha (9,325 acres)

4,231 ha (10,454 acres)

201,444 ha (497,762 acres)

10,508 ha (25,966 acres)

22,789 ha (56,311 acres)

202 ha (500 acres)

6 Rio Grande Central: Rio Conchos to Amistad Reservoir

Presidio, Texas

Ojinaga, Chihuahua

4,167

21,157

Tourism, mining, agriculture Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

1,107 ha (2,735 acres)

798 ha (1,973 acres)

271,511 ha (670,894 acres)

3,900 ha (9,637 acres)

16,706 ha (41,279 acres)

306 ha (757 acres)

7 Rio Grande East: below Amistad Reservoir to Falcon Reservoir

Del Rio, Texas

Ciudad Acuña, Coahuila 

Eagle Pass, Texas

Piedras Negras, Coahuila

Laredo, Texas

Nuevo Laredo, Tamaulipas

36,491

126,238

22,413

169,771

215,484

355,827

Agriculture, mining, tourism Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

2,811 ha (6,945 acres)

4,618 ha (11,410 acres)

77,620 ha (191,797 acres)

1,352 ha (3,341 acres)

23,174 ha (57,262 acres)

716 ha (1,769 acres)

8 Lower Rio Grande Valley

McAllen, Texas

Reynosa, Tamaulipas

Brownsville, Texas

Matamoros, Tamaulipas 

Harlingen, Texas

146,411

633,730

172,437

462,157

64,202

Tourism, manufacturing, agriculture Urban

Agriculture

Shrubland

Forest

Grassland

Wetland

5,175 ha (12,788 acres)

29,709 ha (73,409 acres)

22,012 ha (54,390 acres)

463 ha (1,144 acres)

22,158 ha (54,752 acres)

4,345 ha (10,737 acres)

1

Maquiladoras are foreign-owned manufacturing and assembly plants along the Mexican side of the border. See chapters 5 and 6 for more information.
The Borderlands—A Region of Physical and Cultural Diversity 39

Table 2–2. Physiographic provinces, ecoregions, and climate types included in the eight subareas of the United States–Mexican 

border region. See figure 2–2 for more on physiographic and geologic features and figure 3–1 for more on ecoregions.

Physiographic provinces,

sections, and other features Ecoregions Climate types

1 Pacific Basins–Salton Trough

Coastal Plain province, Peninsular 

Ranges, Salton Trough

California Coastal Sage, Chaparral, and Oak Woodlands; 

Sonoran Desert

Coastal Mediterranean; 

Inland desert

2 Colorado River–Gulf of California

Sonoran Desert, Colorado River valley, 

Colorado River delta, Arizona Upland

Sonoran Desert Subtropical desert (summer 

and winter rains)

3 Mexican Highlands

Broad valleys and steep mountains Sonoran Desert; Madrean Archipelago; Chihuahuan Desert Arid

4 San Basilio–Mimbres

Continental Divide, Rio Grande rift zone Chihuahuan Desert Arid

5 Rio Grande West: Elephant Butte Reservoir to Rio Conchos

Basin and Range province, Chihuahuan 

Desert, Franklin Mountains

Chihuahuan Desert Arid 

6 Rio Grande Central: Rio Conchos to Amistad Reservoir

Basin and Range province, Great Plains 

province

Chihuahuan Desert Arid

7 Rio Grande East: below Amistad Reservoir to Falcon Reservoir

Edwards Plateau Southern Texas Plains/Interior Plains and Hills with Xerophytic 

Shrub and Oak Forest

Subtropical

8 Lower Rio Grande Valley

Gulf Coastal Plain Southern Texas Plains/Interior Plains and Hills with Xerophytic 

Shrub and Oak Forest; Western Gulf Coastal Plain

Subtropical

1 2

3 4 5

6

7

8

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

International boundary

1
40 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Table 2–3. Border length, watershed area, major hydrologic features, and elevation ranges for the eight subareas of the United 

States–Mexican border region. See figure 4–2 for more on watersheds and hydrologic features.

[km, kilometer; mi, mile; km 2, square kilometer; mi2, square mile; m, meter; ft, foot]

Border length Watershed area Major hydrologic features Elevation range 

(above sea level)

1 Pacific Basins–Salton Trough

225 km (140 mi) 36,260 km2

 (14,000 mi2)

Mexico: 12,613 km2

 (4,870 mi2)

United States: 23,647 km2

 (9,130 mi2)

Pacific Ocean, Salton Sea Sea level to 3,048 m (10,000 ft)

2 Colorado River–Gulf of California

354 km (220 mi) 58,508 km2

 (22,590 mi2)

Mexico: 21,678 km2

 (8,370 mi2)

United States: 36,830 km2

 (14,220 mi2)

Colorado River, Gulf of California Sea level to 1,067 m (3,500 ft)

3 Mexican Highlands

274 km (170 mi) 56,566 km2

 (21,840 mi2)

Mexico: 13,973 km2

 (5,395 mi2)

United States: 42,593 km2

 (16,445 mi2)

Santa Cruz River, San Pedro River 549–2,743 m (1,800–9,000 ft)

4 San Basilio–Mimbres

225 km (140 mi) 32,245 km2

 (12,450 mi2)

Mexico: 16,019 km2

 (6,185 mi2)

United States: 16,226 km2

 (6,265 mi2)

Mimbres River, Rio Casas Grandes 1,189–3,094 m (3,900–10,150 ft)

5 Rio Grande West: Elephant Butte Reservoir to Rio Conchos

515 km (320 mi) 74,954 km2

 (28,940 mi2)

Mexico: 14,918 km2

 (5,760 mi2)

United States: 60,036 km2

 (23,180 mi2)

Rio Grande, Elephant Butte 

Reservoir, Caballo Reservoir

762–3,200 m (2,500–10,500 ft)

6 Rio Grande Central: Rio Conchos to Amistad Reservoir

636 km (395 mi) 89,692 km2

 (34,630 mi2)

Mexico: 36,027 km2

 (13,910 mi2)

United States: 53,665 km2

 (20,720 mi2)

Rio Grande, Amistad Reservoir, 

Rio Conchos, Pecos River, 

Devils River

351–2,377 m (1,150–7,800 ft)

7 Rio Grande East: below Amistad Reservoir to Falcon Reservoir

483 km (300 mi) 33,437 km2

 (12,910 mi2)

Mexico: 20,306 km2

 (7,840 mi2)

United States: 13,131 km2

 (5,070 mi2)

Rio Grande, Falcon Reservoir, 

Las Moras Creek, Rio Salado, 

Rio Salinas

91–1,311 m (300–4,300 ft)

8 Lower Rio Grande Valley

451 km (280 mi) 26,522 km2

 (10,240 mi2)

Mexico: 15,942 km2

 (6,155 mi2)

United States: 10,580 km2

 (4,085 mi2)

Rio Grande, Rio San Juan, 

Laguna Madre, Gulf of Mexico

Sea level to 1,250 m (4,100 ft)
The Borderlands—A Region of Physical and Cultural Diversity 41
42 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 1. Understanding and 

Preserving Ecological Resources

By J. Bruce Moring, Diana M. Papoulias, and Charles van Riper III

Background 

The notable biodiversity within the United States–Mexican border 

region is driven by the wide variety of natural landscapes in the area and 

its biologically unique transition zone of habitats for xeric, temperate, and 

subtropical species. Six diverse ecoregions cover the length of the border 

(fig. 3–1): California Coastal Sage, Chaparral, and Oak Woodlands; 

Sonoran Desert; Madrean Archipelago; Chihuahuan Desert; Southern 

Texas Plains; and Western Gulf Coastal Plain.

The unique geology and many of the distinctive geographic features 

and climatic conditions that have given rise to the diverse populations of 

plants and animals found in the Borderlands also attract human populations. 

The number of people living in the Borderlands has increased dramatically 

over recent years, from about 7 million in 1980 to almost 12 million in 

2003; the population is estimated to be more than 18 million by 2020 

(Peach and Williams, 2003). The human population increase and associated 

change in land use have contributed to habitat fragmentation and habitat 

loss for native species, thus threatening their survival. Some ways in 

which humans negatively affect plants and animals in the Borderlands 

include dewatering of aquatic ecosystems, water pollution, introduction 

and spread of invasive species, outdoor lighting, military and border 

enforcement activity, and energy development and transmission.

Chapter 3
1

2

3 4 5

6

7

8

CALIFORNIA

ARIZONA NEW MEXICO

TEXAS

COAHUILA

NUEVO

LEÓN

TAMAULIPAS

BAJA CALIFORNIA

SONORA

CHIHUAHUA

UNITED STATES 

MEXICO

PACIFIC OCEAN

Gulf of Mexico

Gulf of California

EXPLANATION

Ecological Regions

California Coastal Sage, Chaparral, and Oak Woodlands

Sonoran Desert

Madrean Archipelago

Chihuahuan Desert

Southern Texas Plains/Interior Plains and Hills

 with Xerophytic Shrub and Oak Forest

Western Gulf Coastal Plain

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

International boundary

1

COLORADO 

 RIVER

RIO GRANDE

RIO BRAVO

RIO GRANDE

Pecos River

Gila River

115° 110° 105° 100° 95°

30°

35°

25°

El Paso

Ciudad Juárez

Brownsville

Tucson

Tijuana

San Diego

Nuevo Laredo

Nogales

Nogales

Matamoros

Laredo

0 50 100 150 200 KILOMETERS

Base from U.S. Geological Survey 0 50 100 150 200 MILES

GTOPO30 (Global 30 Arc Second Elevation Data)

Ecological regions of North America data from

Commission for Environmental Cooperation

ecoregions

Challenge Theme 1. Understanding and Preserving Ecological Resources 43

Figure 3–1. Ecological regions along the United States–Mexican border.
44 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Biological Status and Trends

Nongovernmental organizations, biological resource trustees, and regulatory agencies in 

the United States and Mexico are trying to manage the loss of local populations of species in 

addition to the extinction of species in the broader area of the Borderlands. In the U.S. portion 

of the Borderlands alone, 168 species—81 plant, 19 bird, 14 mammal, 23 fish, 10 reptile,

7 amphibian, and 14 invertebrate—are listed as threatened or endangered by the U.S. Fish and 

Wildlife Service (2009a). For many of these species, fundamental biological, ecological, and 

population data are not available. Obtaining these data becomes more difficult for biologists

who must contend with the issues of species rarity, private lands, international politics, and the 

dangers of working in a region where there is criminal trafficking of goods, animals, and people.

Many species of birds, bats, and insects pass through the Borderlands in route to breeding 

or feeding areas. The lesser long-nosed bat (Leptonycteris yerbabuenae) migrates north in the 

spring from fall and winter roosts in south-central Mexico to spring and summer maternity 

roosts in the Sonoran Desert of Arizona and California. These bats have a mutualistic relationship 

with species of agave and the saguaro (fig. 3–2), and their foraging activities and migratory

movements are dependent on the presence of these plants along an intact migration corridor. 

Migratory birds utilize the entire region as stopover habitat during migration (Skagen and 

others, 2005; Paxton and others, 2007), and many species winter in this region. For example, 

the Pacific Flyway brant (Branta bernicla) winters in the Colorado River delta where expansive 

marshes and mudflats historically have provided sufficient food resources. Today, only 20 percent

of the Colorado River delta’s wetlands remain (Glenn and Zamora-Arroyo, 2001). Loss of 

wetland habitats needed by the Pacific Flyway brant and many other species is largely caused

by regulation of the Colorado River by dams, which reduce the river’s flow and thus the

replenishment of associated nutrient-rich sediments to the delta. Increased salinity and 

contamination of the Colorado River delta are also implicated in the decline of the vaquita 

(Phocoena sinus), a rare porpoise species endemic to the upper Gulf of California.

Gilded woodpecker 

(Colaptes chrysoides)

Pacific Flyway brant

(Branta bernicla)

House finch

(Carpodacus mexicanus)
long-nosed bat

Figure 3–2. A lesser long-nosed bat (Leptonycteris yerbabuenae) 

prepares to collect nectar from a saguaro (Carnegiea gigantea) 

(bottom). These bats have specialized anatomy (top)—elongated 

rostrums, long brush-tipped tongues, and a reduced number of 

teeth—that allows them to feed on the nectar and pollen of the 

saguaro (Fleming and others, 2001). 
For songbirds that breed in the United States or Canada but winter in 

the Caribbean or Central or South America, the act of migrating is physically 

demanding in terms of the energy needed. Because of their small size, many 

Neotropical migrant warblers are unable to carry sufficient reserves to 

migrate nonstop and thus must select locations to stop and refuel. Choosing 

appropriate stopover locations is important to ensure that individuals survive 

migration and reach their destinations in good condition. Although birds are 

known to actively choose when and where to stop (Hutto, 1985), little is known 

about how individuals judge the quality of potential stopover locations.

For example, birds prefer locations with an abundance of food, such as 

insects, yet the signs or cues that birds use to determine food availability 

remain largely unknown. One possibility is that birds determine food availability 

from the types or condition of local trees. The species of tree or changes in 

the phenology of a tree (for example, flowering, leaf-flush, fruiting, leaf-loss) 

may present birds that eat insects with an obvious and reliable predictor of 

insect abundance. Scientists with the USGS Sonoran Desert Research Station 

in Tucson, Ariz., have tested this possibility by monitoring stopover locations 

of 28 species of insectivorous Neotropical migrant songbirds at the Cibola 

National Wildlife Refuge (U.S. Fish and Wildlife Service) along the lower Colorado 

River and the San Pedro Riparian National Conservation Area (Bureau of Land 

Management) on the San Pedro River in southern Arizona (McGrath and van 

Riper, 2005).

In this study (McGrath and van Riper, 2005), USGS researchers were able 

to show for the first time that the flowering phenology of a common tree species, 

honey mesquite (Prosopis glandulosa), acts as a reliable cue for migrant birds 

at both local and landscape scales. That the flowering phenology of honey 

mesquite is a reliable indicator of actual food availability indicates the importance 

of this cue for migrant bird populations, at least along the San Pedro and 

Colorado Rivers. It remains unclear how the phenology of honey mesquite 

or other trees may influence other important migratory corridors that differ 

geographically, have different migratory peaks, and support different population 

and species assemblages. Future research should focus on the generality of 

this pattern and how climate change and invasion by exotic trees may alter 

settlement cues and thus adversely affect migrant species.

(Facing page) The Nashville warbler (Vermivora ruficapilla) (bottom 

left and right) is a Neotropical migrant bird species. Some of its 

major migratory pathways travel through the United States–Mexican 

border region (top; modified from Lowther and Williams, 2011). 

A Migrant Bird ’s Dilemma

. . . .facing the challenge
EXPLANATION

Breeding range

Wintering range

Migration routes

Challenge Theme 1. Understanding and Preserving Ecological Resources 47
48 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Carnivorous mammals are at particular risk in the Borderlands. Their wide-ranging 

movements and sensitivity to habitat fragmentation make them susceptible to decreases in 

the availability of suitable corridors to sustain the animals’ movements. Like a keystone that 

secures the stability of a structural arch, these keystone mammalian species are critical to the 

health of an ecosystem and to the maintenance of biodiversity in the Borderlands. Although 

many native carnivores in the Borderlands had disappeared or declined to near extinction by 

the early 1900s (Cockrum, 1982), a few species have maintained populations in the wilder 

parts of northern Mexico, and there is hope they can expand their ranges into protected areas in 

the United States. Species with ranges that extend north into the Borderlands include the black 

bear (Ursus americanus), the Mexican gray wolf (Canis lupus baileyi), the jaguar (Panthera 

onca), and the ocelot (Leopardus pardalis). For example, ocelots have a tenuous hold in south 

Texas (fig. 3–3), and jaguars are infrequently found just north of the Arizona-Sonora border.

Coyote (Canis latrans)

Grey wolf (Canis lupus)
Figure 3–3. The photo of an ocelot adult and kitten (top) was 

taken by remote camera at the Laguna Atascosa National Wildlife 

Refuge, Texas, in 2008 and is the first time a mother and baby have 

been photographed together. The ocelot (Leopardus pardalis) 

(bottom) is an endangered species; fewer than 100 remain in the 

United States. 

Challenge Theme 1. Understanding and Preserving Ecological Resources 49

ocelot
The current range of the black bear (Ursus americanus) in the Borderlands 

is patchy and extends into southern Texas, New Mexico, Arizona, and Mexico, 

the southern end of the black bear range where they are endangered. The 

bears of this region commonly move between what are often called sky 

islands. The isolated mountain ranges of the Madrean Archipelago (fig. 3–1) 

form these ecosystem islands that serve as stepping stones for the movement 

of black bears through this region. The varied topography and extreme elevation 

gradients in the sky island ranges of the Madrean Archipelago have resulted 

in a rich flora and fauna (Toledo and Ordonez, 1993). Construction along the 

United States–Mexican border, such as border fences, can prevent the movements 

of the black bear across the border, could truncate their range or interrupt a 

contiguous distribution, and could lead to the retraction of this species’ range 

away from the border.

The use of nonintrusive techniques to obtain DNA would allow for a better 

understanding of the population genetics of the black bear in the Borderlands, 

which could have a critical role in ensuring the survival of this species in 

the southern extent of its range. Researchers with the USGS West Glacier 

Field Station of the Northern Rocky Mountain Science Center in Montana are 

using recent advances in genetic technology to extract DNA from grizzly bear 

(Ursus arctos ) hair and scat without having to capture and handle the bears 

(Roon and others, 2005); these procedures could be used similarly to study the 

black bear populations in the Borderlands. Reliable bear population estimates 

can be determined in a nonintrusive manner, and the DNA collected from the 

samples can be used to evaluate the degree of genetic variation and relatedness 

of individuals.

The temperate and tropical species that survive in the arid and often 

rugged border environment live in habitats not typical to their species, 

contrasting sharply with the habitats of species populations living farther 

north or south. Survival of a species in a great range of habitat types may be a 

key element in that species’ long-term survival and continued evolution, 

particularly when having to adapt to human-induced and natural climate 

changes. Construction along the border could prevent terrestrial vertebrates 

from moving across the border, which would likely be detrimental to our ability 

to preserve the health and continued function of ecosystems along this zone.

Bears and Sky Islands 

in the Southwest

(Continued on page 52)

. . . .facing the challenge
Challenge Theme 1. Understanding and Preserving Ecological Resources 51

In the Borderlands, the black bear (bottom right) makes its habitat 

in the sky islands of the Madrean Archipelago, which includes 

areas such as Saguaro National Park near the Rincon Mountains 

(top left), the Chiricahua Mountains (top right), and the Santa 

Catalina Mountains (center).
Historical Range of Black Bear in North America

Range of Black Bear in North America in 1995

black bear

A juvenile black bear (Ursus americanus) (left) and a female black bear (right) with maps showing 

the change in the range of black bears in North America, historically (top center) and in 1995 

(bottom center; both modified from Vaughan and Pelton, 1995).
Challenge Theme 1. Understanding and Preserving Ecological Resources 53
Many native species that live in and near streams, rivers, and springs are also struggling 

in the Borderlands. Years of groundwater withdrawals, the operation of dams and reservoirs, 

diversions of river flows, competition from nonnative species, and habitat loss have all negatively

affected many native species associated with aquatic habitats in the Borderlands. The federally 

endangered desert pupfish (Cyprinodon macularius) inhabits desert springs, cienagas, and small 

streams of the lower Gila and Colorado Rivers in Arizona, California, and Mexico (Center for 

Biological Diversity, 2011). Threats to the remaining five populations of this species include

competition from nonnative fish, dam construction, livestock grazing, stream channelization,

and aerial spraying of pesticides. Increases in the populations of nonnative species of fish and

the bullfrog (Lithobates catesbeianus) correspond with a decline in populations of the 

narrow-headed garter snake (Thamnophis rufipunctatus) of Arizona, New Mexico, and northern 

Chihuahua (Pierce, 2007). The predicted effects of climate change are likely to worsen the 

already precarious existence of many of the Borderlands’ rare and imperiled amphibians, such 

as the California red-legged frog (Rana draytonii), the Chiricahua leopard frog (Lithobates 

chiricahuensis), and the Tarahumara frog (Lithobates tarahumarae), among others.

Native plant species and terrestrial plant communities along the border are exposed to 

many threats from agriculture, suburban sprawl, wildfire, poaching, grazing, off-road vehicles,

and nonnative plants. The invasion of nonnative plants can affect ecosystem structure and 

function by altering resource availability, soil stability and rates of erosion, accumulation of 

litter and salts, and natural fire regimes (Freeman and others, 2007). Along the Rio Grande in 

south Texas, near where the river reaches the Gulf of Mexico, 95 percent of the native thorn 

forest habitat has been lost with only a few “islands” of native habitat remaining. This part of 

the Borderlands is ecologically important because it is a crossroads of the climates of the 

subtropical Gulf Coast, the semiarid Great Plains, and the arid Chihuahuan Desert (U.S. Fish 

and Wildlife Service, 2009b). On the other end of the Borderlands, Arizona and southern 

California are combating buffelgrass (Cenchrus ciliaris), an invasive species that easily dominates 

native grasses (fig. 3–4). Buffelgrass spreads quickly, and because it grows densely, it can be a

serious fire hazard. Many areas of the Sonoran Desert, once known for beautiful spring flowers,

are now carpeted only with buffelgrass.

Climate change in the United States–Mexican border region is predicted to have a 

profound influence on existing biota (flora and fauna populations), both spatially and temporally.

Increased rates of desertification in the Sonoran and Chihuahuan Deserts, both of which cross

into the Borderlands, would adversely affect the biota of this area. The Chihuahuan Desert has 

the highest diversity of plants of any desert region on Earth (Chihuahuan Desert Research 

Institute, 2012). Even though desert biota are well adapted to extreme fluctuations in daily

temperature and seasonal rainfall, their adaptability is not limitless. With desert temperatures in 

the Borderlands predicted to rise by the end of the century and rainfall to decrease by 2071–2100 

(United Nations Environment Programme, 2006), some species may not be able to survive (see 

chapter 10 for more information). Climate change in the Borderlands would certainly accelerate 

the reduction in water availability for human and ecological needs. These changes would take 

place in a region whose population and thus water needs would continue to grow, particularly 

the San Diego–Tijuana (California–Baja California), Nogales-Nogales (Arizona-Sonora), and 

El Paso–Ciudad Juárez (Texas-Chihuahua) sister city areas.

Desert pupfish

(Cyprinodon macularius)
Mexican bluewing (Myscelia ethusa)
buffelgrass

56 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Figure 3–4. Buffelgrass 

(Cenchrus ciliaris) (facing page) 

is an invasive species that 

encroaches on native plant 

habitat. In Saguaro National Park 

in Arizona, buffelgrass surrounds 

a young saguaro cactus at the 

Javelina picnic area (top left; 

April 1998). In Sonora, 30 miles 

north of Hermosillo, buffelgrass 

has spread from cultivated 

buffelgrass pastures to rocky 

hillsides and native desert scrub 

(bottom left; January 1997). 

The 470-kilometer (292-mile) reach of the Rio Grande from El Paso to 

Presidio, Tex., is recognized as the most dewatered reach of the river and has 

been referred to by some people as the Forgotten Reach. Annual flows in this 

reach are about one fifth of flow levels before regulation, and the historic late 

spring and early summer floods driven by snowmelt from the Rocky Mountains 

of southern Colorado and northern New Mexico have been all but eliminated 

(Collier and others, 1996). Because upstream regulation has reduced the 

occurrence of over-bank floods in the Forgotten Reach, monocultures of salt 

cedar (also known as tamarisk) have displaced the native gallery of willow 

(Salix spp.) and cottonwood (Populus spp.) in the riparian and floodplain habitats. 

Salt cedar is an exotic species introduced from southern Eurasia more than 

100 years ago as an ornamental shrub and a method of controlling bank erosion. 

Once salt cedar becomes dominant in a given environment, the river channel 

becomes aggraded as the dense thickets of salt cedar trap sediment 

(Sudbrock, 1993), resulting in a narrower, simplified channel and thus uniform 

flow velocities, armored streambeds and bank slopes, and a less diverse fish 

assemblage and aquatic invertebrate community. Moreover, dense stands 

of salt cedar inhibit recolonization by native vegetation and can reduce the 

diversity of birds, rodents, and insects in riparian-floodplain habitats. 

Contemporary studies of evapotranspiration of riparian plants indicate that 

salt cedar and native riparian species, such as the cottonwood, transpire 

about the same amount of water (Shafroth, 2010). However, because salt 

cedar can grow in places higher above the water table than native riparian 

species, the total plant transpiration where salt cedar and native species are 

mixed can be higher (Grubb and others, 2006).

The issues associated with salt cedar and river management are among 

the topics addressed by the riverine science program at the USGS Fort Collins 

Science Center (FORT; http://www.fort.usgs.gov/WaterWrks/). The program 

brings together scientists specializing in various aspects of ecosystem science, 

allowing for multidisciplinary approaches to complex questions. The goal 

of the FORT riverine science program is to support river management 

decisionmaking by studying the relations between management actions and 

riverine ecosystems, for example, the response of invasive species such 

as salt cedar to altered flow regimes. Other examples of areas of FORT salt 

cedar research include managing areas overwhelmed by salt cedar through 

removal and revegetation and planning restoration for areas in the West 

where salt cedar has been controlled.

Salt Cedar and the 

Forgotten Reach

. . . .facing the challenge
Salt cedar (Tamarix ramosissima) (background and top right) dominates the channel and floodplain 

of the Forgotten Reach, the portion of the Rio Grande between El Paso and Presidio, Texas (bottom 

left). As an invasive species, it competes with native flora for riparian resources. 
 USGS Capabilities

The United States–Mexican border region boasts the highest diversity of desert plants 

in the world, the largest number of bird species in North America, and some of the most wild 

and remote places in the United States and Mexico. These unique biological resources are at 

risk of habitat loss and fragmentation by barriers inhibiting dispersal and migration routes, the 

dewatering of rivers and streams, and other stressors influenced by global climate change.

The U.S. Geological Survey (USGS) has unique capabilities that can help bring the best science 

to many of the most perplexing and critical issues associated with the ecological resources of 

the Borderlands.

Scientists with the USGS conduct 

research that assists resource managers in 

preventing the loss of species and recovering 

and protecting aquatic and terrestrial habitat. 

Scientists at the USGS Southwest Biological 

Science Center and the Arizona Cooperative 

Research Unit at the University of Arizona 

use genetics to detect historical and current 

wildlife connectivity across the United States–

Mexican border. With DNA1 fingerprinting,

they monitor populations of American beaver 

(Castor canadensis), jaguar (Panthera onca), 

and puma (Puma concolor). Using remote 

sensing techniques, hair samples, and scat they 

identify the presence and ranges of mammal 

populations that move across the border.

1

 DNA—deoxyribonucleic acid.

Curve-billed thrasher (Toxostoma curvirostre)

Mexican Jay 

(Aphelocoma ultramarina)
Challenge Theme 1. Understanding and Preserving Ecological Resources 61

Scientists with the USGS Southwest Biological Science Center’s Sonoran Desert 

Research Station focus on the importance of connectivity between avian breeding and 

nonbreeding sites. These researchers use advanced telemetry, chemical isotopes, and molecular 

markers to better understand migratory connectivity (Paxton and Van Riper, 2006). The 

USGS is recognized internationally for developing state-of-the-art techniques for monitoring 

the migratory routes of birds; for example, the miniaturization of radio transmitters has 

greatly increased monitoring capabilities.

A vegetation-association geographic information system (GIS) database for Arizona has 

been developed by the USGS Arizona Gap Analysis Project to evaluate long-term maintenance 

of biodiversity (Kunzmann and others, 1998; Thomas and others, 2006). Base vegetation 

coverage was developed using Thematic Mapper imagery (1990–1992), and vegetation 

associations were classified using airborne sample points referenced to the global positioning

system (GPS) and on-ground plant sampling to correct classification errors. For species such as

the nectar-feeding lesser long-nosed bat, the database can identify the occurrence of or changes 

in host plants along “nectar corridors” from southern Arizona to Mexico.

Under the Weeds of the West initiative, USGS researchers with the Western Ecological 

Research Center and the Southwest Biological Science Center develop methods to better 

detect, monitor, and predict the effects of invasive species. For example, their research on salt 

cedar (Tamarix ramosissima) improved the understanding of ecological interactions related to 

the biological control of this invasive plant and of the overall ecological and political implications 

of salt cedar invasion in desert wetlands (van Riper and others, 2008).

The Policy Analysis and Science Assistance Branch at the USGS Fort Collins Science 

Center provides expertise for the management of natural resources through biological, social, 

economic, and institutional analyses of conservation policy and management practices (Fort 

Collins Science Center, 2009). The focus of these scientists is to integrate research in biology, 

sociology, and economics to inform resource managers in a way that will help resolve resource 

management conflicts. The FORT Center serves an integral role in assisting scientists and

resource managers to balance highly complex and sensitive issues in the biologically, 

sociologically, and economically diverse Borderlands.

Jaguar (Panthera onca)

Researchers with the U.S. Geological Survey and National Park Service camping in the Lower 

Canyons along the Rio Grande
62 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Western coachwhip snake (Masticophis flagellum testaceus )

Black-tailed rattlesnake 

(Crotalus molossus) 
Challenge Theme 1. Understanding and Preserving Ecological Resources 63

Scientists with the USGS Texas Water Science Center are collaborating with the National 

Park Service in Big Bend National Park, the U.S. Fish and Wildlife Service, and the Reserva 

de la Biosfera Maderas del Carmen [biosphere reserve] and the Área de Protección de Flora y 

Fauna Cañón de Santa Elena [protected flora and fauna area] in Mexico to evaluate available 

habitat of the federally endangered Rio Grande silvery minnow (Hybognathus amarus). U.S. 

Geological Survey scientists are field mapping the available habitat of the minnow over a range

of river flows critical to spawning and dispersal of various life stages of this species.

The USGS has the scientific expertise to study the biology and ecology of biota, apply

and develop ecological indicators, conduct baseline biological inventories, and establish 

long-term monitoring programs in the Borderlands. The USGS has expertise in the fields of

remote sensing, geospatial imagery, and landscape-level analyses, which is highly applicable to 

solving resource problems along the border. The unique and diverse biological resources along 

our southern geopolitical boundary provide a positive collaborative opportunity for the United 

States and Mexico to conduct mutually beneficial research and monitoring of biota in a region

that will continue to experience severe ecological stress into the foreseeable future.

A primary focus of the USGS Climate and Land Use Change Program is to evaluate 

the effects of climate and land-use change on U.S. Department of Interior (DOI) lands and 

resources. The large number and broad geographic extent of DOI lands in the Borderlands 

provide a unique opportunity for the USGS to study the effects of climate and land-use change 

on the ecological resources of this region on a broad scale. Research efforts with application in 

the Borderlands include (1) addressing the interaction of climate change and other environmental 

factors with invasive plant infestations in the arid Southwest; (2) predicting the responses, 

sensitivities, thresholds, resistance, and resilience of western mountain ecosystems to climatic 

variability and change; and (3) predicting the response of semidesert vegetation to predicted 

climate change along regional gradients in the arid Southwest.

One example of a USGS project that has broad applications for the Borderlands, particularly 

on DOI lands, is the effort to determine the causes and consequences of climate change on the 

distribution and habitat selection of migratory birds (Lloyd and others, 2006). The principal 

focus of this project is to use localized climatic gradients, or microclimate gradients, as small-scale 

versions of climate gradients that occur over larger areas. By studying the distribution, habitat 

selection, and biological interactions of bird species along microclimate gradients, such as 

mountainsides and hill slopes, USGS scientists can provide important insights into climate 

influences on species at larger geographic scales that are more difficult to study.

References cited in this chapter are listed in chapter 12.
Challenge Theme 2.

Assuring Water Availability and Quality 

in the 21st Century

By James Callegary, Jeff Langman, Jim Leenhouts, and Peter Martin 

Along the United States–Mexican border, the health of communities, 

economies, and ecosystems is inextricably intertwined with the availability 

and quality of water, but effective water management in the Borderlands 

is complicated. Water users compete for resources, and their needs are 

increasing. Managers are faced with issues such as finding a balance 

between agriculture and rapidly growing cities or maintaining public 

supplies while ensuring sufficient resources for aquatic ecosystems. In 

addition to human factors, the dry climate of the Borderlands, as compared 

to more temperate regions, also increases the challenge of balancing 

water supplies between humans and ecosystems. Warmer, drier, and 

more variable conditions across the southwestern United States—the 

projected results of climate change (Seager and others, 2007)—would 

further stress water supplies. 

Chapter 4
Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 65
66 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

International Boundary and Water Commission

water control structures on the United States–Mexican border
Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 67

Adding to the complexity of water availability, resource managers must address and attempt to balance the complicated 

interweaving of interstate compacts, international treaties, Native American water rights, and the water needs of ecosystems 

and endangered species. Rivers and aquifers cross both state and international boundaries and are shared between Mexican and 

United States communities. The few major rivers of the Borderlands are either currently under adjudication (with thousands of 

legal claims that are taking decades to sort out and have no end in sight) or their waters were divided up decades ago by international 

treaties and domestic laws. 

Water quality also contributes to the issues facing water resource managers. Population increases and the growth of urban 

areas in the last fifty years not only have caused increased water use but also have dramatically increased contamination of water

supplies. One source of contamination is increased flooding. As cities grow, so does the presence of impermeable surfaces such

as streets, parking lots, and buildings. Water from these surfaces can contain high levels of contaminants from automobile and 

industrial sources (Mahler and van Metre, 2011). Because water cannot permeate these surfaces, it runs off into lakes (Wilson 

and others, 2006) and into stream channels where it can adversely affect aquatic and riparian life and infiltrate bed sediment,

sometimes reaching groundwater and bringing contamination along with it. 

National Park Service staff at

Amistad National Recreation

Area, Texas
Unfortunately, knowledge of the availability, sustainability, quality, and interaction of 

surface waters and groundwaters is limited or nonexistent in some areas of the Borderlands. 

Many border communities use groundwater at rates that are unsustainable. Increased withdrawals 

exceed aquifer replenishment by rain and snowfall (Arizona Department of Water Resources, 

2012), and water tables have dropped in many locations, drying up rivers and requiring farmers 

and cities to redrill and deepen their wells. As a result, there is a sense of urgency in the 

Borderlands as communities struggle to find and secure the adequate supplies of good quality

water needed to sustain future generations.
To address these challenges and provide science for possible solutions, the U.S. Geological 

Survey (USGS) has been working to identify contaminated water and its potential effects on 

ecosystems and people, help communities find additional supplies, and monitor river flow

to provide timely flood warnings and to ensure the United States meets its treaty obligations

(Asquith and Heitmuller, 2008; Norman and others, 2010b; Jagucki and others, 2011; Tillman 

and others, 2011). The USGS establishes connections with and provides scientific and

technical information to cities, counties, States, and Federal agencies such as the National 

Weather Service, the Bureau of Reclamation, the U.S. Environmental Protection Agency, and 

the U.S. Department of Homeland Security to aid them in their work in mitigating flood hazards

and providing clean, sustainable water for the communities they serve. The USGS negotiates 

agreements and works with partners in Mexico to study shared water supplies and water quality 

so that both countries can make informed collaborative decisions about management of water 

resources. The Transboundary Aquifer Assessment Program (TAAP) is an example of just 

such a collaborative international effort (U.S. Congress, 2006). Enacted by Congress in 2006, 

TAAP is a partnership of the USGS and the Water Resources Research Institutes in Texas, 

New Mexico, and Arizona. The scientists working on TAAP collaborate with Federal, State, 

and local entities on both sides of the border, including the International Boundary and Water 

Commission, universities, and nongovernmental organizations, to answer the questions identified

by water managers as being of critical importance to the use and understanding of aquifers 

shared by the United States and Mexico (Megdal and Scott, 2011). Topics of concern include 

the need to understand the structure of critical transboundary aquifers and the distribution of 

sediments within them, the need to understand how urbanization affects recharge to aquifers, 

and the need for new and improved computer models of water flow and contaminant transport

on both sides of the border. The USGS is currently addressing all of these questions. The TAAP 

program participates in the United Nations Educational, Scientific, and Cultural Organization

(UNESCO) Internationally Shared Aquifer Resource Management Initiative, which aids and 

supports member groups by improving understanding of the scientific, institutional,

environmental, socioeconomic, and legal issues associated with transboundary aquifers 

worldwide. As an example of USGS efforts to address the complex interaction among people, 

animals, ecosystems, water, and pollution across the border, the USGS Border Environmental 

Health Initiative (BEHI; http://borderhealth.cr.usgs.gov) has been working with United States 

and Mexican agencies to assess aquatic ecosystems for contaminants present in treated effluent

discharged into rivers and streams (Norman and others, 2010a) and with public health officials

to develop, collect, and serve to the public and public health officials data of particular

relevance, such as location and rates of infectious disease (Norman and others, 2012). 

Multidisciplinary teams of BEHI scientists are working to assess the effect on humans and 

aquatic ecosystems of pharmaceuticals and personal care products present in treated effluent

discharged into Borderlands rivers and streams. The TAAP and BEHI efforts are but two of 

many examples of water-focused projects that demonstrate the expertise of the USGS and the 

substantial contribution it makes to improving the health and well-being of people and 

communities along the United States–Mexican border.
water

70 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Status of Resources

The Borderlands region is characterized by a large diversity of natural environments, 

ranging from coastal basins to deserts, and of human populations, ranging from dense urban 

complexes to sparsely populated rural areas. Yet the scarcity of water unifies them all. From

California to Texas, the dominant climate is semiarid to arid characterized by low precipitation, 

low groundwater recharge, and frequent drought conditions. Water resources in the 

Borderlands are controlled by physiographic, geologic, and hydrologic characteristics, 

which were used to identify the eight subareas used in this report (see chapter 2): the 

varied geology and topography of the coastal plains, the Peninsular Ranges, and the 

Salton Trough control water resources in subarea 1; Basin and Range geology 

controls both the location of rivers and the geometry of aquifers in subareas 

2 through 4; and the Rio Grande and its tributaries dominate the hydrology in 

the eastern portion of the Borderlands. In subareas 5 through 8, the river forms 

the international border in Texas from El Paso to Brownsville and ultimately 

flows into the Gulf of Mexico. Although the Borderlands are described in

this chapter as multiple subareas—each with its own specific hydrologic

issues—water is a limiting resource throughout the entire border 

region. In fact, consumptive use ranges from about 35 percent 

of renewable supplies in California to 103 percent in the Lower 

Colorado, indicating an ongoing deficit (fig. 4–1). To ensure the

viability and sustainability of people and the environment to which 

we are inextricably linked, improved knowledge of the quality and 

availability of water resources in the Borderlands (fig. 4–2) is needed as

populations continue to increase along the border.

Figure 4–1 (facing page). Average consumptive water use 

compared with renewable water supply for water resources 

regions in the western United States. The Lower Colorado and 

Rio Grande water resources regions are the only regions in the 

United States that consume 40 percent or more of their renewable 

supply. Over half of the U.S. regions use 10 percent or less. 

Modified from Anderson and Woosley (2005).
1

2

3

4

5

6

7

8

TEXAS

CALIFORNIA

NEVADA

UTAH COLORADO

OREGON

WASHINGTON

IDAHO

MONTANA

WYOMING

NORTH DAKOTA

SOUTH DAKOTA

NEBRASKA

KANSAS

ARIZONA OKLAHOMA

NEW MEXICO

SONORA

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA

UNITED 

MEXICO

STATES

PACIFIC

OCEAN

Gulf

of

Mexico

Gulf of California

0 125 250 175 500 KILOMETERS

0 125 250 375 500 MILES

UPPER

 COLORADO

4.2

13.9

LOWER

 COLORADO

10.6

10.3

RIO GRANDE

3.8

5.4

TEXAS GULF

9.1

33.1

CALIFORNIA

25.8

74.6 ARKANSAS-WHITE-RED

9.6

68.7

SOURIS-RED-RAINY

0.5

6.5

MISSOURI

17.5

62.9

GREAT BASIN

3.5

10.0

PACIFIC NORTHWEST

11.2

276.2

Consumptive use as a percentage of renewable supply

0 – 10

10 – 40

40–100

Greater than 100

Volume, in billion gallons per day

1995 consumptive use

Renewable water supply

International boundary

EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

1

3.8

5.4

Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 71
Alamo River

New River

Whitewater River

Coachella Canal

All-American Canal

COLORADO RIVER

Gila River

Salton

Sea

RIO GRANDE

RIO GRANDE

RIO BRAVO

PACIFIC OCEAN

Gulf

of

Mexico

Gulf of California

San Pedro River

Santa

Mimbres

River Cruz

River

Rio Salado

Rio San Rodrigo 

Conchos

Rio

River

Pecos River

Pecos River

Elephant Butte Reservoir

Amistad Reservoir

Falcon Reservoir

Devils 

Rio Álamo

International Dam

Amistad Dam

Caballo Reservoir

Rio Bavispe 

Rio Salinas

San Juan 

Rio 

Laguna Madre

Parker

Dam

Lake

Havasu

Elephant Butte Dam

Painted Rock

Dam

Rio San

Rafael 

Rio Sonoyta

Verde River

Rio Magdalena

Rio 

Sonora 

Rio Casas Grandes 

River

Nueces

Rio San 

Ferna ndo

Brazos

River

Arroyo Colorado

Falcon Dam

Laguna Madre

Tijuana River

basin

Imperial Valley

Mexicali Valley

San Pedro

basin

Douglas

basin

Willcox

basin

Santa Cruz

basin Mimbres

basin

Mesilla basin

Hueco

bolson

EDWARDS-TRINITY

AQUIFER

GULF COAST

AQUIFER

1

2

3

4

5

6

7

8

Yuma

San

Luis

Tucson

Nogales Douglas

Tijuana

San Diego

Agua Prieta Nogales

Los Angeles

Phoenix

Ciudad

Juárez

El Paso

Las Cruces

Ojinaga Hermosillo

Chihuahua

Albuquerque

Laredo

Presidio

Eagle Pass

Brownsville

Ciudad

Acuña

Nuevo

Laredo

Piedras Negras

Matamoros

Ciudad Victoria

Austin

San Antonio

Corpus Christi

Monterrey Saltillo

Del Rio

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

SONORA

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA

110°

35°

30°

100°

105°

115°

25°

EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

Drainage basin—U.S. Geological Survey HYDRO1k

International boundary

1

0 125 250 KILOMETERS

0 125 250 MILES Base from U.S. Geological Survey

National Atlas of the United States, 2001,

and Mexico Instituto Nacional de Estadistica,

Geografia, e Informática, 2000, digital data

Albers Conical Equal Area Projection

North American Datum of 1983 (NAD83)

Shaded relief from U.S. Geological Survey

GTOPO30 (Global 30 Arc Second Elevation Data)

MEXICO

UNITED STATES

Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 73

Figure 4–2. Major drainage basins and waterbodies in the eight 

subareas of the United States–Mexican border region. The border 

region subarea boundaries are based on watershed areas used by 

the U.S. Geological Survey Border Environmental Health Initiative. 
74 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Pacific Basins and Salton Trough

The Pacific Basins–Salton Trough subarea (subarea 1; fig. 4–2) includes the coastal basins

encompassing San Diego and Tijuana and the desert basins of the Imperial and Mexicali Valleys 

in the Salton Trough. Local water resources are limited because precipitation is low, and much 

of the water used in this subarea is imported. A large portion of the area’s water resources comes 

from the Colorado River, which provides substantial irrigation to agricultural lands in California, 

Arizona, and Mexico. The San Diego–Tijuana metropolitan area is one of the most heavily 

populated areas along the border (combined population of more than 4 million). Groundwater 

supply is limited in the coastal area, and the most productive aquifers are Quaternary alluvial 

deposits that are generally less than 46 meters (m) (150 feet [ft]) thick (Izbicki, 1985). The 

Tijuana River basin crosses the international border, with about 72 percent of the basin in 

Mexico and 28 percent in the United States. Groundwater quality in the Tijuana River basin 

is poor because of excessive groundwater mining that occurred from the 1950s through the 

1970s—when more groundwater is pumped than recharged in coastal aquifer systems, saltwater 

intrudes into the groundwater supply area.

The lowest part of the Salton Trough is the Salton Sea, which was accidentally filled by a

canal levee break in 1905. It currently receives surface-water inflow from the New and Alamo

Rivers originating in Mexico (fig. 4–2) and agricultural runoff from land in the United States.

Numerous studies have documented elevated levels of pesticides in the water and sediments carried 

by these water sources (Eccles, 1979; Setmire, 1984; Schroeder and others, 1988; Setmire and 

others, 1990; Michel and Schroeder, 1994; Crepeau and others, 2002; Leblanc and others, 2004 

a, b; Orlando and others, 2008). Because of the contamination, groundwater is unsuitable for 

domestic and irrigation uses without treatment. The valley’s agricultural productivity relies on 

imported Colorado River water, which recharges groundwater through irrigation and seepage 

from canals that carry the water from the river to the agricultural areas (Loeltz and others, 1975).

Imperial Dam, Colorado River

Salton Sea

Tijuana River Reservoir

Subarea 1.
A salt-encrusted tree

in the Salton Sea
76 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Colorado River and Gulf of California, 

Mexican Highlands, and San Basilio and Mimbres

The Colorado River–Gulf of California, Mexican Highlands, and San Basilio–Mimbres 

subareas (subareas 2, 3, 4; fig 4–2) are within the Basin and Range physiographic province

(Anderson, 1995). Surface-water resources in these subareas have either been completely 

allocated through legal compacts and water-right agreements or are the subject of a decades-long 

legal process (adjudication) to decide water rights (Arizona Department of Water Resources, 

2007). The Colorado River, the largest river in this area, has a median annual flow of over

9 billion cubic meters (m3) (about 7.3 million acre-feet [acre-ft]) as measured from 1935 to 

2008 below Lake Havasu and Parker Dam (U.S. Geological Survey, 2009). A total of about 

1.9 billion m3 (1.5 million acre-ft) are appropriated for flow across the international boundary

into Mexico (Arizona Department of Water Resources, 2008), and more than 1.7 billion m3

(1.4 million acre-ft) are diverted into the Central Arizona Project, along with additional 

diversions to the All-American Canal, which diverts water to the Salton Trough. So much flow

is diverted from the Colorado River that, in years without a flood, water from the river almost

never reaches the Gulf of California (Cohen and Henges-Jeck, 2001).

Most of the available surface-water

and groundwater resources in the area 

are the result of episodic recharge 

from spring snowmelt and summer 

thunderstorms or of effluent from

wastewater treatment plants. Much of 

the precipitation and runoff, however, 

comes from monsoon thunderstorms, 

rapid snowmelt, or hurricanes, which 

can have large negative effects on 

human populations and riparian and 

aquatic ecosystems. Though these 

events contribute to the available water 

supply, flooding and mobilization of

sediments can quickly alter the shape 

and size of rivers and stream channels 

and can transport contaminants to 

downstream lakes, reservoirs, and 

ecosystems and into vulnerable aquifers.

Palo Verde Diversion Dam, Colorado River

New Waddell Dam, part of the 

Central Arizona Project

Parker Dam, Colorado River

Subareas 2, 3, and 4.
Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 77

In many locations within these three subareas, groundwater mining has caused water 

tables in the aquifers to decline. Some aquifers are becoming more saline because of intrusion 

of deeper, salty groundwater into pumped aquifers. Arizona and New Mexico groundwater 

resources are estimated to be depleted annually by about 3.1 billion m3 (2.5 million acre-ft) and 

1.6 billion m3 (1.3 million acre-ft), respectively, resulting from combined municipal, industrial, 

and agricultural usage (Wilson and others, 2003). Evapotranspiration is also a substantial factor 

in water budgets for this arid and semiarid region. 

Aside from the Colorado River, the major drainage systems are the San Pedro, Bavispe, 

Santa Cruz, Gila, and Mimbres Rivers, though each has at least one ephemeral or intermittent 

section along its course. The major aquifers are found within alluvial deposits of the Colorado, 

Willcox, Douglas, San Pedro, Santa Cruz, Gila, and Mimbres basins. These aquifers contain 

substantial volumes of water in storage, but annual recharge is low, so groundwater in this 

region is largely a nonrenewable resource. Before water-resource development, the Santa Cruz, 

San Pedro, and Gila Rivers had sustained flow for most of the year in some reaches. Groundwater

pumping and surface-water diversions and impoundments for agricultural and municipal uses, 

however, have substantially decreased water levels and have captured groundwater that once 

flowed to streams and rivers (see special section on capture maps, p. 84) (Hoffmann and Leake,

2005; Thomas and Pool, 2006; Webb and others, 2007). As a result, rivers such as the Santa 

Cruz have become almost entirely dependent on effluents for their water supply for most of the

year, and the change in source water has created substantial negative effects on water quality 

(Cordy and others, 2000).

Portion of the Colorado River 

Aqueduct in southern California
roundwater is a principal supply for domestic, industrial, and agricultural 

water in the Mimbres basin in southwestern New Mexico. Substantial 

groundwater withdrawals since the 1930s have resulted in water-table 

declines of as much as 40 m (130 ft), causing land subsidence, fissuring, and 

abandonment of some agricultural land. To better manage water resources in 

this area, it is critical to understand the quantity and movement of groundwater 

in the local aquifers. Partnering with the New Mexico Office of the State 

Engineer, the USGS set out to determine the shallow geologic structure of 

the Mimbres basin and to identify possible locations of other nearby productive 

aquifer systems. Previous studies indicated that the geologic structure of 

the basin is characterized by north- and northwest-trending subbasins, but 

the locations and depths of the subbasins were unknown. Sedimentation has 

filled and obscured the boundaries of these subbasins and formed potentially 

productive aquifers of varied thickness. As part of this study, the shape and 

depth of the subbasins were estimated from variations in the Earth’s gravity 

from one place to another. Differences in the density and thickness of sediment 

versus bedrock in these subbasins cause variations in gravity that are large 

enough to be measured. Analysis of the gravity data allowed for the separation 

of the regional gravity field from the gravity signal of the alluvium (sediment) 

filling the subbasins. The data were used to estimate the locations and depths 

of the subbasins and to compute the thickness of the alluvium. The thickness 

estimates were compared with exploratory drill-hole information, other 

geophysical data, and geologic mapping to check the accuracy of the gravity 

analysis. The resulting map of alluvium thicknesses indicated the existence 

of large areas of thin alluvium within the subbasins and suggested that there 

were no additional large, untapped aquifers in the area. The lack of additional 

groundwater for domestic, industrial, and agricultural demands highlighted 

the need to conserve current resources for future uses. For more information, 

see Heywood (2002).

Estimation of Aquifer Thickness in 

the Mimbres roundwater Basin, 

New Mexico, Using ravity

G 

G 

G 

. . . .facing the challenge
Basin boundary

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

EXPLANATION

Thickness, in meters

No estimate

0

50

100

200

300

400

500

600

700

800

900

1,000

1,100

1,200

1,300

2,200

0 10 20 30 40 KILOMETERS

0 10 20 30 40 MILES

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

4

108°00’ 107°30’

33°00’

32°30’

32°00’

Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 79

Estimated thickness of alluvial deposits in the Mimbres basin 

derived from gravity analysis. Modified from Heywood (2002).
80 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Rio Grande and Lower Rio Grande Valley—

Elephant Butte Reservoir to the Gulf of Mexico

The four subareas along the Rio Grande (subareas 5, 6, 7, 8; fig. 4–2) are located within

three physiographic provinces—Basin and Range, Great Plains, and Coastal Plain (fig. 2–2,

poster) (Fenneman, 1931; U.S. Geological Survey, 2003)—but are united by the Rio Grande. 

In these subareas, the river is the international boundary between Texas in the United States 

and Chihuahua, Coahuila, Nuevo León, and Tamaulipas in Mexico. The Rio Grande drains 

portions of the Chihuahuan Desert in southern New Mexico, northern Chihuahua, most of 

Coahuila, western Nuevo León, and southwestern Texas, as well as the subtropical lower 

Rio Grande valley of southern Texas and northern Tamaulipas. Mean annual flow was about

800 million m3 (650,000 acre-ft) for the period 1961–2006 below Caballo Dam about 161 

kilometers (100 miles) north of El Paso, Texas (U.S. Geological Survey, 2009). The primary 

tributaries are the Pecos River, Devils River, Rio Conchos, Rio San Rodrigo, Rio Salado, Rio 

Álamo, and Rio San Juan. Major aquifers are the Mesilla basin and Hueco bolson aquifers near 

El Paso, Tex., the Edwards-Trinity aquifer in south-central Texas, and the Gulf Coast aquifer in 

southeastern Texas. The Rio Grande has been described as a river that has been disconnected 

in the middle. Between Fort Quitman and Presidio, Tex., the river is intermittent, but near 

Presidio, the Rio Conchos, which drains 68,376 square kilometers (26,400 square miles) of the 

Sierra Madre Occidental of Mexico, provides substantial inflow that can contribute as much

as 75 percent of the downstream flow of the Rio Grande. The river then flows between Big

Bend National Park and adjacent protected areas in Mexico. Near its discharge to the Gulf of 

Mexico, flow in the Rio Grande is typically small, ranging from 0 to 25 m3 (0 to 872 cubic feet 

[ft3

]) per second from 1934 to 2008 (International Boundary and Water Commission, 2009), 

Rio Grande near Santana Mesa and flow may disappear prior to reaching the Gulf of Mexico.

Subareas 5, 6, 7, and 8.
Elephant Butte Reservoir

Amistad Reservoir

Pecos River

The portion of the Rio Grande in the Borderlands is highly 

regulated by four major reservoirs: Elephant Butte and Caballo 

Reservoirs in southern New Mexico and Amistad and Falcon 

Reservoirs along the Texas border with Mexico. These reservoirs 

were constructed for water storage and flood control and provide

a continuous source of water for irrigation that accounts for 

about 80 percent of surface-water use of Rio Grande waters on 

the United States side (Texas Natural Resource Conservation 

Commission, 1996). The 1906 Convention for Equitable 

Distribution of the Waters of the Rio Grande requires that the 

United States deliver about 77 million m3 (60,000 acre-ft) of 

irrigation water annually to Mexico as measured at El Paso–

Ciudad Juárez by way of the International Dam (Meuller, 

1975). Diversions carry water to crops in the floodplain of the

river, and numerous drainage ditches return agricultural runoff 

to the river, which has increased salinity. 

Pecos River Bridge

(tallest bridge in Texas)

Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 81
82 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Critical Issues

Growing human populations and natural climate variability are straining the water resources of the Borderlands. The 1944 

Treaty for Utilization of Waters of the Colorado and Tijuana Rivers and of the Rio Grande serves as the principal reference for 

boundary water questions between the United States and Mexico, but this treaty may not adequately address issues arising from 

the growing border population and increased competition for water resources (Southwest Center for Environmental Research 

and Policy, 2002). In Mexico, surface waters and groundwaters are considered a national resource and are federally regulated 

(Comisión Nacional del Agua, 2008). In the United States, regulation of the major rivers of the Borderlands, such as the Colorado 

River and the Rio Grande, has been decided by Supreme Court decisions, multistate compacts, and Congressional acts along 

with the international obligations described above. Groundwater resources, however, are not regulated by treaty between the 

United States and Mexico and, to varying degrees in the individual U.S. States, are less regulated than surface water.

Primary competing interests for available water resources include agricultural, industrial, 

municipal, and recreational uses. A number of animal and plant species on both sides of the 

border, many of them imperiled, also depend on an adequate supply of good-quality water 

(Fernandez and others, 2009; U.S Fish and Wildlife Service, 2011). Currently, a large share of 

water used for domestic and municipal supplies in the Borderlands is drawn from groundwater 

(Ward, 2003) at rates that often exceed the natural recharge of aquifers. Water tables have lowered 

as a result, which has caused land subsidence in a number of areas such as the Mimbres basin, the 

Imperial and Mexicali Valleys, and the Willcox and Douglas basins of southern Arizona (Arizona 

Land Subsidence Group, 2007). Subsidence and related earth fissuring can damage infrastructure

such as pipelines, canals, and roads. In aquifers pumped for agricultural, industrial, and 

municipal use, especially in the Mesilla basin and Hueco bolson, the salinity of aquifer water is 

increasing because deeper, more saline groundwater is intruding into the water supply (Witcher 

and others, 2004). Groundwater depletion throughout the Borderlands has caused several 

municipalities to pursue other water resources such as interbasin groundwater transfers, 

reallocation of traditionally agricultural supplies, and addition of surface-water supplies to 

meet municipal usage demands for drinking water and industrial use water. For example, 

while the City of Tucson uses Colorado River water delivered through the Central Arizona 

Project, it has also purchased agricultural land in a neighboring basin to supplement its 

groundwater resources and add to the city’s water supply. This change in the distribution of 

water supplies can complicate the existing issues of increasing endangered species and habitat 

requirements, water-rights claims, adjudication proceedings, and other legal issues.

Earth fissure in Cochise County, 

Arizona
Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 83

 Population growth and associated commercial growth in the Borderlands not only 

increase demand for available water supplies but also increase the possibility of contamination 

and degradation of water quality. The Tijuana River, for example, is one of the region’s 

largest contributors of chemical and microbial contamination to the Pacific Ocean (Gersberg

and others, 2004). In large agricultural areas such as the Mexicali and Imperial Valleys and the 

Rio Grande valley, pesticides and fertilizers degrade surface-water resources. Several streams 

in the Santa Cruz, San Pedro, Douglas, and Willcox basins of Arizona are designated as 

impaired because of Escherichia coli and nitrate exceedances (Arizona Department of 

Environmental Quality, 2008). In addition, there are widespread occurrences of metals and 

arsenic contamination in southern Arizona due in part to industry, current and historic mining, 

and natural ore deposits (Arizona Department of Environmental Quality, 2008; Arizona 

Department of Water Resources, 2009 a, b). Improper disposal of industrial chemicals, landfill

leachate, leaking underground storage tanks, and infiltration from septic tanks have affected

groundwater quality in municipal areas. Nearly 40 percent of wells in southern New Mexico 

have been found to be contaminated from a variety of human sources (Ward, 2003). 

In addition to contaminants, such as nitrates, pesticides, metals, and fecal bacteria, there is growing 

concern over pharmaceutical products that are commonly found in treated sewage and have 

been detected in the Rio Grande and many other river systems and aquifers in the Borderlands 

(Barnes and others, 2008; Focazio and others, 2008). Many compounds associated with these 

products are endocrine disrupters and possible carcinogens. Such organic contaminants have 

not been studied until recently, but published work to date indicates that they may be much 

more widespread than previously thought (Barnes and others, 2002; Barnes and others, 2008).

Increasing demands for surface-water and groundwater supplies and the increasing threat 

of contamination have led water-resource managers to consider alternative water resources. 

Some communities and government entities have implemented or are examining desalination 

of deeper saline groundwater to supplement their freshwater supplies. A joint project of 

El Paso Water Utilities and Fort Bliss created the world’s largest inland desalination facility, 

which produces 104 million liters (27.5 million gallons) of fresh water daily when running 

at full capacity. The facility turns brackish water from a formation underlying the freshwater 

zone within the Hueco bolson into a new freshwater source that supplements groundwater 

withdrawals from the Mesilla basin and Hueco bolson and surface water diversions from the 

Rio Grande. In addition, the diversion of the brackish water diminishes the upward intrusion 

of saltwater into the existing freshwater supply (El Paso Water Utilities, 2008). Though 

desalination plants augment freshwater supplies, they create new waste streams (concentrate) 

that must be disposed of properly to minimize any potential negative effect on the environment. 

El Paso Water Utilities uses deep wells to inject concentrate into receiving waters that have 

total dissolved solids concentrations that are greater than the concentrate. The interaction 

between vertically stacked aquifers, however, is generally not well understood, and withdrawals 

or injections into deeper aquifers have the potential to affect overlying and underlying aquifers.

Given the current stresses on water resources and the growing population in the Borderlands, 

resource planning requires timely and accurate science. The current stresses will only intensify 

with increased population and the predicted increase in drought and alteration of precipitation 

patterns that may occur with climate change (see chapter 10).

Tijuana River, Tijuana, Baja 

California

Yuma Desalting Plant, 

Yuma, Arizona
In many parts of the United States–Mexican border region, surface-water 

supplies are limited or nonexistent, so groundwater is an essential resource 

for human water needs. Groundwater discharging from aquifers also is critical 

for maintaining natural streams, springs, and riparian vegetation. Groundwater 

pumping removes water from storage in the aquifer, but with time, the effects 

of pumping spread to greater distances and can reduce groundwater discharge 

to natural features. The timing of these effects is dependent on aquifer properties 

and on the proximity of pumping locations to streams, springs, wetlands, and 

riparian vegetation. Extraordinary efforts have been carried out to better 

understand how groundwater pumping and artificial recharge by humans might 

affect the availability of groundwater to sustain streams, springs, and riparian 

vegetation. One of those efforts has been the development of a groundwater flow 

model simulating flow in the upper San Pedro basin of Arizona and Sonora that 

simulates movement of water from areas of natural replenishment (recharge) 

to areas of discharge. The model also can be used to understand the timing 

of the effects of pumping and artificial recharge on groundwater discharge to 

the San Pedro River in Arizona and Sonora and its congressionally protected 

riparian ecosystem, the San Pedro Riparian National Conservation Area. 

By running the model sequentially with a pumping well in a different location 

in each simulation, “capture maps” were constructed to illustrate effects on 

the river, springs, and vegetation for any pumping location. In the example 

capture maps shown, effects are given in terms of a fraction of the pumping 

rate, ranging from no effect (a fraction of 0.0, or 0 percent, in darkest blue) to 

an effect on resources equal to the total pumping rate (a fraction of 1.0, or 

100 percent, in red). The maps show the greatest effects of pumping near to 

the river, and comparison of the two maps shows that effects progress with 

time for most locations. The maps also can be used in the reverse sense to 

understand the timing of enhanced water availability to streams and vegetation 

by artificial recharge. Recharge in red areas would enhance water availability 

much more quickly than recharge in blue areas. For more information, see 

Leake and others (2008).

Capture Maps Help 

Water Managers Understand 

the Effects of roundwater Pumping 

on Streams, Springs, and 

Riparian Vegetation

G 

. . . .facing the challenge
ARIZONA

SONORA

Fort

Huachuca

Huachuca Mountains

 River

Babocomari 

 River

Babocomari 

San

Pedro

River

San

Pedro

River

Tombstone

Charleston Charleston

Palominas Bisbee

Sierra

Vista

Mountains

Mule

ARIZONA

SONORA

Fort

Huachuca

Huachuca Mountains

Tombstone

Palominas Bisbee

Sierra

Vista

Mountains

Mule

Fraction of Pumping Rate

Captured at 10 Years

Fraction of Pumping Rate

Captured at 50 Years

UNITED STATES

MEXICO

UNITED STATES

MEXICO

San Pedro Riparian

National Conservation Area

San Pedro Riparian

National Conservation Area

San Pedro Riparian

National Conservation Area

0 10 KILOMETERS 5

0 5 10 MILES

Less More

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 

Fraction of pumping rate

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

3

110°30’

31°45’

31°30’

31°45’

31°00’

110°15’

110°00’

110°30’

31°45’

31°30’

31°45’

31°00’

110°15’

110°00’

Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 85

Capture maps showing computed change in streamflow, riparian 

evapotranspiration, and springflow after 10 years (left) and 50 years 

(right) of continuous pumping or recharge in the upper San Pedro 

basin in Arizona and Sonora. The color at any location represents 

the fraction of the pumping/recharge rate by a well at that location 

that can be directly accounted for as a reduction/increase in 

availability of groundwater (respectively) for streams, springs, and 

riparian vegetation. Modified from Leake and others (2008).
 USGS Capabilities

A clear understanding of the quantity and quality of water along the United States–Mexican border is critical if it is to be 

used to support a thriving economy, intact ecosystems, and a growing, healthy population. Additional research and a combination 

of new and traditional tools are needed to fill gaps in our understanding of how these sectors act and interact with regard

to water. By using existing approaches, developing new techniques and tools, and bringing together scientists from diverse 

disciplines such as ecology, geology, geography, social science, and hydrology, the USGS is prepared to address the complex 

questions presented by the interactions of people, land, ecosystems, climate, and water along the United States–Mexican border. 

The capabilities of the USGS (table 4–1) allow us to monitor, characterize, and model hydrologic processes and thus assess 

water supplies and water quality and address water-resource issues in the Borderlands. In recent years, our ability to monitor and 

store data has improved tremendously. We can follow trends in groundwater levels, river flow, and water quality with greater

resolution and in more places than ever before with greater accuracy and precision. Scientists with the USGS now monitor, via 

satellites, changes in land use, land cover, and water storage in river basins at a space and time resolution heretofore impossible. 

We can see underground in three dimensions using a variety of geophysical tools and can thus understand the shapes and boundaries 

of aquifers and the distribution of geologic materials within them. With newly developed regression equations, we can now 

predict flow in ungaged basins. We can then take the data generated by these monitoring techniques and combine them in multiparameter models to understand and predict how land-use change, topography, population growth, changes in agricultural practices, 

urban expansion, and climate change affect flow in rivers, groundwater levels, and sediment and contaminant movement.

U.S. Geological Survey employee

collecting a water quality sample

in response to Hurricane Irene,

August 2010.
Water quality sampler used by the U.S. Geological Survey

The USGS Water Resources National Research Program (http://water.usgs.gov/nrp/) 

develops new methods, theories, and techniques to understand, anticipate, and solve waterresource problems. Scientists with the USGS work closely with colleagues in other Federal 

agencies, State water agencies, and State Water Resource Research Institutes to help plan, 

facilitate, and conduct research to aid in the resolution of State and regional water problems. 

We are also building strong relationships with scientists and agencies in Mexico. Through 

formal partnerships, the entire suite of USGS capabilities can be called on to assist land- and 

water-resource managers at all levels of government. Below are some examples of USGS 

programs that provide unique resources to help address complex hydrologic problems. 

The USGS operates and maintains approximately 7,500 streamgages as part of the 

National Streamflow Information Program and the Cooperative Water Program, which provide

long-term, accurate, unbiased, and permanently archived streamflow data (http://waterdata.

usgs.gov/nwis) to meet the needs of diverse users (Norris, 2001). Streamflow data are not only

essential in assessing water availability, but are also a critical component of the flash flood and

debris-flow warning system provided by the U.S. Geological Survey and the National Oceanic

and Atmospheric Administration. Some of the oldest gages in the national network are especially 

relevant to the United States–Mexican border region; for example, the Rio Grande gages at 

Embudo, N. Mex., and below Elephant Butte Dam have records dating back to 1889 and 1917, 

respectively. These long-term records are essential if we are to understand and predict flood

frequency, monitor climate change, and assist the U.S. Army Corps of Engineers as well as city 

and State governments in assessing infrastructure needs and zoning requirements for floodplain

and disaster management. The majority of gages are funded through partnerships involving the 

USGS, Indian tribes, and Federal, State, and local agencies with a need for streamflow data.

In groundwater studies, the USGS is at the forefront of devising new techniques and tools, 

such as surface and borehole geophysical applications and chemical and isotopic age-dating 

methods, that provide detailed understanding of flow paths, water-rock interactions, recharge

processes, and other aquifer characteristics. Current USGS research is focused on integrating 

surface, borehole, and airborne geophysical data analyses in order to image subsurface geologic 

structure, estimate physical properties that control fluid flow and contaminant transport, detect

contaminants, and monitor hydrologic and remediation processes.
Table 4–1. U.S. Geological Survey Water Resources capabilities for examining hydrologic systems.

Discipline Capabilities

Water Chemistry—Assess natural and contaminant chemicals 

in water and sediment, and study fundamental chemical and 

biochemical processes that affect the movement of organic 

and inorganic solutes in aquatic systems. 

Organics in aquatic systems 

Carbon cycling

Isotope hydrology and paleohydrology 

Trace elements and radionuclides 

Weathering and watershed processes 

Transport and biogeochemical reactions 

Gases in aquatic systems 

Groundwater Hydrology—Understand the processes that control 

movement and availability of subsurface water; its transport 

of dissolved substances, microbes, particulate, and other fluid

phases; and its interactions with the geological environment.

Development and application of quantitative groundwater models

Groundwater resource assessments

Groundwater–surface water–atmospheric interactions

Unsaturated-zone hydrology

Fractured-rock hydrology

Groundwater in geologic processes

Geophysical investigation of subsurface processes

Surface-Water Hydrology—Quantify, understand, and model 

the physical processes that control the distribution and quality 

of the Nation’s surface-water resources.

National stream gaging network

Flow and transport in rivers

Watershed modeling

Estuarine hydrodynamics

Climate variability and surface-water hydrology

Statistical analysis of floods and droughts

Hydrogeologic Framework Modeling Geologic mapping

Three-dimensional modeling

Geophysical data integration

Hydrostratigraphy

Geomorphology and Sediment Transport—Understand 

stream-channel morphology and erosional processes that 

govern the source, mobility, and deposition of sediment.

Sediment transport dynamics

Changes in river channels over time

Channel morphology and sediment transport

Flow and sediment mechanics

Ecology—Investigate the ecological and biogeochemical processes 

that affect the quality of water in aquatic systems.

Microbiology

Aquatic ecology

Climate and ecology

Biogeochemistry

88 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 89

The state-of-the-art National Water Quality Laboratory (NWQL) analyzes water, sediment, 

soil, and plant and animal tissue for constituents such as heavy metals, pesticides, polychlorinated 

biphenyls (PCBs), and flame retardants, as well as components of pharmaceutical and personal-care

products such as hormones, barbiturates, antimicrobial compounds, and anti-epileptics. The 

NWQL provides high-quality, reproducible water-quality data to the Nation, readily accessible 

on the Internet (http://nwql.usgs.gov/). The laboratory specializes in trace- and ultratrace-level 

analyses and the identification and quantification of benthic invertebrates. These analytical

facilities and their leading-edge capabilities, especially for research on emerging contaminants, 

are ideal for the characterization of a wide range of contaminant sources and allow the USGS 

to conduct research on topics such as the effects of sewage treatment and disposal on groundwater 

and surface-water quality along the border. Other specialized laboratories around the country 

expand and deepen USGS investigative capabilities: the Chlorofluorocarbon Laboratory in

Reston, Virginia, can date young waters through chlorofluorocarbon, sulfur hexafluoride, and

tritium-helium methods; the Wisconsin mercury laboratory is pioneering the detection of highly 

toxic methylmercury at ultratrace levels; and the Stable Isotope Laboratories, also in Reston, 

use isotope ratio techniques to identify sources of waters, flow paths in aquifers, and the migration

of contaminants.

Computer models allow us to conduct hydrologic experiments that would be too costly 

or lengthy to carry out any other way. Computer models can incorporate all measured and 

monitored information collected in rivers and aquifers and couple it with the best mathematical 

and theoretical understanding of the manner in which the physics, chemistry, and biology of 

a system fit together and interact. By comparing the output of computer models to measured

data, calibrated models give us an idea of how well we understand the complex interplay 

among processes such as pumping or contaminant movement in rivers and aquifers. The USGS 

has built extensive modeling capabilities through the development of hydrologic software such 

as GCLAS (constituent loading in surface waters), HYDROTHERM (multi-phase groundwater 

and heat transport), PHAST (flow, solute transport, and geochemical reactions), PHREEQC

(geochemical analyses), and MODFLOW, many of which have become industry standards.1

For instance, MODFLOW is the mostly widely used groundwater-modeling software in the 

world. State and local governments, groundwater scientists, and engineers in the private sector 

often need predictive computer models to make informed decisions on hydrologic resources. 

Models are developed by the USGS for use in the public interest and the advancement of science, 

and their developers are continually improving the capabilities of the models to better simulate 

physical, chemical, and microbial processes.

It is expected that water challenges along the United States–Mexican border will continue 

into the foreseeable future. With population increases, urbanization, and the growing effects 

of climate change, there will continue to be issues of water sufficiency and contamination in

this arid region. The USGS will continue to fulfill its role by providing the scientific and

technical information needed to support communities, decisionmakers, and resource managers 

in their efforts to ensure a sufficient supply of good-quality water for the people and

ecosystems of the Borderlands.

References cited in this chapter are listed in chapter 12.

1

 GCLAS, Graphical Constituent Loading Analysis System; PHAST, combination of PHREEQC and HST3D; 

MODFLOW, modular three-dimensional finite-difference groundwater flow model.
Population growth and agricultural and industrial development along the 

Rio Grande, particularly along the part of the river that forms the international 

boundary between Texas and Mexico, have altered the water quality and flow of 

the river. Urban and agricultural runoff and wastewater discharges from industrial 

and municipal facilities are potential sources of toxic organic compounds such 

as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), 

and organochlorine pesticides including DDT (dichlorodiphenyltrichloroethane) 

and chlordane that were banned earlier in the United States than in Mexico. 

The USGS has used semipermeable membrane devices (SPMDs; Alvarez, 2010) 

as long-term contaminant-accumulating samplers to detect concentrations of 

hydrophobic organic compounds in the lower reach of the Rio Grande. 

Traditional monitoring of PAHs, PCBs, and pesticides typically emphasizes the 

collection and analysis of riverbed sediments and the tissues of aquatic 

organisms because many of these compounds stick to sediment surfaces and 

move into the fat of people and other organisms. Traditional water-sampling 

methods generally involve a single grab or a representative composite sample 

that is taken during a few seconds or minutes. The short duration of traditional 

water-sampling methods and the small volumes of water collected decrease the 

probability that hydrophobic contaminants can be detected if they are present at 

low or variable levels. An SPMD typically consists of a lipid film membrane with a 

high surface-area-to-volume ratio and is similar to a biological membrane such 

as a fish gill. The SPMDs were deployed in the Rio Grande in 1997 for about 

30 days at six locations between Presidio and Brownsville, Tex. Seven 

organochlorine pesticides, including DDT and its daughter product DDE 

(dichlorodiphenyldichloroethylene), were detected in these SPMDs. All 

organochlorine pesticides detected were banned or restricted from use in the 

United States by the U.S. Environmental Protection Agency in the 1970s or 1980s 

and by Mexico in the late 1990s. Frequent detections of these compounds 

demonstrated their persistence in the aquatic environment and the continuing 

need to monitor for legacy contaminants that might remain in the environment for 

decades after release or that might be less regulated in certain countries.

The Use of Semipermeable 

Membrane Devices To Assess 

Organic Compounds in the 

Rio rande from Presidio to 

Brownsville, Texas

G 

. . . .facing the challenge
Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century 91

U.S. Geological Survey employees prepare a semipermeable 

membrane device (SPMD) for deployment (top and bottom 

right). The membrane, housed in a deployment capsule (above), 

is similar to biological membranes and thus can simulate the 

bioaccumulation of organic compounds in water and sediment.
Challenge Theme 3.

Protecting the Environment and 

Safeguarding Human Health

By Diana M. Papoulias and Jean W. Parcher

Introduction

Many of the diverse, fragile ecosystems of the United States–

Mexican border region are reaching unsustainable levels because of 

rapid population growth and changes in land use. Water shortages 

and pollution, poor air quality, increased soil salinities, and pesticides 

and heavy metal contaminants are some of the many stressors that are 

degrading the quality of life in the Borderlands. Lack of water treatment 

and wastewater infrastructure on both sides of the United States–

Mexican border contributes to elevated rates of various communicable 

diseases most commonly found in developing countries: tuberculosis, 

intestinal infections, and hepatitis. Chronic diseases (diabetes, cancer, 

and heart disease) also prevail at high rates along the border, resembling 

trends observed in developed countries. In addition, the subtropical 

climate of the Borderlands is particularly suited for vectors of tropical 

diseases, such as malaria and dengue fever.

Chapter 5
Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 93

Health problems caused by zoonotic and emerging infectious 

diseases as well as from environmental contamination are predicted to 

increase significantly along the United States–Mexican border in the 

years ahead. As human populations increase and urban areas expand 

along the border, the potential for more frequent interaction between 

humans and wildlife increases, which in turn increases the possibility of 

disease transmission between wildlife and humans. Since international 

borders are not barriers to disease migration, coordination among 

United States and Mexican health officials concerning global epidemics, 

such as avian influenza (bird flu), can be of great importance in 

controlling the spread of diseases.
94 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Issues—Environmental Stressors

Agriculture

Plentiful land, subsidized irrigation, and access to laborers made farming and ranching 

prosperous pursuits in the U.S. border states during the second half of the 20th century. 

Agriculture remains an important economic force, but it also can act as a stressor on the 

environment. Agriculture affects the environment and human health in the Borderlands through 

pesticide use, chemical and fecal contamination of surface water and groundwater, dewatering 

of habitats, salinization of soils on irrigated lands, and habitat fragmentation (Eswaran and 

Dumanski, 1994; Eswaran and others, 2001). In the warmer climates of the Borderlands where 

population is increasing, the competing demands for water are causing local water managers 

to rezone farmland for other uses, but production of cotton, vegetable crops, melons, citrus, 

and pecans is still common from the Imperial Valley in California, through Yuma, Arizona, to 

the lower Rio Grande valley in Texas. More people are living in proximity to agricultural areas 

now than in previous decades. 
Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 95

Lack of Infrastructure

In Texas alone, more than 1,800 rural communities, known as colonias, lack adequate sewer and water infrastructure, 

proper roadways, or structurally sound housing (Parcher and Humberson, 2007) (fig. 5–1; see also chapter 6). Commonly, dwellings

in colonias are constructed in ephemeral stream channels (arroyos or washes), and when water flows through these channels,

especially during summer monsoons, it carries refuse and human waste from the colonias downstream, often into adjacent cities. 

In many border cities, the storm-sewer infrastructure is outdated and lacks required capacity. Consequently, during heavy rains, 

flooded residential areas do not drain properly; stagnant water can remain for weeks, creating areas for mosquitoes to breed and

increasing the opportunity for transmission of water-borne diseases. In the Ambos Nogales watershed—the sister city area of 

Nogales, Arizona, and Nogales, Sonora—summer flooding has caused ruptures in sewer pipelines. The mayors on both sides

of the border are working to manage this problem so as to avoid contaminating the local Santa Cruz River, the main source of 

water for the area.

Figure 5–1. Many colonias 

along the United States–

Mexican border often have 

substandard housing and lack 

critical infrastructure such as 

potable water, adequate sewer 

systems, proper drainage, and 

paved roads. 
96 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
Figure 5–2 (facing page). Increased traffic across the United 

States–Mexican border, especially trade-related traffic, has led to 

the accumulation of several waste tire piles in the border region 

(bottom). The U.S. Geological Survey has been able to locate 

waste tire sites through orthodigital photography (top).

A line of trucks waiting at the border crossing leaving Tijuana, 

Baja California

Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 97

Transportation

Currently, Mexico is the second largest trading partner of the United States, after Canada. Trade between the United States 

and Mexico has soared over the past decade since the North American Free Trade Agreement (NAFTA) went into effect in 1994. 

In 2000, the value of trade had increased by 17 percent per year since 1995 and was projected to continue to grow at about 

5.9 percent per year (Jannol and others, 2003). Trade between the United States and Mexico reached $347 billion in 2007. 

Goods predominantly move across the border on trucks, which pass through 39 ports of entry between the Pacific Ocean and the

Gulf of Mexico. The current border-crossing infrastructure was not designed to handle the large traffic volumes that have developed

since NAFTA, so international trade-related traffic destined for the interior of the United States or Mexico increasingly uses local

transportation systems, many of them urban. This large amount of vehicles not only causes problems such as air pollution from 

idling cars and trucks waiting to pass immigration inspection, but also contributes to the accumulation of waste tires (fig. 5–2),

the prevalence of oil and gasoline storage facilities, and increased transport of hazardous waste.
Uranium ore

Kelly mine, Socorro County, 

New Mexico, 1916

98 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Industry

Foreign-owned manufacturing and assembly plants (maquiladoras) along the Mexican 

side of the border are an important source of employment, but many of these industrial sites 

are associated with negative effects on the environment. In 2007, more than one thousand 

industrial plants were estimated to be operating in the Mexican border states (Instituto Nacional 

de Estadística y Geografía, 2007). In addition to these facilities, more traditional sectors, such 

as petroleum refining and steel manufacturing, are also present in both countries. Despite laws

on both sides of the border that regulate these industries, issues such as chemical production; 

pollutant discharge to air and surface waters; and the generation, transportation, storage, treatment, 

and inadvertent release of hazardous wastes contribute to environmental degradation (Good 

Neighbor Environmental Board, 2003, 2004; Anderson and Gerber, 2007).

Energy and Mining

Northern Mexico and southern Texas have abundant energy resources including coal, 

coal bed methane gas, oil, and natural gas. The exploration, production, and transport of fossil 

fuels to provide for energy needs in both countries are expected to continue to grow into the 

near future (U.S. Energy Information Administration, 2010), and new infrastructure, such as 

power plants, coastal liquefied natural gas terminals, and wind turbine farms both on and off

shore, will be needed. 

Abandoned legacy mine lands dating from the Spanish colonial period to modern mines 

(to a lesser extent)—mining mostly porphyry copper–molybdenum, some gold, and other 

minerals—are sources of toxicants to land and water. For example, uranium ore has been 

mined along the Gulf Coast of south Texas (Finch, 1996), but continued mining of this resource 

threatens to affect air and water quality in the region. Activities of the energy and mining 

sectors may contribute to habitat destruction, water pollution, contaminated surficial soils,

and poor air quality (Hester and Harrison, 1994). 

See also chapter 7.
Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 99
Big Bend National Park (BBNP) covers 324,231 hectares (801,163 acres) 

along a 190-kilometer (118-mile) stretch of the Rio Grande at the United States 

border with Mexico. The park is situated in the Chihuahuan Desert, an 

ecosystem known for its beautiful mountain and basin environments and 

extraordinary biological diversity of native plants and animals. The park is 

home to more than 1,200 species of plants and more than 450 species of birds, 

56 species of reptiles, and 75 species of mammals. Mineral deposits bearing 

mercury, uranium, and fluorite have been found in BBNP, but of these, only 

mercury has been mined significantly. No mercury mines currently are 

operating in the area, but past total mercury production ranks the Terlingua 

district as the third largest mercury mining region in the United States. 

Mercury is highly concentrated around the abandoned mines, and water 

draining the mines enters streams in the local ecosystems. The effect of 

runoff from mines located inside and just outside the park boundary is a 

concern for both wildlife and humans. The USGS has been measuring 

mercury concentrations in mine waste, sediment, water, and air throughout 

BBNP to address potential mercury contamination around these mercury 

mines. Results of the USGS research (Gray and others, 2006) show that total 

mercury concentrations decrease in sediment collected more than 1 kilometer 

from the mine and are below the mercury concentration at which harmful 

effects are likely in sediment-dwelling organisms. Although mercury 

concentrations were elevated in mine waste, the concentrations of 

methylmercury were generally low in the ecosystems downstream because 

conditions for transformation to methylmercury are unfavorable in this hot 

and dry desert climate.

Mercury Contamination in 

Big Bend National Park, Texas

. . . .facing the challenge
cinnabar

Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 101

Stream sediments collected downstream from the Mariscal mine (bottom) in Big Bend National Park, Texas, showed rapid dispersion of 

total mercury and methylmercury (Gray and others, 2006). Mercury, such as contained in the cinnabar (mercury sulfide) sample shown 

(top), is no longer actively mined in the park, but mine waste can still contaminate the local ecosystems. 
102 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Status—Effects of Environmental Stressors

Air Quality

Large, industrial sister cities along the United States–Mexican border (San Diego–Tijuana, El Paso–Ciudad Juárez, and 

Laredo–Nuevo Laredo) fall short in meeting air quality standards (Naumann, 2004). The air pollution is contributing to human 

health problems and the loss of visual aesthetics (Sweedler, 2003). Emissions from cars, trucks, factories, and power plants and 

the burning of trash, especially tires, are the main sources of air pollution in the Borderlands (Sweedler, 2003; Good Neighbor 

Environmental Board, 2006). 

A combination of high winds generated along dry/moist pressure gradients and abundant dust sources, including playas and 

dune fields, create dust storms; major storms occur almost annually in the Chihuahuan Desert area of Texas, New Mexico, and

Chihuahua (T.E. Gill, Texas Tech University, written commun., 2004). In addition, the dry landscape, made up of agricultural 

fields, mine lands, and unpaved roads, is a constant source of airborne dust and particulates that contribute to the exposure of

humans to potentially toxic heavy-metal and organic contaminants, pathogens, and allergens. The U.S. Environmental Protection 

Agency (EPA) has identified dust, sulfur dioxide, nitrogen dioxide, ground-level ozone, carbon monoxide, polycyclic aromatic

hydrocarbons (PAHs), and mercury among the damaging pollutants affecting air quality along the United States–Mexican border 

(Currey and others, 2005; U.S. Environmental Protection Agency, 2011b).
2:40:06 pm

2:40:08 pm

2:40:11 pm

2:40:14 pm

Time-lapse photos recording 8 seconds during a dust storm along 

south-bound Interstate 5 in southern California

Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 103
As part of the USGS Biomonitoring of Environmental Status and Trends 

program for the Rio Grande basin, contaminant stressors for the flora and 

fauna in the region were assessed. One product of the assessment was a 

geo-referenced contaminants-in-biota database of tissue residue information 

for aquatic and riparian species, collected from an extensive literature review 

(Mora and Wainwright, 1998). The assessment of the exposure of aquatic 

organisms to contaminants allows for the identification of those environmental 

contaminants to which humans and wildlife may be exposed. When combined 

with other data layers, public health professionals and natural resource 

managers can use this database to investigate relations between contaminants 

and potential sources (anthropogenic, geologic, etc.), map exposure routes, 

and indicate vulnerable communities or ecosystems.

eo-Referenced Database of 

Contaminants in Biota 

Blue crab (Callinectes sapidus)

Greater earless lizard

(Cophosaurus texanus )

Channel catfish (Ictalurus punctatus)

G

. . . .facing the challenge
Río Bravo

Rancho Viejo

Matamoros

El Control–

Ramírez

Bayview

Nuevo Progreso

Port Isabel

Lyford

Donna

Gustavo

Díaz Ordaz

Alamo

Edinburg

Brownsville

Reynosa

Raymondville

McAllen

South Padre

Island

Alton

Sullivan City

La Feria

Santa Rosa

Rangerville

TEXAS

TAMAULIPAS

UNITED STATES 

MEXICO

RIO GRANDE

RIO BRAVO

Gulf of Mexico

98°30’ 98°15’ 98°00’ 97°45’ 97°30’ 97°15’

26°45’

26°30’

26°15’

26°00’

0 6 12 18 24 KILOMETERS

0 6 12 18 24 MILES

EXPLANATION

Contaminants in biota

Bird

Fish

Herp

Invertebrate

Mammal

Sediment

Soil

Water

International boundary

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

8

Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 105

Presence of contaminants in biota along

the United States–Mexican border in the 

lower Rio Grande valley. Data from U.S. 

Geological Survey Border Environmental 

Health Initiative, Environmental Contaminants 

in Biota database (http://borderhealth.cr.usgs.

gov/datalayers.html ). 

Great blue heron (Ardea herodias )
106 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Water Quality

Agricultural practices on both sides of the border have led to pesticide contamination in 

lakes and rivers through agricultural runoff, as well as water contaminated by the elements 

selenium, manganese, aluminum, iron, zinc, and copper (Mora and Wainwright, 1998). Other

sectors (industry and mining) might contribute to water contamination through the dispersion 

of cadmium, lead, cyanide, arsenic, mercury, PAHs, polychlorinated biphenyls (PCBs), and 

solvents from point and nonpoint terrestrial sources and aerial deposition. For example, 

heavy-metal concentrations from human sources in the San Pedro River of Sonora and Arizona 

exceed sediment-quality criteria (Gómez-Álvarez and others, 2007). Lack of proper or 

sufficient sewage and storm-water treatment facilities can also lead to water contamination,

such as in the microbial contamination of potable and recreational waters in the Rio Grande 

(Texas Clean Rivers Program, 2009). 

For many border communities, the Rio Grande is the only source of water for drinking, 

bathing, cooking, and washing clothes and dishes. Significant portions of the Rio Grande,

however, do not meet standards for aquatic life and contact recreation uses, in large part 

because of the large amount of untreated wastewater and runoff that is discharged into the 

Rio Grande from both urban and rural communities, compounded by the limited flow and

availability of water (Texas Clean Rivers Program, 2008). Conditions are equally poor in 

the western part of the Borderlands, where only recently the construction of new wastewater 

treatment plants has provided proper treatment for some of the millions of gallons of raw or 

undertreated sewage that flowed through California’s New River (U.S. Environmental Protection

Agency, 2011a) and Tijuana River. Nevertheless, the need to treat wastewater continues 

to exceed infrastructure capacity in much of the Borderlands (Briggs, 2007; Morales, 2007). 

See also chapter 4.

Nogales International 

Wastewater Treatment Plant

South Bay International 

Wastewater Treatment Plant

Nuevo Laredo International 

Wastewater Treatment Plant
New River crossing the border 

into California

(Below) Sewer pipe being 

installed near the United 

States–Mexican border

Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 107
In the United States, the Safe Drinking Water Act requires that each 

State prepare a source water assessment of public water supplies. In 

cooperation with the Texas Commission on Environmental Quality, the USGS 

collected and geo-referenced more than 65,000 potential sources of 

contaminants (PSOCs) to groundwater supplies in Texas including landfills, 

waste piles, hazardous waste disposal sites, waste injection wells, oil and 

gas wells, and certain types of businesses. Because Mexican data gathered 

for this purpose are lacking, PSOCs in Mexico were interpreted from the 

most current Instituto Nacional de Estadística y Geografía (INEGI) vector and 

geographic names (topónimos) data. The United States and Mexican datasets 

were merged and then clipped along the binational watershed boundary for 

inclusion in the BEHI project. The dataset currently is limited to the border 

region between Texas to the north and Tamaulipas and Nuevo León to the 

south, but digital cartography information from the INEGI is being used to 

expand the dataset to include the adjoining Mexican states.

Potential Sources of Contaminants 

in the Lower Rio Grande Valley

. . . .facing the challenge
Río Bravo

Rancho Viejo

Matamoros

El Control–

Ramírez

Bayview

Nuevo Progreso

Port Isabel

Lyford

Gustavo

Díaz Ordaz

Edinburg

Brownsville

Reynosa

Raymondville

South Padre

Island

Alton Sullivan

City

Rangerville

TEXAS

TAMAULIPAS

UNITED STATES 

MEXICO

RIO GRANDE

RIO BRAVO

Gulf of Mexico

98°30’ 98°15’ 98°00’ 97°45’ 97°30’ 97°15’

26°45’

26°30’

26°15’

26°00’

0 6 12 18 24 KILOMETERS

0 6 12 18 24 MILES

EXPLANATION

Potential source of contaminants

Cemetary

Gun range

Business

Transportation

Waste

Wastewater

International boundary

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

8

Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 109

Potential sources of contaminants 

in eastern Texas along the United 

States–Mexican border. Data from 

U.S. Geological Survey Border 

Environmental Health Initiative, 

Potential Contaminants database 

(http://borderhealth.cr.usgs.gov/

datalayers.html ).
110 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Soil and Sediment Quality

Although air and water quality are of greatest concern with respect to environmental and 

human health throughout the Borderlands, contaminated soils and sediment are of concern in 

many places in the border region. Salt is present in all irrigation water, so its concentrations 

in irrigated soils increase over time, left behind after applied water evaporates from the 

surface or is transpired by plants. Soil salinization as a result of irrigation practices 

continuously increases in arid lands and, unless managed appropriately, eventually 

the land can no longer support life. Poor agricultural practices, among other causes, 

can also contribute to increased sedimentation in reservoirs and rivers, and 

sediments can choke and fill streams and wetlands, leading to stagnation and

buildup of toxic contaminants. It is estimated that the storage capacity of the 

Amistad-Falcon reservoir system on the lower Rio Grande will be reduced 3.5 

percent by 2060 given current sedimentation rates (Texas Water Development 

Board, 2005). Another effect of poor soil quality is the presence of Valley Fever, 

a common debilitating fungal disease caused by the microbe Coccidioides immitis

and carried in windborne arid soils (Bultman and others, 2004; see also 

http://health.usgs.gov/inhalation/valley_fever.html). The rate of Valley Fever has 

tripled from 1999 to 2007 in Arizona, including those counties on the border (Arizona 

Department of Health Services, 2008). 

One consequence of the maquiladora phenomenon over the last four decades is the 

accumulation of and increased exposure to industrial hazardous waste. Hazardous waste is 

dumped illegally just outside city limits, often in desert habitats; neighborhoods and communities 

are exposed to abandoned waste sites or industrial facilities; and hazardous waste from major 

industries is transported to municipal landfills, some which may not have the ability to safely

store such waste. For example, unhealthy levels of arsenic and lead have been found in soils 

and sediments around a mine smelter in El Paso, Tex. (Ketterer, 2006).

Populations at Risk

The sectors of the human population most likely to exhibit poor health as a result of 

environmental degradation along the border are the young, the elderly, and pregnant women. 

Wildlife is also exposed to the same environmental stressors and in some cases even shares 

pathogens with humans. Air pollution puts the elderly and children, especially, at risk for 

respiratory diseases, irritated eyes, alterations in the body’s defense systems against foreign 

materials, damage to lung tissue, carcinogenesis, and premature death. In 2004, the 

nonprofit organization Clear the Air projected that the total deaths attributable to power

plants in California in 2010 would be 249, with related hospital admissions at 195; for Texas, 

the deaths were estimated at 1,160 and the hospital admissions at 1,105 (Schneider, 2004). 

Infectious diseases, particularly those associated with water such as gastrointestinal diseases 

and hepatitis A, are more prevalent in the Borderlands population than in the general U.S. 

population. In 2002, the rate of hepatitis A was 12.10 cases per 100,000 Hispanic children in 

San Diego County, compared to about 5.0 for all children nationally (Weinberg and others, 

2004; Wasley and others, 2008). Mosquitoes carrying West Nile virus and dengue fever are of 

concern in the lower Rio Grande valley. The USGS is aiding public health officials by

developing methods to identify areas of high soil moisture and therefore potentially stagnant 

water, which can be potential mosquito breeding grounds (Hubbard and others, 2008).

Lupus rates in Nogales, Ariz., (94 cases per 100,000 inhabitants) have been reported to 

be higher than the highest published rates recorded in medical literature (Balluz and others, 

2001). This auto-immune disease is believed to be linked to environmental causes and in 

Nogales, Ariz., may be related to environmental contaminants (Balluz and others, 2001). 

Studies done in partnership with the Centers for Disease Control and Prevention have also 

noted suspected clusters of multiple sclerosis cases near a smelter in El Paso, Tex., (http://www.

dshs.state.tx.us/epitox/mspilot.shtm) and childhood leukemia cases near a military installation 

at Sierra Vista, Ariz. (http://www.cdc.gov/nceh/clusters/sierravista/). 

Sputum culture of

Coccidioides immitis
mosquitoes

Exposure to environmental contaminants or pathogens can put stress on wildlife in the Borderlands already stressed by habitat 

loss, potentially making them more susceptible than unstressed populations to the health effects of toxins and disease-causing 

organisms. The health status of fish and wildlife species is detected through Federal monitoring programs, and the causes for

poor health are investigated through laboratory and field studies. In this way, a wide range of contaminant-related wildlife health

cases have been documented. Some migratory birds and predatory raptors show elevated levels of metals, organochlorine, and 

organophosphate pesticides, which affect reproduction (Mora, 2003; Mora and others, 2007), and similar chemical compounds 

at levels that exceed toxicity thresholds have been found in the tissues of fish from the Rio Grande, with biomarkers suggesting

effects on their reproductive systems (Schmitt and others, 2005). The consumption of water contaminated by mine waste can 

also poison birds and other wildlife. Fish in some areas of the lower Rio Grande valley are contaminated with mercury and 

organochlorine pesticides to such an extent that the Texas Parks and Wildlife Department has issued human consumption advisories 

(Texas Parks and Wildlife, 2012). To the east, encephalopathic chronic wasting disease in white tail deer has just recently arrived 

at the Chihuahuan border from the north—it is unknown how this new disease will affect already stressed populations.

Mosquitoes can transmit 

diseases such as West Nile virus 

and dengue fever. Prevention 

includes managing populations 

of live carriers (for example, 

Aedes albopictus, left) and 

identifying areas of standing 

water that serve as breeding 

grounds (top, Culex sp. larvae).
Most chemical compounds released into the air and soil are eventually 

found in surface water and groundwater. Those compounds with chemical 

properties that make them difficult to breakdown can adsorb to sediment 

particles and be deposited on the bottom of a lake or at the mouth of a river. 

Over time, as sediments accumulate, a record of chemical inputs to the 

environment can be detected in the layers of sediment. The Texas Water 

Resources Center, through the USGS National Water-Quality Assessment 

Program, and State partners have been collecting data from sediment cores 

from a number of surface waterbodies associated with the Rio Grande basin in 

south Texas (Van Metre and others, 1997; Mahler and Van Metre, 2002). The 

results have facilitated an analysis of temporal trends and the identification

of contaminant sources. Data have also been useful in water quality and 

risk assessment.

For example, in 1993, the EPA discovered high concentrations of PCBs in 

Donna Canal, an 11-kilometer (6.8-mile) canal flowing north from the Rio Grande 

to Donna Reservoir in Hidalgo County, Tex. In an attempt to determine the 

source of the contaminant, the USGS made five sampling trips to Donna Canal 

from February 1999 to April 2001, with the results of each trip narrowing the 

sampling area for the next trip (Mahler and others, 2002). The results of the 

sampling identified a 600-meter (1,969-foot) reach as the likely source, 

allowing the Texas Natural Resource Conservation Commission (now the 

Texas Commission on Environmental Quality) to focus their assessment and 

remediation efforts.

Sediment Cores as a Record of 

Environmental Contamination along 

the Rio rande

Example of a sediment core 

ready to be sliced for analysis.

G

. . . .facing the challenge
Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 113
114 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

 USGS Capabilities

The USGS can provide valuable resources in database development and geospatial analysis in both the human and 

environmental health fields to State, local, and binational commissions with responsibility for ensuring health and quality of life

in the Borderlands. Within all the disciplines, USGS expert modelers work with others to develop the scientific tools to support

management of our Nation’s natural resources and help protect lives and property. Scientists with the USGS involved in the 

Border Environmental Health Initiative project (BEHI; http://borderhealth.cr.usgs.gov) are working to facilitate compatibility 

and comparability between United States and Mexican databases on census information, health statistics, water quality, and 

contaminants to allow more rigorous transborder analyses of human health issues.

A number of Federal, State, and academic institutions are actively involved in addressing the effects of agriculture, and the 

USGS historically has supported these activities by providing long-term water quality monitoring, data modeling, and land cover 

and land use mapping. An expanded USGS role would provide leadership in the interpretation of water quality data relative to 

human and wildlife health, more extensive real-time surface water and groundwater monitoring information, long-term 

monitoring of biota for contaminant exposure and effects, aerial photography to enable the study of landscape conditions 

through remote-sensing analysis, and the studies needed to define transboundary groundwater resources and their interaction

with surface waters. Currently, the USGS is leading a team to build a binational water quality database in southern Texas.
Challenge Theme 3. Protecting the Environment and Safeguarding Human Health 115

The USGS also has the opportunity to collaboratively develop systematic approaches for identifying and characterizing 

hazardous waste dump sites on both sides of the border. In the field of hazardous waste site monitoring and measurement, scientists

with the USGS have developed new approaches and technologies to substantially improve the cost-effectiveness of site 

characterization. The collection, processing, and analysis of remote sensing data could be used to identify, assess, and monitor 

hazardous waste disposal sites and their history. 

The complex political, sociocultural, and environmental conditions in the Borderlands present challenges to understanding 

current conditions and planning for future sustainability, but the scientific expertise of the USGS can provide the data needed to

address those challenges. Communities and decisionmakers need sophisticated tools that accurately describe and monitor the 

state of the environment through the development and application of environmental indicators. Environmental indicators are 

statistics, measures, or parameters that track changes over time and summarize complex information about the environment 

into key measures (physical, chemical, biological, or socioeconomic) to holistically evaluate the condition of the environment. 

Indicators are developed by synthesizing and transforming extensive scientific and technical data into simply stated, meaningful

information, providing an integrated approach to addressing environmental problems. Consistent measurement of indicators 

allows conditions to be assessed and monitored over short and long time periods and events to be forecasted or predicted. For 

example, the EPA identified the number of days during a given year in which air quality exceeded particulate matter standards

as an indicator of air quality in the lower Rio Grande valley. Data collected by the USGS can contribute to the development 

of similar environmental indicators in the areas of water, geography, biology, and geology. The USGS can also provide stateof-the-art geospatial and remote sensing technology, as well as the powerful data management and information dissemination 

capabilities that are used in indicator assessment and monitoring activities. In addition to the scientific and technological

capabilities of the USGS, its existing datasets for the Borderlands and its long-standing professional associations with Mexican 

scientists make it ideally suited to the development of environmental indicators in the Borderlands.

References cited in this chapter are listed in chapter 12.
Challenge Theme 4.

People in the Borderlands

By Laura M. Norman, Rudy M. Shuster, and Jean W. Parcher

Introduction

The management of shared resources in the United States–Mexican 

border region requires cooperation from the people of both countries 

to assess and understand their relation to the environment. Society is 

dependent on the long-term healthy functioning of ecosystems and their 

ability to supply food and raw materials. Likewise, resources and services 

obtained from nature could be used efficiently within the society. A more 

equitable distribution of costs and benefits related to goods and services 

can lead to fewer tensions and a higher quality of life for all the people 

in the Borderlands. Urban development, background contamination 

from mineral ore deposits, irrigation, sewage effluent, and even global 

climate change all have the potential to alter the stability of the fragile 

systems in the Borderlands (Brady and others, 2001, 2002; Norman, 

2007, 2010; Gu and others, 2008; Norman, Gray, and others, 2008; 

Norman, Hirsch, and Ward, 2008; Norman, Callegary, and others, 

2010; Norman, Huth, and others, 2010; Norman, Levick, and others, 

2010; Norman, Tallent-Halsell, and others, 2010; Norman, Villarreal, and 

others 2012). Social efficiency means that because resources should be 

Chapter 6
Challenge Theme 4. People in the Borderlands 117

used where they are needed most, they should be distributed proportionally among human 

societies and individuals (Azar and others, 1996). Despite the critical role natural resources 

play in maintaining human and environmental health, current knowledge of the manner in which 

natural and human-caused forces interact to limit these resources—including their quality and 

quantity (such as through spatiotemporal changes in precipitation, evapotranspiration, pumping of 

groundwater, and release of contaminants)—is inadequate. The U.S. Geological Survey (USGS) 

is trying to understand the relation between changing landscapes, changing demographics, and 

a changing climate in the Borderlands while the environmental, economic, and societal issues 

continue to be intertwined between the two nations.

Downtown Yuma, Arizona

Providing scientific information to land management and public policy decisionmakers

is at the heart of the USGS science strategy. 

By understanding the status of U.S. natural resources, how natural resources interrelate 

and change with time, and how resilient they are to future natural and human-caused 

threats, decisionmakers will be able to ensure the security of the Nation, the vitality 

of its economy, the health of its environment, and the well-being of its citizens. 

(U.S. Geological Survey, 2007, p. 1, emphasis added)

Specifically, the USGS provides unbiased, multidisciplinary science in the context of climate/

global change, water, natural hazards, and human health risks so decisionmakers can assess 

the interrelations and effects of these issues on human populations. The climate research 

goals of the USGS are also outlined in the science strategy.

The USGS will conduct research to advance the knowledge of processes that are 

crucial to predicting the future evolution of global climate and to understand the land, 

water, environmental, and societal consequences of changing climate. *** Studies 

of the probability and consequences of abrupt changes and thresholds will be used 

to clarify the nature of change and the effects on the environment and society. 

(U.S. Geological Survey, 2007, p. 16, emphasis added)

Combining the results of USGS natural and biological science with socioeconomic research 

fosters resilience in human communities and throughout the socioecological system. 

The USGS science strategy uses the concept of complex and nonlinear relations to frame 

the interactions between social and ecological systems. For example, a wildlife preserve might 

be dependent upon a watershed that contains intense human development (cities, industrial 

centers, etc.). The human communities might be dependent on the ecological system within 

the wildlife preserve for ecosystem services such as drinking water purification or subsistence

hunting for local populations. Climate change might result in increased precipitation within the 

watershed, which would lead to increased runoff bringing industrial pollutants into the ecological 

system. Native vegetation might adapt to the increased pollutants, and the wildlife might adapt 

to a new habitat. This relation is complex but with an obvious cause and effect; anticipating 

and managing these relations and the resulting effects to humans, however, is difficult. Nonlinear

relations have disproportionate cause and effect relations and are inherently difficult to manage.

Complex and nonlinear physical, chemical, and biological interactions are becoming 

an increasingly important focus for climate change assessments and basic research. 

*** but there is little insight into when biological thresholds will be crossed, much 

less on the implications for species, ecosystems, and the services society expects 

from the environment. (U.S. Geological Survey, 2007, p. 14, emphasis added)
Children playing in a makeshift swimming pool at a colonia in Aqua Prieta, Sonora, Mexico, in 2004

120 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

The socioecological systems (SES) method describes the complex relations between 

humans and their environment. It hypothesizes that the well-being of the ecosystems and 

human communities are co-dependent and must be managed simultaneously; changes in one 

system might cause changes in the other. The SES approach acknowledges not only that humans 

and nature are both nested in the system, but also that humans react to nature and nature 

reacts to human actions as two complementary but distinct entities within the system (Berkes 

and Folke, 1998; Carpenter and Folke, 2006). 

Governance systems are a third external factor influencing the SES and must be

accounted for. 

Institutions not only regulate the way humans relate to nature and how resources 

are used, both individually and collectively, but are at the core of the organizations 

(for example, governmental agencies dealing with Natural Resource Management) 

and governance systems (including public and private spheres). (de la Torre-Castro, 

2009, p. 437). 

One example of governance driving science in SES is Executive Order 12898, “Federal Actions 

To Address Environmental Justice in Minority Populations and Low-Income Populations,” 

issued in 1994 (U.S. President, 1994). The order mandated that each U.S. Federal agency 

make environmental justice part of its mission by focusing on how agency policies and actions 

affect the relation between human health and environment in low socioeconomic and high 

minority communities. The U.S. Environmental Protection Agency (EPA) defines environmental

justice as 

...the fair treatment and meaningful involvement of all people regardless of race, 

color, national origin, or income with respect to the development, implementation, 

and enforcement of environmental laws, regulations, and policies. EPA has this goal 

for all communities and persons across this Nation. It will be achieved when everyone 

enjoys the same degree of protection from environmental and health hazards and 

equal access to the decision-making process to have a healthy environment in which 

to live, learn, and work. (U.S. Environmental Protection Agency, 2012a)

Cacti along a 

Central Arizona Project canal

Executive Order 12898
Challenge Theme 4. People in the Borderlands 121

Acknowledging the relations among the social and ecological systems is integral to successfully applying scientific

information in resource management and governance (Pachauri and others, 2007; Resilience Alliance, 2007 a, b). The social system 

is a strong driver of change in ecological systems—increased human development pressure has pushed the limits of adaptability 

in ecological systems—but adaptability in ecological systems drives and limits change in social systems. The complexities of the 

SES have created problems and questions that are not confined to a single scientific discipline. Interdisciplinary research among

social, behavioral, economic, and natural/biological scientists is necessary to solve these problems and develop new technologies to 

manage social and ecological systems within their limits of adaptability (National Academy of Sciences, 2005).

Human uses of natural resources, although required for civilization, might also lead to undesirable ecological consequences, 

which often create environmental justice issues in low socioeconomic and high minority communities at a disproportionately 

high rate in comparison to more affluent communities. According to Moda (2007), a large number of communities suffer from 

environmental justice issues in the United States portion of the Borderlands, where 25 percent or more of the population lacks 

native language proficiency, 25 percent or more of the population is foreign born, 25 percent or more of the population is minority,

and (or) median annual income of the population is at or below 65 percent of the State median income. The distribution of 

environmental hazards (for example, contaminated drinking water, decreasing water yields, or susceptibility to flooding) has

shown high frequency in low income, high minority communities along the border (Norman, Caldeira, and others, 2012). Rural 

communities along the border are also confronted with multiple environmental justice issues: illegal dumping of trash and (or) 

industrial waste, agricultural drainage, exposure to airborne dust and pesticides, inadequate water supplies, insufficient waste

facilities, and degraded natural resources and ecosystems (Norman, Hirsch, and Ward, 2008; Norman, 2010). In addition, the 

World Health Organization has identified that these communities are more vulnerable and susceptible to local health effects of

climate change (Patz and Balbus, 1996). 

The United States–Mexican border region is an area where the SES and governance structures interact to create a complex 

natural resource and policy decisionmaking arena. In the United States, mandates such as the environmental justice Executive 

Order drive the need for scientific environmental information in a specific social context. The USGS is dedicated to providing

scientific information to assist in this complex decisionmaking through projects that integrate social, behavioral, economic, and

natural science analyses in the context of human and natural resource interactions. The international border separating the two 

countries, however, further complicates matters because differences in culture, language, priority, law, and policy interrupt 

management of an environment that spans the border. Science that crosses the border needs to be coordinated in order to 

understand the human drivers of undesirable consequences and forecast socioecological events. The sections that follow in this 

chapter showcase USGS capabilities and projects, both completed and ongoing, and list areas where more science is needed.
maquiladora

122 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Population Growth

The populations on both sides of the border respond to ebbs and flows in social and economic change—largely dependent

on current regulation. Policy reforms on both sides of the border greatly affect how and where human populations migrate 

and reside. Labor shortages in the United States brought about by World War II instigated reliance on Mexican workers. In 

response, the Bracero Program, in effect from 1942 through 1964, encouraged millions of Mexicans to work in the United States 

(Donelson and Esparza, 2007). During the 1960s, Mexico started two important programs: El Programa Nacional Fronterizo 

[the National Border Program] and the Border Industrialization Program (BIP). The purpose of the BIP was to aid the economic 

development of northern Mexico by attracting foreign assembly firms, called maquiladoras, to the border region (Garibay, 1977).

Maquiladoras are factories that can be owned and operated by United States companies though they are located in Mexico. These 

factories import raw materials on a tax-free basis into Mexico for use in manufacturing and then export products back to United 

States markets. Maquiladoras often employ laborers from Mexico at what can be considered low wages compared to American 

standards. In addition, because they are located in Mexico, they do not necessarily have to conform to the strict building and 

processing codes required in the United States (Donelson and Esparza, 2007). The North American Free Trade Agreement 

(NAFTA) in 1994 was designed to foster greater trade between Canada, the United States, and Mexico through the elimination 

of taxes on goods shipped between these countries. The agreement created favorable economic conditions for the expansion of 

maquiladoras in border communities, thus creating incentives for individuals to migrate to the border cities. Low wages paid to 

Mexican workers and high productivity have attracted foreign investment and job creation at the border, which have contributed 

to the huge population expansion in arid areas that have diminishing and effectively irreplaceable water resources (Ingram and 

Varady, 1996; Norman, Donelson, and others, 2006).

Inside a maquiladora in Mexico
Mexican workers at Mexicali, Baja California, waiting for legal employment in the United States, 1954

Challenge Theme 4. People in the Borderlands 123

Mexican 

immigrant near 

the border, 1950

The demographic settlement pattern of the Borderlands follows the world trend toward 

increased urbanization (14 percent urban in 1900 rising to almost 50 percent urban in 1990), 

shifting the population from rural farms to integrated population centers (Douglas, 1994). 

Because of the binational heritage in the region, populations on both sides of the border are 

interconnected economically, politically, and socially, and 14 sister city pairs have developed 

as a result (Parcher, 2008). (Sister cities or twin cities are those communities where a city in 

one country borders a city in the other, creating a large urban area separated by political and 

administrative boundaries. For a list of sister cities in the Borderlands, see table 2–1.) Families 

and individuals from southern Mexico interested in improving their status migrate to these 

regions in search of employment. Migration is the primary factor for urban population growth 

at the border and is compounded by increasing birth rates. Population growth rates in both 

Mexican and United States sister cities are more than double the national averages (Peach 

and Williams, 2003), and if current trends continue, the resources available to these cities will 

quickly become overburdened. Rapid population growth in urban areas has led to increases in 

the demand for land and energy, traffic congestion, and the generation of wastes—all of which

affect available resources and contribute to environmental justice issues.

Prediction of urban growth can help promote understanding of potential effects of growth 

on water resources, the economy, and the people. Researchers with the USGS Geographic 

Analysis and Monitoring Program used the SLEUTH1

 urban growth model to study patterns of 

growth and identify potential areas of future populations in the sister cities of Nogales, Arizona, 

and Nogales, Sonora (Mexico) (Norman, Feller, and Guertin, 2009). Model results demonstrated 

that the sister cities are undergoing very different processes of change. Generally speaking, 

Nogales, Ariz., is a small city, adhering to urban-planning restrictions, and has a relatively 

low household income for the State of Arizona. In contrast, Nogales, Sonora, is quite large 

and is growing without much restriction to slope, natural hydrology, or infrastructure 

capacity because it offers so much employment opportunity for people south of the border. 

Within Nogales, Sonora, the 2000 census recorded a population of 159,787 with an annual 

growth rate of 4.9 percent. In 2009, unofficial estimates suggest the population is closer to

300,000. Based on urban growth scenarios predicted by Norman, Feller, and Guertin (2009), the 

SLEUTH model predicted that by 2030 the Nogales, Sonora, urban area would grow to almost 

3.5 times its size in 2002. Temporal urban mapping and growth predictions such as described 

here can be analyzed for patterns, rates, and trends in land use and can assist decisionmakers 

in evaluating the relative merits of the various land use and urban development options.

1

 SLEUTH—slope, land cover, exclusion, urbanization, transportation, and hillshade.

Laborers return to Mexico after 

working in the United States, 

1954

Mexican laborers working in 

southern California as part of the 

Bracero Program, 1963
124 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

then

View of the Franklin Mountains 

and El Paso, Texas, in 1909

View south into Ciudad Juarez, 

Chihuahua, from El Paso, Texas. 

The line of yellow light is the 

international border.
Challenge Theme 4. People in the Borderlands 125

now

View of the Franklin Mountains 

and El Paso, Texas, in 2012
126 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Land Use

The study of land-use and land-cover (LULC) change is a science that describes human 

modification of the Earth’s surface. Humans modify land to obtain food, energy, and natural

resources and to pursue outdoor recreation, and these modifications cause changes in ecosystems

and environmental processes at local, regional, and global scales. These changes encompass 

the greatest environmental concerns of human populations today, including climate change, 

biodiversity loss, resource management and planning, resource security, disaster planning, and 

the pollution of water, soils, and air.

Land use normally refers to human activities upon the landscape. Geographers monitor 

changes to the landscape by using standardized land-use categories. The term land cover refers 

to the character of the landscape surface—vegetative cover, water, or other earth materials. 

While land-use changes normally result from a shift in human activity, land-cover changes 

result from physical changes to the environment, which can be natural or human-induced. 

The process of urbanization has a considerable effect and influence on environmental

characteristics (Norman, Guertin, and Feller, 2008; Norman, 2010; Norman, Feller, and 

Villarreal, in press). The Land Cover Trends research project at the USGS focuses on 

understanding the rates, trends, causes, and consequences of contemporary U.S. land-use 

and land-cover change, including urbanization. The results from this research provide a 

foundation for modeling future landscape changes and predicting the effects of these changes.

El Paso, Texas

Padre Island 

National Seashore, Texas
Challenge Theme 4. People in the Borderlands 127

Colonias

In Spanish, the word colonia translates to neighborhood; in the United States, however, the word has taken on a whole new 

meaning. As a result of the 1990 Cranston-Gonzalez National Affordable Housing Act, colonias were defined as rural, mostly

unincorporated communities in California, Arizona, New Mexico, and Texas within 150 miles of the United States–Mexican 

border that lack adequate infrastructure or housing, as well as other basic services. The colonias typically are located outside of 

an established municipal jurisdiction and have high poverty rates, making it difficult for residents to pay for roads, water sanitation

and sewer systems, minimum-standard housing, street lighting, and other services; in Mexico, these communities are referred 

to as colonias marginales (poor neighborhoods; Norman, Donelson, and others, 2004; Norman, Parcher, and Lam, 2004; Lam 

and others, 2006; Norman, Donelson, and others, 2006; and Norman, 2010).

Colonias and colonias marginales are scattered along both sides of the border as makeshift settlements, commonly on private 

land. Because these settlements have been established outside the formally sanctioned governance of nearby cities and towns, 

colonia residents have traditionally struggled to gain access 

to the public services available in those communities. Most 

of the border communities in the United States have failed to 

acquire federally allocated dollars to improve their environment 

because they lack the capacity to do so. Only a very small 

number of colonias have relationships with funding 

institutions, and many lack community-based organizations 

that can access and use resources available to improve the 

local quality of life (Ward, 1999).

Houses near the United 

States–Mexican border in 

Sonora (top) and Sunland Park, 

New Mexico (left)
The United States and Mexico both have programs to produce land use 

and land cover (LULC) datasets using a nationally consistent classification 

scheme. The USGS National Land Cover Dataset 1992 (NLCD 1992; Vogelmann 

and others, 2001) and the National Land Cover Database 2001 (NLCD 2001; 

Homer and others, 2004) are based on the LULC classification system for 

remotely sensed data described by Anderson and others (1976). In Mexico, 

the Instituto Nacional de Estadística y Geografía (INEGI) [National Institute of 

Statistics and Geography] is responsible for mapping LULC. The INEGI produces 

the 1:250,000-scale Mapa de Uso de Suelo y Vegetación [Land Use and 

Vegetation Map] based on visual interpretation of remotely sensed imagery 

using unified regional vegetation classification systems developed over the 

last 70 years by many scientists (Instituto Nacional de Estadística, Geografía 

e Informática, 1993). An integral part of the USGS Border Environmental 

Health Initiative (BEHI) United States–Mexico geospatial database is an LULC 

dataset integrating information from both countries. Integration of the United 

States and Mexican data required the creation of a generalized (modified 

Anderson Level I) binational classification system to which both countries’ 

LULC data could be reclassified (Anderson and others, 1976). 

The 1992 and 2001 binational LULC datasets are being compared to 

formulate a synthesis of land-use change for major watersheds along the 

United States–Mexican border, and the results are being analyzed in 

combination with anthropogenic drivers in the border region. Trends can 

be used to predict future landscape changes, to monitor changes to water 

demands, and to statistically analyze landscape fragmentation.

Binational Land Use and 

Land Cover Database

. . . .facing the challenge
0 10 20 30 40 KILOMETERS

0 10 20 30 40 MILES EXPLANATION

Subarea of the border region

8 Lower Rio Grande Valley

International boundary

8

Land use/land cover

Developed

Agriculture

Forest

Shrubland

Water

Barren

Grassland/pasture

Wetlands

TEXAS

NUEVO

LEÓN

NUEVO

LEÓN

TAMAULIPAS

UNITED STATES 

MEXICO

Gulf of Mexico

8 RIO GRANDE

RIO BRAVO Brownsville

McAllen

Reynosa

Matamoros

100°00’ 99°30’ 99°00’ 98°30’ 98°00’ 97°30’

25°30’

26°00’

26°30’

27°00’

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

8

Challenge Theme 4. People in the Borderlands 129

Binational land use and land cover classifications in the Lower Rio Grande Valley subarea 

(Texas, United States, and Nuevo León and Tamaulipas, Mexico). Derived from the U.S. 

Geological Survey 1992 National Land Cover Dataset and data from the Border Environmental 

Health Initiative in the United States and the Instituto Nacional de Estadística y Geografía 

[National Institute of Statistics and Geography] Uso de Suelos y Vegetación [Land Use and 

Vegetation] dataset in Mexico.
Buildings in Lomas de Poleo, a colonia outside of Ciudad Juárez, Chihuahua

CALIFORNIA

130 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

The USGS and the U.S. Department of Housing and Urban Development, in cooperation 

with the Mexican Instituto Nacional de Estadística y Geografía (INEGI) [National Institute of 

Statistics and Geography], developed a joint project to create Internet-enabled geographic 

information systems (GIS) to help cities along the United States–Mexican border manage 

issues related to urban growth and low-income housing developments. This joint project 

delineated colonias in Arizona and Sonora and developed publically available Internet map 

services of geospatial databases describing infrastructure and land use for the entire border. 

In Mexico, colonias marginales were also identified in this scope of work (fig. 6–1) (Norman,

Donelson, and others, 2004; Norman, Parcher, and Lam, 2004; Norman, Donelson, and 

others, 2006). Data were integrated from various Federal agencies in both the United States 

and Mexico. This project was the precursor for the United States–Mexico Border Geographic 

Information System (USMX-GIS). The colonias designation by Federal agencies is important 

because it gives recognition to neighborhoods suffering from environmental justice issues 

and government recognition makes them eligible for associated funding.2

2

 For more information, see Executive Order 12898 (U.S. President, 1994), the U.S. Environmental Protection Agency–

Office of Environmental Justice page for information on grants and programs (http://www.epa.gov/environmentaljustice/

grants/index.html), and the U.S. Department of Housing and Urban Development page on funding for colonias and 

farmworkers (http://www.hud.gov/groups/funding.cfm). 
TEXAS

NEW MEXICO

UNITED STATES

MEXICO

ARIZONA

NEW MEXICO

CHIHUAHUA

COAHUILA

BAJA

CALIFORNIA

SONORA Gulf of California

PACIFIC OCEAN

Douglas

Agua Prieta

colonias

Challenge Theme 4. People in the Borderlands 131

Figure 6–1. Examples of 

colonia residences along 

the United States–Mexican 

border in a colonia at 

Douglas, Arizona, United 

States (top) and across the 

border in a colonia marginal 

at Agua Prieta, Sonora, 

Mexico (bottom), 2004.
With the passing of Senate bill 827 (SB 827) by the 79th Texas Legislature 

in 2005, the State was mandated to create a colonia identification system 

and track the progress of State-funded colonia improvement projects. These 

efforts were spearheaded by the Office of the Secretary of State (SOS) of 

Texas, and as a result the SB 827 workgroup was formed (Office of the Texas 

Secretary of State, 2006). In order to track the progress of State-funded 

projects, the SB 827 workgroup created a set of infrastructure, demographic, 

and health-related criteria for ombudsmen in the field to collect. The ombudsmen 

collected data through site visits and from a variety of sources, including 

utility companies, county appraisal districts, and the Office of the Attorney 

General of Texas.

Because colonias are not uniquely identified within the census geography 

but instead are sometimes nested within or astride census blocks, an explicit 

long-term working database is needed to monitor progress, set infrastructure 

priorities, and measure quality of life indicators within the colonias. Based 

on requirements outlined in SB 827, and in cooperation with the Texas SOS, 

the USGS developed the Colonia Health, Infrastructure, and Platting Status tool 

(CHIPS). The CHIPS tool is a relational database that uses the classification 

criteria created by the SB 827 workgroup as a template for the database 

schema (Parcher and Humberson, 2007). Once these data were collected, 

each colonia was classified into categories, according to whether or not the 

colonia (1) had already been platted, (2) had a potable water supply, (3) had 

adequate wastewater disposal, (4) had adequate trash collection, and (5) had 

paved roads with adequate drainage. With the CHIPS report generator and 

the accompanying maps, local governments are now able to set priorities for 

colonia projects.

CHIPS—A New Way To Monitor 

Colonia Development along the 

United States–Mexican Border

. . . .facing the challenge
Challenge Theme 4. People in the Borderlands 133

Database schema for the Colonia Health, 

Infrastructure, and Platting Status tool. 

From Parcher and Humberson (2007).
Sustainable Development

Maintaining sustainable development of this region can be facilitated by actively studying 

and monitoring the nexus of science, society, and resource management to determine the 

minimum effects that growth will have on the environment. Because the administration of 

the Borderlands is divided between two countries, identifying the consequences of change 

throughout the whole border region is difficult. As such, it is essential to regional planning

efforts to understand the ramifications of human activities on both sides of the border and to

provide information to decisionmakers in both countries simultaneously. Binational sustainable 

development includes land-use planning and management that integrates and coordinates 

environmental infrastructure for water, sanitation, drainage, and solid waste management; 

develops sustainable energy and transportation systems; combines binational disaster response 

strategies; and regulates industry. The economy and natural resource availability are major 

factors in decisions regarding urban development, settlements, agricultural practices, and the 

disturbance of historical natural and cultural resources. Socioeconomic concerns, including 

equity, are among the primary recognized components of sustainability; social factors have 

been described as one leg of the three-legged sustainability “stool,” with the other legs being 

the environment and the economy (Morrison-Saunders and Therivel, 2006). 
Challenge Theme 4. People in the Borderlands 135

The USGS programs can identify people and communities that might be unduly affected 

by development plans. Norman, Villarreal, and others (2012) have developed and applied the 

Modified Socio-Environmental Vulnerability Index (M-SEVI) using binational census data to

map vulnerable populations; this index provides a base reference to compare to models of 

biophysical conditions, including land-use or climate change, and examine if changes in 

hydrology, surface conditions, biodiversity, and (or) property values could affect low income 

or high minority communities unfairly, creating issues of environmental justice. The USGS 

can assist with sustainable-development planning in both countries by providing integrated 

binational databases, maps, and predictive models such as the index described above to find

scenarios that reduce hazards and other effects of urbanization. 
The Nogales-Nogales sister city area (Arizona-Sonora) is located in the 

Ambos Nogales watershed, a topographically irregular bowl-shaped area 

with a northward gradient. Throughout recent history, residents in both cities 

have been affected by flooding. Extreme flood events cause surface materials 

to erode, and eroded materials put pressure on over-burdened water and 

wastewater infrastructure in the Ambos Nogales watershed. The encroachment 

of population and transportation routes on the floodplains and drainages 

of the Nogales Wash and its tributaries poses future risks on exacerbated 

systems. The resulting constriction of stream channels has concentrated 

flow during periods of heavy monsoonal precipitation, common during summers 

in this area. These flows erode loose alluvial sediments and disturbed soils 

along the banks of washes. The primary means of regulating this runoff is a 

series of detention features in Nogales, Sonora. Land managers on both sides 

of the border seek information to increase detention feature effectiveness by 

optimizing future locations. Flood peaks and erosion associated with seasonal 

monsoonal rains must be reduced in order to enhance public safety and health.

Researchers with the USGS are using geospatial models to project 

the effects of possible influences such as predicted urban development, 

small detention reservoirs, and potential climate change on flood hydrographs and sediment yield. Using the results of coupled urban growth, erosion, sedimentation, and runoff models in a virtual environment, the USGS can 

also make estimates of current and future hypothetical water resource conditions to identify nonpoint source pollution. For the Ambos Nogales watershed, 

researchers with the USGS Geographic Analysis and Monitoring Program 

assessed the effects of land-use change by using hydrologic models to predict 

runoff volumes and peaks in order to identify best management practices 

to offset monsoonal flooding. They applied the SLEUTH urban growth model 

to the Nogales-Nogales sister city area to identify potential areas of future 

populations (Norman, Feller, and Guertin, 2009). Growth predictions were 

coupled with results from erosion-sedimentation models to simulate the effect 

of excluding hot-spot areas of nonpoint source pollution. Alternative future 

scenarios were then published that identify sustainable development zones 

in which Borderland populations can grow (Norman, 2007; Norman, Guertin, 

and Feller, 2008; Norman, Feller, and Guertin, 2009). The KINEROS21

 model 

was used to evaluate the Ambos Nogales watershed vulnerability to flooding 

1

 KINEROS—kinetic runoff and erosion.

Binational Planning at 

Ambos Nogales

. . . .facing the challenge
Nogales,

ARIZONA

Nogales,

SONORA

UNITED STATES

MEXICO

Challenge Theme 4. People in the Borderlands 137

Flooding on the Nogales Wash in Nogales, Arizona, damaged 

the waterway, as shown here near the Chula Vista Flood Control 

Project site in July 2010. The Ambos Nogales watershed (inset) 

includes the Nogales-Nogales sister city area; the international 

border runs diagonally through the photo with Arizona on the 

lower left and Sonora on the upper right. 

(Norman, Huth, and others, 2010). The International Boundary and Water Commission funded a higherresolution study to determine the effects of detention features in Nogales, Sonora, and estimate the 

volume of water being detained and the magnitude of discharge under various urbanization scenarios 

and return periods of 10, 25, and 100 years (Norman, Levick, and others, 2010). This project is considered 

the first step of a locally driven strategy for a binational sustainable development. By integrating current 

and accurate information into the general municipal plan and partial urban plans, the sister city area 

can implement measures that will diminish adverse effects of runoff and flooding in the downtown area, 

reduce nonpoint source pollution and sediment loading in surface water, and decrease human exposure 

to chemicals, pathogens, and disease vectors (Norman, Hirsch, and Ward, 2008; Norman, Huth, and others, 

2010; Norman, Levick, and others, 2010).
138 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Ecosystem Services

Ecosystem services are the goods and benefits that people obtain from ecosystems (DeGroot and others, 2009), such as

clean drinking water or firewood. Use of this term to describe the relation of people to their ecosystems has been growing since

the 1960s, and the concept has been gaining momentum as a framework in which to integrate ecological function and economics 

in a manner useful for evaluating tradeoffs in natural resource management (Wainger and others, 2009). The ecosystem services 

framework allows one to balance competing interests when deciding how best to manage and allocate natural resources (Fisher 

and others, 2009). It is critical for neighboring towns, counties, and even countries to monitor the forces changing their shared 

environment, and also to examine, document, and model potential implications for inhabitants. Given the potential importance 

of transboundary ecosystem services, mechanisms for monitoring the indirect and direct drivers that affect the provisioning of 

ecosystem services and human welfare across the United States–Mexican border are needed (López-Hoffman and others, 2010; 

Norman, Tallent-Halsell, and others, 2010; Norman, Villarreal, and others, 2012).
Challenge Theme 4. People in the Borderlands 139

Quality of life can be defined as the degree of well-being felt by an individual or group

of people. Although quality of life cannot be measured directly, it can be described in terms 

of physical and psychological values (Wainger and Price, 2004). There is a great disparity of 

economic resources in the Borderlands that affects infrastructure development and other quality 

of life issues. The northern region of Mexico is more affluent than the rest of the country, but

the border counties in the United States are among the poorest in the country (U.S. Environmental 

Protection Agency, 2012b). The ability to assess risks and implement policies to protect the 

environment and quality of life greatly increases in complexity along international borders, 

where the social services, environmental regulations, lifestyles, and cultural beliefs of the 

neighboring countries are distinct (Parcher and others, 2006). Healthy natural systems have a 

profound effect on our quality of life by purifying air and water, stabilizing climate and soils, 

and providing raw resources. The natural resources surrounding resource-proximate human 

communities often contribute to the community identity and sense of place creating a location 

where people want to reside. Understanding the transactional relation between natural resource 

quality and human quality of life in resource-proximate communities is an important facet 

of making land management decisions. The benefits supplied to human societies by natural

ecosystems are sometimes overlooked until after decisions are made and negative effects of 

those decisions spur public reaction. The USGS can use an ecosystem services approach to 

promote good decisionmaking by determining how much ecosystems contribute to a society’s 

well-being and providing an understanding of the services and valuation (nonmonetary and 

monetary) of an ecosystem.

San Diego harbor
140 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
Challenge Theme 4. People in the Borderlands 141

A region’s ecosystem and its people are inextricably linked. The 

well-being of the human community relies on and influences the 

well-being of the ecosystem, and the natural landscape and its 

resources contribute to the identity of the community living within it.
A consortium of Federal, academic, and private partners have established 

a collaborative research enterprise in the San Pedro River basin to develop 

methods, standards, and tools designed to map, assess, and value ecosystem 

services (Semmens and others, 2008). The central premise of ecosystem 

services research is that the human condition is inseparably linked to the 

environment and that human health and well-being (including economic 

prosperity) depends on the important supportive functions and cultural services 

provided by our surrounding ecosystems, as well as on the regulation and 

provisioning of those systems. The AGAVES project—Assessment of Goods 

and Valuation of Ecosystem Services—is intended to demonstrate that scientists 

and stakeholders can work together to facilitate environmental management 

and planning by incorporating information on the goods and services derived 

from the San Pedro River basin.

The San Pedro River is one of the last free-flowing, perennial rivers in the 

southwestern United States, originating in Sonora, Mexico, and flowing north 

into southeastern Arizona (Thomas and Pool, 2006). The river hosts a rich 

riparian community with vital habitat for diverse populations of resident and 

migrant species. Decades of groundwater overdraft and a recent drought 

have significantly reduced base flows in the San Pedro River, and rapid 

urbanization and anticipated climate change both exacerbate this problem.

A AVES—Assessment of 

oods and Valuation of 

Ecosystem Services in the 

San Pedro River Basin, 

United States and Mexico

G

G

. . . .facing the challenge
Challenge Theme 4. People in the Borderlands 143

The San Pedro River 

The unique combination of existing data, previous research, established partnerships, and humaninduced environmental stressors on and surrounding the San Pedro River represents the ideal conditions 

in which to apply the ecosystem services conceptual framework and evaluate its efficacy for resource 

management and planning. The AGAVES project has partnered with key stakeholders and managers in 

the San Pedro River basin to ensure that it will address both the ecosystem goods and services of greatest 

concern to local residents (water, biodiversity, recreation, and carbon sequestration) and the management 

alternatives that are most widely accepted by the communities in the basin (controlling invasive mesquite 

and water augmentation). The effectiveness of these management alternatives in preserving the key 

services will be explored under a range of potential future conditions as defined by the degree of urban 

growth and climate change in the basin. The ultimate goal of the AGAVES project is to develop the methods 

and tools that will help resource managers understand the tradeoffs associated with management 

alternatives and make difficult decisions about how to best preserve the ecological and economic 

prosperity currently enjoyed in the San Pedro River basin.
Farm on the Tohono O’odham reservation

144 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Native American Resources

In the Borderlands, there are 26 Native American tribes recognized by the United States 

Federal Government and 7 Indigenous tribes recognized by the Mexican Federal Government, 

with populations ranging from 9 to 17,000 members. Indigenous nations divided by the United 

States–Mexican border include the Kumeyaay of California/Baja California; the Tohono 

O’odham, Pascua Yaqui, Gila River Indian Community (Akimel O’odham), Cocopah, and 

Yavapai-Apache of Arizona/Sonora; and the Kickapoo of Oklahoma, Kansas, and Texas/

Chihuahua. Adjacent to the Native American nations in the United States are lands administered 

by various bureaus in the U.S. Department of the Interior, U.S. Department of Commerce, and 

U.S. Department of Defense. 

Tribal lands are of cultural importance because they contain sites with cultural artifacts 

and often are the ancestral homelands of the Native Americans. In the United States, the 

Bureau of Indian Affairs, the Federal Bureau of Investigation, the U.S. Border Patrol, the 

National Park Service, and law enforcement officials of the Native American nations have

documented that Native American cultural sites and resources are being lost to vandalism and 

trafficking of artifacts. Ensuring surveillance and law enforcement of areas with at-risk heritage

sites is difficult or impossible, due in part to the remoteness of many of these sites. Further

complicating the issues, the identification of sites of cultural importance is not documented in a

holistic manner because of the patchwork pattern of land administration, 

which makes coordinated regional management by Federal, State, 

and Native American agencies difficult. Because vandalism

and trafficking encompass both destruction of sites and

transport of cultural materials, the loss to our understanding 

of the historic and prehistoric human occupancy of the 

Borderlands is extensive and irreversible. 
Challenge Theme 4. People in the Borderlands 145

The USGS has a firm commitment to work collaboratively with Native American nations across the United States in areas

of education, natural resources, and the development of sustainable capabilities (Marcus, 2010). In the Borderlands of Arizona 

and Sonora, the USGS, in collaboration with the EPA and the Bureau of Reclamation, is working with the San Xavier District of 

the Tohono O’odham Nation to develop a pilot tribal study to understand the effect that water and land management will have 

on the goods and services derived from natural and cultivated ecosystems. The goal of this tribal pilot study is to investigate the 

feasibility of using an ecosystem services approach to assess the ecological, economic, and social ramifications of alternative water

allocation in regards to the historic ties tribal populations have to the land, their dietary practices, and the recreation value and 

spiritual and cultural resources of the land (Hall and others, 2010; Tallent-Halsell and others, 2010). Assistance in the preservation 

of cultural resources can be a cornerstone of USGS and Native American collaboration. Remote sensing, geospatial derivative 

maps of special areas, corridor map products, relational databases, and ground-based land surveys supported by global positioning 

systems (GPS) can assist Federal and Native American planners, enforcement officials, and decisionmakers.

Tohono O’odham basketmaker, 

Arizona, 1916

Hohokam petroglyph, Signal Hill, 

Saguaro National Park, Arizona
146 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Border Environmental Health Research

Consistent with environmental justice mandates, border environmental health efforts focus on reducing risks to border 

families, especially children, of exposure to air pollution, drinking water contaminants, pesticides, and other toxic chemicals 

(Parcher and others, 2006). The USGS Border Environmental Health Initiative project (BEHI; http://borderhealth.cr.usgs.gov) 

is committed to two goals: (1) to develop and maintain the USMX-GIS and natural resource databases to assist in decisionmaking 

concerning the United States–Mexican border region; and (2) to investigate the connections between the condition of the physical 

environment and environmental and health issues along the border.

The primary objective of the BEHI project is to provide binational science data in support of environmental health studies that 

will enable scientists, public health officials, resource managers, and concerned citizens to make informed decisions. Geographers,

biologists, hydrologists, and geologists with the USGS have accomplished this goal by implementing a comprehensive binational 

environmental resource database within a GIS framework. The USMX-GIS developed by the BEHI project is available as 

both an Internet map service (http://txpub.usgs.gov/borderhealth/) and as a download from a file transfer protocol (FTP) Web

site (http://borderhealth.cr.usgs.gov/datalayers.html). The databases and Internet map service provide a framework in which 

researchers can examine both the occurrence and distribution of disease-causing agents in the environment and their specific

exposure pathways in water, air, biota, rock, and soil. A desired outcome of this project will be the identification of information

gaps and enhanced opportunities for collaborative research with public health agencies and biomedical researchers. 
Escherichia coli, commonly 

abbreviated E. coli

Challenge Theme 4. People in the Borderlands 147

The second objective of this initiative is to examine and analyze 

connections between human and environmental health through 

collaborative opportunities with natural resource scientists, 

managers, and public health officials. The USGS is actively seeking

to develop partnerships along the United States–Mexican border 

to further develop spatial products and use existing spatial 

data to understand the sources, distribution, and exposure 

pathways of environmental stressors and diseases. Some of 

the intended outcomes of these research efforts are to 

characterize unhealthy environments, to provide information 

on how degraded environments affect the health of humans 

and wildlife at the landscape and population levels, and to 

better understand the nexus among environment, wildlife, 

and human activities as those interactions contribute to 

overall environmental health.

The focus of current USGS BEHI research is to 

understand and document the complex movement of natural 

and human contaminants through the upper Santa Cruz River 

watershed in Arizona and Sonora. Because of the diversity in the 

natural ecosystem, an interdisciplinary team of USGS scientists has 

been formed to identify risks to water resources in the Santa Cruz 

watershed, specifically (1) natural surface-water and groundwater flow;

(2) anthropogenic water flow (flood diversion, sewage effluent, wells, irrigation,

etc.); (3) human population growth and urbanization; (4) sources and distribution of mineral 

contaminants; (5) sources and distribution of disease; and (6) the health of local flora and fauna

(Callegary and others, 2010; Norman, Callegary, and others, 2010). Water samples, as well as 

samples of sediment, aquatic macroinvertebrates, aquatic plants (macrophytes), algae, riparian 

grasses, fish, and birds, are being analyzed, and existing surface-water and groundwater models

are being used to assess contaminant and sediment transport. Researchers with the USGS are 

also working with public health officials to make the connection between water quality and its

effect on human health in colonias of Nogales, Sonora. Water samples were collected during 

both wet and dry climates (summer and winter of 2010) and analyzed for arsenic, mercury, 

lead, and bacteria such as Escherichia coli (Caldeira and others, 2010). The results of this data 

collection are being compared to a survey that was initiated to investigate health factors 

associated with sustainable water delivery in colonias in the Borderlands by asking for a 

description of a household’s water source, delivery, personal disinfection practices, and 

gastrointestinal disease frequency (Caldeira and others, 2011; Norman, Caldeira, and others, 

2012). The proposer is actively seeking collaborators in Nogales, Sonora, and invites feedback 

on the research plan and discussion with potential collaborators.

Decision Support Systems

In accordance with the USGS science strategy (U.S. Geological Survey, 2007), scientists 

can develop methods that can be used to minimize the negative effects of climate change and 

at the same time, by refining, applying, and interpreting watershed and ecosystem-process

models, can increase the understanding of forces that influence the structure and functioning of

ecosystems and the goods and services they provide. The USGS can support more comprehensive 

management strategies by providing resource managers with predictive modeling and decisionsupport capabilities that can forecast the effects of policy and management decisions concerning 

land, water, biological, and ecosystem resources using climate scenarios and data on natural 

and engineered changes in land use and land cover.
At the beginning of fiscal year 2010, the EPA Ecosystem Services 

Research program joined forces with the USGS Border Environmental Health 

Initiative (BEHI) and the Geographic Analysis and Monitoring Program to 

develop the Santa Cruz Watershed Ecosystem Portfolio Model (SCWEPM), an 

online decision-support tool based on ecosystem services (Norman, TallentHalsell, and others, 2010). Administration and ownership of the Santa Cruz 

watershed is divided between four governing nations: the Tohono O’odham 

Nation, the Pascua Yaqui Tribe, Mexico, and the United States. These large 

and diverse stakeholder groups share interests in farming, ranching, mining, 

economic and population growth, industry, and trade, as well as essential 

ecosystem services supported by the environment. Their management of 

land use affects natural processes and shapes the lay of the land. The broad 

objective of this study is to develop a reliable and useful online model-based 

scenario evaluation framework for the binational Santa Cruz watershed that 

can visualize and give structure to various scenarios of the regional effects 

on ecosystem services of future land-use change, climate change, and potential 

changes to engineered discharge from wastewater treatment plants. 

The Sonoran Desert, which overlaps part of the Santa Cruz watershed, 

is one of the largest, hottest, and most diverse deserts in North America. 

The dry climate is ideal for the many animals and plants that have developed 

adaptations to the biseasonal rainfall patterns and high temperatures, and 

the area also attracts humans who enjoy 

the warm climate, a low cost of living, an 

outdoor lifestyle, and scenic landscapes. 

However, deserts are extremely fragile 

and take a long time to recover from 

disturbance. The Sonoran Desert and 

the Santa Cruz watershed are within 

one of the most severely affected areas 

of the United States—the Borderlands, 

from southern California to west Texas—

according to modeled climate change 

predictions; potential effects are even 

greater over northern Mexico (Seager 

and others, 2007; Kerr 2008).

SCWEPM—

The Santa Cruz Watershed 

Ecosystem Portfolio Model

. . . .facing the challenge
Challenge Theme 4. People in the Borderlands 149

The Ecosystem Portfolio Model that was applied to the Santa Cruz watershed portrays the “pillars” 

of sustainability as three submodels that can be analyzed under various scenarios: the ecological-value 

submodel, the human well-being submodel, and the market land-price submodel (Labiosa and others, 

2009). The SLEUTH urban growth model also was applied to the Santa Cruz watershed to envision and 

evaluate plausible future scenarios and potential effects on ecosystem services for the year 2050. The 

SCWEPM was calibrated with historical data extracted from a time series of satellite images developed 

for this purpose (Villarreal and others, 2011). Three specific scenarios within the SCWEPM are designed 

to simulate changing spatial patterns of land use under different conditions: (1) a current trends scenario, 

an analysis of unmanaged exponential growth; (2) a conservation scenario, with managed growth to 

protect the environment; and (3) a megalopolis scenario, in which growth is accentuated around a 

defined international trade corridor. The alternative futures explore different patterns of impervious 

surfaces, different levels and patterns of habitat protection and land use, and different economic 

incentives to help guide planning for the future (Norman, Feller, and Villarreal, in press). 

Screenshot of the Santa Cruz Watershed Ecosystem Portfolio Model (SCWEPM) Web interface at http://lcat.usgs.gov/santacruz, 

developed by Dave Strong.

(Continued on page 150)
The ecological-value submodel was the first of three components to be 

included in the SCWEPM. We are calibrating the Soil and Water Assessment 

Tool (SWAT) at seven monitoring stations to improve model performance and 

reliability in this arid land (Niraula and others, 2012). With further calibration 

of the model for water quality parameters, the results of this research will 

be used to examine the flow and transport of contaminants and evaluate 

the effects of potential land-use and climate change on ecosystem services. 

Richness of terrestrial vertebrate species was mapped using wildlife habitat 

relation models and a high-resolution binational vegetation map (see Wallace 

and others, 2011), and the results were validated with data from local National 

Park Service biological inventories. The total number of potential terrestrial 

vertebrates was 451, only two less than the neighboring San Pedro watershed 

that is well-known for its conservation strategies. When the effects of urban 

growth on biodiversity were assessed, the current trends scenario showed a 

reduction and fragmentation of mammal and herpetofauna habitat, while the 

megalopolis scenario 

showed a likely loss of 

bird-rich riparian habitat 

caused by increased 

groundwater use (M.L. 

Villarreal and others, 

U.S. Geological Survey, 

written commun., 2012).

Greater Roadrunner

(Geococcyx californianus)

. . . .facing the challenge
Challenge Theme 4. People in the Borderlands 151

The human well-being submodel uses data and models to evaluate a set of human well-being indicators 

and metrics of interest to the public, land-use planners, and stakeholders. Using determinants from 

binational census and neighborhood data that describe levels of education, access to resources, migratory 

status, housing, and number of dependents, we developed the Modified Socio-Environmental Vulnerability 

Index to provide a simplified snapshot of the region’s populace that can be used in binational planning 

efforts (Norman, Villarreal, and others, 2012).

The market land-price submodel evaluates the price of land as a function of LULC patterns and other 

predictor variables. The market land-price submodel is based on hedonic-pricing functions, which describe 

each land parcel’s price in terms of its particular characteristics (for example, parcel size and zoning), 

as well as amenities and disamenities related to location. A hedonic analysis of residential property values 

is being developed that uses census block group data and geo-referenced environmental explanatory 

variables and accounts for spatial autocorrelation, lags, and (or) heterogeneity in the data (Arora and 

others, 2012). 

The SCWEPM Web interface allows the user to explore individual value maps for each unique criterion, 

or the user can select and apply multicriteria weights to view an aggregated value map and holistically 

compare potential land-use patterns. The user can also assign weights to each criterion or subcriterion 

to adjust the relative importance among the different criteria. Spatially-explicit criteria will be developed 

using the described models and data sources, and multi-attribute utility functions will be created based 

on stakeholder and public value. Public surveys in neighborhoods and colonias in the Santa Cruz watershed 

have been initiated to determine potential indicators (Weber and others, 2010). More modeling also needs 

to be done; climate change projections by the Intergovernmental Panel on Climate Change (see Solomon 

and others, 2007) will be used to simulate the effects of climate change on the watershed. 
152 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

 USGS Capabilities

Much is yet to be learned about the relation among changing landscapes, changing 

demographics, and a changing climate, which are superimposed in the Borderlands on an already 

complex mix of environmental, economic, and societal issues due to the differences in cultural 

and political mores of the two nations. Changes in the environment, the economy, and society 

are occurring rapidly in the Borderlands relative to other regions of the continent, and the USGS, 

with key partners, is in a unique position to address these changes and provide the scientific support

for policy decisions of both the United States and Mexico that could substantially enhance the 

quality of life in the Borderlands for decades to come. These concluding paragraphs offer examples 

of how the USGS is applying scientific methods to address the issues important to people in the

Borderlands, synthesizing the capabilities highlighted and referenced throughout this chapter.

The USGS is a leader in integration of United States and Mexican scientific data, as

demonstrated by the Border Environmental Health Initiative (Parcher, 2008). Specifically,

the USGS has examined and analyzed connections between human and environmental health 

through collaborative opportunities with natural resource scientists, managers, and public 

health officials (Norman, Hirsch, and Ward, 2008; Norman, Callegary, and others, 2010).

The USGS has also assisted with sustainable development planning by providing integrated 

binational databases, maps, and predictive models. These temporal urban mapping and growth 

predictions can be analyzed for patterns, rates, and trends in land use, as demonstrated by the 

alternative scenarios in the United States–Mexican Borderlands project (Norman, 2007, 2010; 

Norman, Guertin, and Feller, 2008; Norman, Callegary, and others, 2010; Norman, Huth, and 

others, 2010; Norman, Levick, and others, 2010). 

The USGS can estimate population change and migration in the Borderlands in light of 

land-use changes and for decisionmaking scenarios (Norman, Feller, and Villarreal, in press). 

We also have the capability to identify and map market and nonmarket ecosystem services 

(Labiosa and others, 2009) while providing economic impact analyses associated with binational 

land management decisions and natural resource changes (Semmens and others, 2008; Norman, 

Tallent-Halsell, and others, 2010).

The USGS capabilities also include collecting scientific data to understand the transactional

relation between natural resource quality and human quality of life in resource-proximate 

communities. This information can be reported in a context to facilitate land management 

decisions that take into account the socioecological system (Norman, Villarreal, and others, 

2012). Scientists with the USGS have developed social science tools and research 

methods to support land management planning and decisionmaking; they 

have been applied in the Borderlands and on public lands throughout the 

Nation. Specific abilities include (1) surveying visitors, community

residents, and other stakeholders about their activities on public lands 

and their attitudes, perceptions, and knowledge of management 

alternatives; (2) understanding the relations among public land 

management, human well-being, and community sustainability 

in light of phenomena such as climate change, energy 

development, and flooding; and (3) measuring public and

decisionmaker perceptions of risk regarding human hazards. 

Researchers with the USGS apply traditional and state-of-the-art 

social science methods drawing from the fields of sociology,

demography, economics, political science, communications, 

social-psychology, and applied industrial organization psychology. 

Our social science methods work in concert with our natural 

science capabilities.
Challenge Theme 4. People in the Borderlands 153

In the unique context of the Borderlands, the USGS has the capability to use social science 

methods to understand the vulnerability and resilience of human communities within the context 

of global/climate change, facilitating the stability and sustainability of human communities 

(Norman, Villarreal, and others, 2012). We are also capable of working collaboratively with 

Native American nations in the areas of education, natural resources, and development of 

sustainable capabilities. Assistance in the preservation of cultural resources can be a cornerstone 

of that collaboration. Remote sensing, geospatial derivative maps of special areas, corridor map 

products, relational databases, and ground-based GPS-supported land surveys can assist Federal 

and Native American planners, enforcement officials, and decisionmakers (Hall and others,

2010; Tallent-Halsell and others, 2010).

Finally, the USGS can facilitate decisionmaking concerning complex problems with 

multiple stakeholders, integrating multiple forms of scientific data in difficult situations. We

have experience in applying decisionmaking techniques such as decision analysis adaptive 

management, joint fact-finding, decision support, and stakeholder analysis (Norman, 

Tallent-Halsell, and others, 2010).

References cited in this chapter are listed in chapter 12.
Challenge Theme 5. Current and Future 

Needs of Energy and Mineral Resources 

in the Borderlands and the Effects of 

Their Development

By Floyd Gray, William R. Page, Peter D. Warwick, and Martín Valencia-Moreno

Introduction

Exploration and extraction activities related to energy and 

mineral resources in the Borderlands—such as coal-fired power plants, 

offshore drilling, and mining—can create issues that have potentially 

major economic and environmental implications. Resource assessments 

and development projects, environmental studies, and other related 

evaluations help to understand some of these issues, such as power 

plant emissions and the erosion/denudation of abandoned mine lands. 

Information from predictive modeling, monitoring, and environmental 

assessments are necessary to understand the full effects of energy and 

mineral exploration, development, and utilization. The exploitation of 

these resources can negatively affect human health and the environment, 

its natural resources, and its ecological services (air, water, soil, 

recreation, wildlife, etc.). This chapter describes the major energy 

and mineral issues of the Borderlands and how geologic frameworks, 

integrated interdisciplinary (geobiologic) investigations, and other 

related studies can address the anticipated increases in demands on 

natural resources in the region.

Chapter 7
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 155

Lavender Pit copper mine near Bisbee, Arizona
156 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Porphyry Copper Resources

Copper is the most economically important mineral resource in the Borderlands. It occurs 

dominantly as porphyry copper systems: copper orebodies that are associated with intrusive

rocks and the fluids that accompany them during the transition and cooling from magma to

rock. These copper deposits occur along a belt oriented northeast-southwest, exposed along 

most of the western edge of North America. About 15 major deposits have been recognized in 

this belt, and almost all are located in the Borderlands. The combined large deposits of southern 

Arizona, western New Mexico, and northwestern Mexico constitute one of the most prominent 

copper provinces on Earth (fig. 7–1) (Titley, 1993). This province, commonly referred to as the

“great cluster” of porphyry copper deposits of Arizona, Sonora, and New Mexico (Keith and 

Swan, 1996), includes about 12 economically important mines, some of which have been 

Aerial view of the 

Cananea copper mine, Sonora
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 157

classified as being of giant size (greater than 2.5 million metric tons copper [2.8 million short

tons]; Clark, 1993; Laznicka, 1999). The most productive locations, which are considered to 

be of global importance, are the Safford and Morenci deposits in Arizona and the Cananea and 

La Caridad deposits in northeastern Sonora (fig. 7–1). The importance of these deposits is

shown by the fact that approximately 60 percent of all copper production in the United States 

and 95 percent of all copper production in Mexico comes from the Borderlands. In addition, 

production from the border region of Mexico represents approximately 3.3 percent of all 

porphyry copper produced in the world and 18.1 percent of the potential estimated for the 

“great cluster” (fig. 7–1). The majority of occurrences south of this rich province are of

marginal importance.
1

2

3 4

5

6

7

8

TEXAS

CALIFORNIA ARIZONA NEW MEXICO

SONORA

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA UNITED STATES 

MEXICO

PACIFIC

OCEAN

Gulf

of

Mexico

Gulf of California

Hermosillo

Tucson

La Caridad

Cananea

Bisbee

Chino

Morenci

Miami Inspiration

Ray

Mission

Sierrita

San

Manuel

Safford

110°

30°

100°

105°

115°

25°

0 125 250 KILOMETERS

0 125 250 MILES

EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

International boundary

So-called “great cluster” of the porphyry belt

Major copper deposit (unnamed)

Major copper deposit (named)

1

United States

Arizona–New Mexico: 81.93 percent

Mexico

Cananea deposit: 12.5 percent

La Caridad deposit: 3.4 percent

Rest of the Mexican belt: 2.2 percent

EXPLANATION

South American western cordillera: 

 45.4 percent

Rest of the world: 24.6 percent

North American western cordillera

Mexico: 3.3 percent

Arizona–New Mexico: 14.8 percent

Rest of the cordillera: 11.9 percent

EXPLANATION

South American

western cordillera:

45.4 percent

Rest of the

cordillera:

11.9 percent

Arizona–

New Mexico: 14.8 percent

Arizona–New Mexico:

81.93 percent

Rest of the world:

24.6 percent

Mexico:

18.1 percent

North American western cordillera:

30 percent

Mexico:

3.3 percent

MEXICO

MEXICO

“Great Cluster” Copper Resources:

240 million metric tons of copper

“Great Cluster” Copper Resources

World Copper Resources:

1,336 million metric tons of copper

1

2

3 4

5

6

7

8

TEXAS

CALIFORNIA ARIZONA NEW MEXICO

SONORA

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA UNITED STATES 

MEXICO

PACIFIC

OCEAN

Gulf

of

Mexico

Gulf of California

Hermosillo

Tucson

La Caridad

Cananea

Bisbee

Chino

Morenci

Miami Inspiration

Ray

Mission

Sierrita

San

Manuel

Safford

110°

30°

100°

105°

115°

25°

0 125 250 KILOMETERS

0 125 250 MILES

EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

International boundary

So-called “great cluster” of the porphyry belt

Major copper deposit (unnamed)

Major copper deposit (named)

1

United States

Arizona–New Mexico: 81.93 percent

Mexico

Cananea deposit: 12.5 percent

La Caridad deposit: 3.4 percent

Rest of the Mexican belt: 2.2 percent

EXPLANATION

South American western cordillera: 

 45.4 percent

Rest of the world: 24.6 percent

North American western cordillera

Mexico: 3.3 percent

Arizona–New Mexico: 14.8 percent

Rest of the cordillera: 11.9 percent

EXPLANATION

South American

western cordillera:

45.4 percent

Rest of the

cordillera:

11.9 percent

Arizona–

New Mexico:

14.8 percent

Arizona–New Mexico:

81.93 percent

Rest of the world:

24.6 percent

Mexico:

18.1 percent

North American western cordillera:

30 percent

Mexico:

3.3 percent

MEXICO

MEXICO

“Great Cluster” Copper Resources:

240 million metric tons of copper

“Great Cluster” Copper Resources

World Copper Resources:

1,336 million metric tons of copper

copper

158 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 159

Figure 7–1. Map (left) and comparative charts (right) of the 

porphyry copper–rich region of the southern United States 

and northwestern Mexico. The map shows the “great cluster” 

of porphyry copper deposits in the western cordillera of North 

America (shaded area) and the location of individual deposits. 

The most significant deposits are named. The charts show 

Mexican porphyry copper resources in the context of the “great 

cluster” (top) and compared to world resources (bottom). 

Modified from Valencia-Moreno and others (2007); chart data 

estimated from data in Singer and others (2003).
The mid-1800s marked the beginning of a long and colorful history of 

mining in the western United States and Mexico. That history left a legacy of 

approximately 11,000 abandoned hard-rock mine sites. At many of these sites, 

historical mining activities—including random dumping, unfiltered smelter 

emission, and unrestricted metal-laden tailings leachate—resulted in adverse 

effects on the quality of water and sediment and on the health of humans 

and other biota. For example, the Cananea Consolidated Copper Company 

has operated a copper smelter in Cananea in Sonora, Mexico, since the late 

1800s. Today, Cananea is a densely populated urban environment whose 

economy is based on the copper smelting industry. It is the copper capital of 

Mexico, but atmospheric pollution from the smelter degrades the quality of 

the local environment.

Understanding the processes that influence the distribution, concentration, 

and bioavailability of potentially toxic metallic elements is critical for the 

successful management of chronically affected ecosystems where the total 

remediation of environmental problems is not economically feasible. The USGS 

is coordinating with the Mexican government and other Federal agencies to 

ensure all of the issues of this ongoing problem are taken into account.

Metals Transport from Abandoned 

Mine Lands, Smelter Emissions, 

and Metal Solute Migration in 

Groundwater

. . . .facing the challenge
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 161

The town of Cananea in Sonora (left) is the copper capital of Mexico and home to the Cananea 

Consolidated Copper Company. Note the number of stacks in operation in the early 1900s (top) and 

the single main stack operating in 2007 (bottom). The smelter stack has since been torn down.

then

now

Circa 1906–1910

Circa 2007
162 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Other Mineral Deposits and Resources

Mexico is one of the world’s largest producers of silver, much of which is imported across 

the border to the United States, but the most significant deposits are in the southern Mexican

states, including Zacatecas, far from the Borderlands. For gold and silver, the distribution of 

major mines, prospects, and occurrences indicates that both placer and lode deposits were 

mined historically in the Borderlands (fig. 7–2). Precious metals, such as gold and silver, were

the dominant commodities of interest in the Borderlands until the mid-19th century, when lead, 

zinc, and copper deposits began to be mined, eventually dominating metal production in the 

region. The distribution of precious metals indicates the western part of the area is richer in 

gold and the southeastern part of the area is richer in silver. There are no reported major gold 

occurrences in Nuevo León, Tamaulipas, or Coahuila, Mexico, although a few small occurrences 

have been reported. Figure 7–2 also shows the distribution of known mines, prospects, and 

occurrences where copper, lead, and zinc are the main commodities; most of these locations 

have since been abandoned. Lead and zinc deposits appear to be more abundant in the eastern 

part of the Borderlands, particularly in Chihuahua, Coahuila, and Tamaulipas. The level of 

ongoing modern exploration indicates that the Borderlands will continue to be a source of 

considerable wealth in precious metals in the foreseeable future (Orris and others, 1993).

In addition to precious and base metals discussed above, other mineral commodities are 

produced in the Borderlands (table 7–1). The Mexican cement company CEMEX (formerly 

Cementos Mexicanos) is one of the three largest cement producers in the world. Mexico is a 

major supplier of cement for the United States and has major limestone mining and processing 

operations along the border, such as those in and around the El Paso–Ciudad Juárez sister city 

area (Texas-Chihuahua).
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 163

Metals

Major Minor

Copper

Gold

Lead

Silver

Zinc

Iron

Mercury

Molybdenum

Rhenium

Tungsten

Industrial Minerals and Materials

Major Minor

Aggregate (crushed stone and gravel)

Barite

Bentonite 

Borates

Celestite

Clays

Fluorite

Graphite (amorphous)

Gypsum

Halite

Limestone (for use in cement)

Potash

Pumice

Sand and gravel

Sodium sulfate (natural)

Sulfur

Zeolites

Building stone

Diatomite

Feldspar

Kaolin

Magnesia-magnesite

Mica

Nitrogen-nitrates

Perlite

Phosphates

Wollastonite

Table 7–1. Mineral commodities produced in the United States–Mexican border region. Data from 

the Mineral Resources Data System (http://tin.er.usgs.gov/mrds/ ).
Silver and Gold Resources

Copper, Lead, and Zinc Resources

1

2 3

4

5

6

7

8

1

2

3 4

5

6

7

8

TEXAS

CALIFORNIA

CALIFORNIA

ARIZONA

NEW MEXICO

SONORA

CHIHUAHUA

COAHUILA

TAMAULIPAS

NUEVO

LEÓN

BAJA

CALIFORNIA

BAJA

CALIFORNIA

TEXAS

ARIZONA

NEW MEXICO

SONORA

CHIHUAHUA COAHUILA

TAMAULIPAS

NUEVO

LEÓN

UNITED STATES 

MEXICO

UNITED STATES 

MEXICO

PACIFIC

OCEAN

Gulf

of

Mexico

Gulf of California

PACIFIC

OCEAN

Gulf

of

Mexico

Gulf of California

95°

100°

110° 105°

115°

120°

40°

35°

30°

25°

95°

100°

110° 105°

115°

120°

40°

35°

30°

25°

0 125 250 175 500 KILOMETERS

0 125 250 375 500 MILES

Figure 7–2. Distribution of major mines, prospects, and occurrences for silver and gold 

(top) and copper, lead, and zinc (bottom) in and adjacent to the United States–Mexican border 

region. Modified from Orris and others (1993); data from the Mineral Resources Data System 

(http://tin.er.usgs.gov/mrds/).
EXPLANATION

Subareas of the border region

1 Pacific Basins–Salton Trough

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

5 Rio Grande West—Elephant Butte Reservoir to Rio Conchos

6 Rio Grande Central—Rio Conchos to Amistad Reservoir

7 Rio Grande East—below Amistad Reservoir to Falcon Reservoir

8 Lower Rio Grande Valley

International boundary

Silver and gold resources

Silver

Gold

Silver and gold

Copper, lead, and zinc resources

Copper

Lead and (or) zinc

Copper and lead and (or) zinc

1

Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 165

copper

gold

silver

lead

zinc
The Patagonia 

Mountains and southern 

Santa Rita Mountains in 

southeastern Arizona 

were mined for silver, 

lead, copper, and zinc 

intermittently from the 

1600s to the mid-1960s. 

Studies carried out by 

the USGS in the Harshaw 

Creek and Alum Gulch 

watersheds examined 

the transport and 

chemical behavior of 

metals in several arid 

to semiarid watersheds 

containing these 

abandoned mine lands 

(see Balistrieri and 

others, 2007) with the 

goal of evaluating how climate and other conditions influence metal cycling 

in mining-affected ecosystems. Such knowledge is vital for developing robust 

models that describe the potential effects on the environment of mining activity 

in different climate settings.

Seasonal precipitation and acid mine drainage, which contains dissolved 

metals such as cadmium, cobalt, copper, nickel, lead, and zinc, are the 

dominant sources of water to a variety of downstream habitats. During dry 

periods, acid rock drainage evaporates and readily soluble metal sulfate salts 

are deposited on rocks and in stream sediment. During storm events, these 

salts dissolve and release acid and metals back into solution. Downstream 

decreases in acid and metal concentrations after a storm event depend on 

the ability of the ecosystems to neutralize or buffer the acid produced during 

salt dissolution and on the volume of water from the storm event. If the buffering 

capacity of the ecosystem is small, acid and metals are transported far 

downstream in the dissolved phase. If the ecosystem has large buffering 

capacity, neutralization results in the precipitation of aluminum-iron-oxyhydroxide 

minerals, adsorption of metals, and release of carbon dioxide gas.

Acid Mine Drainage in the 

Patagonia Mountains

Iron-stained acid rock drainage (left side of image) converging 

with a neutral stream. 

. . . .facing the challenge
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 167

Apart from the complex biogeochemical processes affecting dissolved 

metals at near-neutral pH in degraded, semiarid watersheds in the Southwest, 

stormflow causes significant transport of aluminum, iron, zinc, copper, cadmium, 

and uranium associated with suspended aluminum-iron-oxyhydroxides and 

oxyhydroxysulfate minerals. The settling of suspended particles and precipitates 

in streams may result not only in the introduction of metal toxins to the streambed 

sediments but also in changes in the phototropic levels and in the amount of 

oxygen available to bottom-dwelling organisms and fish species.

Currently, there are knowledge gaps concerning the bioavailability of 

metals from streambed/soils, the mineralogy and speciation of metals, and the 

remobilization potential of adsorbed or precipitated metals associated with 

suspended solids under a variety of conditions in arid to semiarid regions. 

A major outcome of our research has been an improved understanding of the 

connections among weather conditions, landscape, mineral precipitation and 

dissolution, and metal transport. The U.S. Forest Service and the Arizona 

Department of Environmental Quality (http://www.azdeq.gov/) use this information 

to develop remediation plans for this mining-affected area.
168 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Energy Resources

The Borderlands have plentiful energy resources used 

primarily for power generation (fig. 7–3). These resources

include conventional oil and natural gas, offshore natural gas 

hydrates, coal and coalbed methane, oil sands, and uranium 

(Masters and others, 1998; USGS World Energy Assessment 

Team, 2000; Dyni, 2003; Dubiel and others, 2007, 2011; 

Meyer and others, 2007; Tewalt and others, 2008). Though 

it would be inaccurate to characterize Mexico as energy rich, 

it by no means lacks energy resources. About 92 percent of the 

country’s energy needs are met through hydrocarbon sources 

(oil, gas, and coal) and about 8 percent through hydroelectric, 

nuclear, and renewable energy generation (U.S. Energy 

Information Administration, 2011). Nuclear, geothermal, wind, 

and solar energy are minor contributors to an economy with 

growing energy demands.
SONORA

CHIHUAHUA

DURANGO

SINALOA

ZACATECAS

COAHUILA 

TAMAULIPAS

NUEVO

LEÓN

SAN LUIS

POTOSI

BAJA

CALIFORNIA

SUR

BAJA

CALIFORNIA

TEXAS

ARIZONA

NEW MEXICO

OKLAHOMA

CALIFORNIA

PACIFIC OCEAN

Gulf of Mexico

Gulf of California 

UNITED STATES 

MEXICO

0 100 200 300 400 500 MILES

0 100 200 300 400 500 KILOMETERS

EXPLANATION

Geothermal energy

Oil sands

Coal and coalbed methane

Natural gas hydrates

Conventional oil and gas

Conventional oil and gas

 and Uranium provinces

 Uranium provinces

International boundary

115° 110° 105° 100° 95°

35°

30°

25°

Figure 7–3. Potential energy resources along the United States–Mexican border. For potential areas for solar and wind energy 

development in the western United States–Mexican border region, see fig. 10–6. Compiled from Masters and others (1998), USGS World 

Energy Assessment Team (2000), Dyni (2003), Meyer and others (2007), and Tewalt and others (2008).

Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 169

Conventional oil and natural gas resources in Texas have been exploited since the late 1800s, and the Texas oil boom of the 

early 20th century gave the state status as the leading oil producer in the Nation. Texas has produced more oil and natural gas 

than any other state to date; it remains the country’s largest daily producer, and its refineries remain the most active in the United

States. Natural gas production in Texas peaked in the 1970s, and production has remained steady because of increases in the 

number of producing wells, which are at an all-time high. In fact, most new exploration and production activities in Texas are 

related to natural gas, not oil.

The greatest potential petroleum resource in the Borderlands is the Burgos Basin province along the northeast border 

of Mexico in Tamaulipas and Nuevo León, south of Texas (fig. 7–4). The most recent U.S. Geological Survey (USGS)

assessments of the hydrocarbon resources of the Burgos Basin (Schenk and others, 2004) give estimates of 20 trillion cubic feet 

of natural gas, 6.2 billion barrels of oil, and 0.52 billion barrels of natural gas liquids (0.57 trillion, 0.99 billion, and 0.08 billion 

cubic meters, respectively). Obviously, development of this basin will critically affect the economy and environment in the 

eastern Borderlands.
TEXAS

TAMAULIPAS

NUEVO LEÓN

COAHUILA

37

35

77

281

77

57

85

85

81

57

101

Saltillo

Monterrey

Ciudad 

Victoria

Laredo

Corpus Christi

MEXICO

STATES

UNTIED

Brownsville

Gulf of Mexico

Burgos Basin 

Province Mexican Ridges

Tampico-Misantla Basin

Perdido

Fold Belt

Tamaulipas Arch

Peyote-Picachos Arches

El Burro–Salado Uplifts

Rio San Fernando 

Rio San Juan

Rio Salado

RIO GRANDE

RIO BRAVO

102° 100° 98° 96° 94°

26°

24°

28°

0 60 KILOMETERS 30

TEXAS 0 30 60 MILES

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

7

8

Figure 7–4. Burgos Basin province of northeastern Mexico. 

Modified from Schenk and others (2004).

170 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Commercial coal mining in Texas began in the 1880s, and most of the coal resources in the Borderlands are in an area 

extending southward from the Eagle Pass–Piedras Negras sister city area (Texas-Coahuila) to the Laredo–Nuevo Laredo sister 

city area (Texas-Tamaulipas). Most coal in Texas is lignite, but some bituminous coal is mined in the Piedras Negras area. The 

coal is used principally for steam generation at nearby power plants. All of Mexico’s coal reserves are in northern Coahuila, 

located near the state’s major coal-burning power plants in Piedras Negras, Coahuila. Because Mexico does not produce sufficient

amounts of coal to meet its smelting and power demands, the rest of the country’s coal needs are met through imports, primarily

transported from the United States by train. Recent investigations by the USGS and others have identified coalbed methane

resources in basins that span or are near the Borderlands in southeastern Texas and northeastern Mexico (Barker and others, 

2003; Eguiluz de Antuñano and Amezcua Torres, 2003; Warwick and others, 2007, 2011).

Uranium resources have been mined in the South Texas uranium district since the 1960s. The closest uranium mines to the 

Borderlands are in Karnes County, Tex., about 60 kilometers (37 miles) southeast of San Antonio, but uranium-bearing rock 

formations extend southward to the border and into northern Mexico (Bureau of Economic Geology, 1981). Uranium mining 

increased in the district in the 1970s, but production dropped off after 1980 because of decreased demand and price. Today, most 

uranium resources in Texas are produced from in-place mining operations.
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 171
172 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Energy and Mineral Resource Issues

Land managers and government officials in the Borderlands are continually faced with decisions that involve the supply

and use of raw materials, the substitution of one resource for another, competing land uses, and the environmental consequences 

of resource development. Informed planning and decisionmaking processes require integrated information from a broad area. 

To help supply some of the information necessary to this approach, the USGS collaborates with cooperators in unbiased, 

accurate scientific assessments of undiscovered energy and mineral resources based on knowledge of identified resources and

an understanding of the processes that influence the distribution, concentration, and bioavailability of potentially toxic elements.

For Federal, State, and local agencies charged with minimizing the effects of toxic elements on human health and the environment, 

investigations carried out in this way provide the scientific foundation needed to make decisions, develop strategy, and assess

mitigation and remediation alternatives (Balistrieri and others, 2007).
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 173

After more than a century of industrialization, agriculture, and urbanization as a significant source and processing area for

the Nation’s energy and mineral needs, the Borderlands have a legacy of disturbed land—much of it damaged prior to the 

regulatory oversight of the mid to late 20th century. The mineral and fuel deposits in the Borderlands, however, remain important 

to domestic and international users, so interaction with resources still plays a potentially key role in the geoenvironmental 

status of the area. Geologic studies are crucial in understanding the issues associated with the thousands of abandoned mines 

on Federal lands, such as the effects of metals dispersion in air and water and the occurrences and cycles of toxins and pathogens 

in soils (see the USGS Abandoned Mine Lands Initiative, http://amli.usgs.gov/). Geologic research in these areas develops 

precision techniques and instrumentation used to identify sources of contamination and the processes that interact to create the 

biogeochemical cycles that ultimately affect human and habitat health. An important example of environmental effects of past 

mining activities in the Borderlands is the ASARCO1

 metals smelter in El Paso, Tex., where the U.S. Environmental Protection 

Agency is currently investigating soil contamination in the smelter area and planning future clean-up operations in populated 

neighborhoods adjacent to the smelter. The smelter processed lead and copper from Arizona and the western United States until 

the 1990s. Other metal smelters historically were active in the Borderlands, such as the Cananea copper smelter in northern 

Sonora, Mexico, and smelters in the Laredo, Texas, area. Several other examples of the effects of past mining activities in Arizona 

and Sonora are discussed in the “. . . .facing the challenge” sections on pages 160–161 and 166–167.

1 Formerly the American Smelting and Refining Company.

Mining in Bisbee, Arizona, 

1902

ASARCO copper smelting plant
174 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Although energy resources (coal, oil, and natural gas) are the foundation for modern

industrial society, aspects of the extraction, processing, and utilization of these resources can

potentially impair human and wildlife health. For example, energy resources can contain

chemical substances that, if mobilized into air, water, and soil, can be harmful to humans and

wildlife. Toxic substances from coal found in some water supplies in areas of southeastern 

Europe have been connected to kidney disease and cancer (Orem and others, 2010), and

coal-fired power plants in Texas and Coahuila release large amounts of CO2, which increase

rates of greenhouse gas emissions and thus contribute to climate change and global warming.

Coal-burning plants are also major point sources in the Borderlands (Martinez and Deshpande,

2009) for emissions of particulate matter that includes toxic mercury and arsenic. Chemical

plants, petroleum refineries, and oil and gas production facilities in southern Texas and northern

Mexico can introduce harmful substances into the environment, including volatile organic 

compounds, polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), 

sulfur dioxide, benzene, and toluene. The recent Deepwater Horizon oil spill in the Gulf of 

Mexico (http://www.usgs.gov/oilspill) exemplifies the vulnerability of Borderlands society and

its economy and ecosystems to similar potential disasters in the Tamaulipas and Texas coastal 

areas of the Borderlands. 
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 175

Fire boat crews responding to the blaze on the Deepwater Horizon offshore rig

Areas of dark brown and red emulsion oil near the convergence 

zone of the Deepwater Horizon oil spill, May 2010
176 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

 USGS Capabilities

The USGS is currently engaged in several projects that have the potential to respond to the growing need for international 

mineral information, such as the evaluation of concealed mineral deposits, the geoenvironmental modeling project, and the 

Global Mineral Resource Assessment Project. In addition, the existing project objectives can be tailored to integrate and coordinate 

with the regional and binational aspects of the Borderlands.

Because the Borderlands host several world-class mineral belts, its ability to supply many basic minerals to industries 

within and outside of its boundaries contributes to the prospect of a dynamic economic future for the region. Initial compilation 

of nonfuel mineral resource data—precious metals, base metals, and mineral commodities used in infrastructure, agriculture, 

and environmental improvement—yields approximately 9,300 known deposits and occurrences in the Borderlands. In the near 

future, with increased demand for metals and hence higher commodity prices, the exploration for and exploitation of mineral 

deposits are likely to experience significant growth. Preliminary assessment of the geological terranes indicates that further

exploration in northern Mexico could augment the known deposits of many metallic and industrial minerals, including copper, 

silver, zeolites, and clays, as well as aggregate, sand, and gravel.

Silver Bell mine, Arizona
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 177

The USGS already has carried out assessments of the undiscovered but technically recoverable oil and gas resources 

throughout the United States Gulf Coast and northeastern Mexico (Schenk and Viger, 1995 a, b; USGS World Energy Assessment 

Team, 2000; Pollastro and others, 2001; Schenk and others, 2004; Condon and Dyman, 2006; Dyman and Condon, 2006; Dubiel 

and others, 2007; Pittman and others, 2007; Warwick and others, 2007). These assessments are based on geologic elements such 

as the presence of hydrocarbon source rocks, suitable reservoir rocks, and hydrocarbon traps within the total petroleum systems 

identified in the region. Assessment of undiscovered oil and gas potential in basins in the Borderlands is necessary to understand

the potential contribution of Mexican resources to the North American gas supply (Schenk and others, 2004). In 2004, a USGS 

assessment of the Burgos Basin in northeastern Mexico (fig. 7–4) was undertaken to understand this basin’s potential contributions

to the regional gas supply (Schenk and others, 2004); detailed oil and gas assessments of other basins in Mexico have also been 

reported (Schenk, 2012). Recent assessments of geothermal energy resources (Williams and others, 2008) and ongoing 

investigations into offshore natural gas hydrates (National Energy Technology Laboratory, 2008) and uranium resources (USGS 

Energy Resource Program, 2008) will add to a better understanding of the energy resource base in the Borderlands.

English Español
178 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

On the environmental side of oil and gas production, the USGS is playing a critical role 

in assessing the effects of the Deepwater Horizon oil spill, and it continues to gather scientific

data on the environmental effects of the spill on nearby coastal habitats. In the days after the 

spill, USGS scientists responded by collecting samples from Texas, Louisiana, Mississippi, 

Alabama, and Florida before the oil could make landfall in order to establish baseline conditions 

for water chemistry, bottom sediments, and aquatic invertebrates. They also collected samples 

from barrier islands and coastal wetlands; these areas are critical to fish and wildlife in the

Gulf of Mexico and could have suffered severe environmental damage had oil from this spill 

come ashore. 

In addition, USGS scientists collected satellite imagery to assess the spill’s effects on 

wetlands and coasts, developed maps showing projections by the National Oceanic and 

Atmospheric Administration of spill trajectory with respect to lands owned by the U.S. 

Department of the Interior (DOI), collected 

samples to ascertain source and levels of 

toxicity to soils and water systems, conducted 

tests to determine cause of mortality of 

wildlife, and developed models that depict 

how local tidal and current conditions interact 

with seafloor bathymetry to carry oil over

barrier islands. Many of these projects are 

ongoing. The USGS also provides decision 

support tools to land managers with the DOI 

to help mitigate the effects of the oil spill and 

assist in restoration efforts.

References cited in this chapter are listed 

in chapter 12..

U.S. Geological Survey 

scientist collecting sediment 

core samples on the Gulf Coast 

in response to the Deepwater 

Horizon oil spill, October 2010
Challenge Theme 5. Current and Future Needs of Energy and Mineral Resources in the Borderlands 179
Challenge Theme 6.

Natural Hazard Risks in the Borderlands

By William R. Page, Jean W. Parcher, and Jim Stefanov

Introduction

Natural hazards such as earthquakes, landslides and debris flows, 

wildfires, hurricanes, and intense storm-induced flash floods threaten 

communities to varying degrees all along the United States–Mexican 

border. The U.S. Geological Survey (USGS) collaborates with Federal, 

State, and local agencies to minimize the effects of natural hazards by 

providing timely, unbiased science information to emergency response 

officials, resource managers, and the public to help reduce property 

damage, injury, and loss of life. The USGS often mobilizes response 

efforts during and after a natural hazard event to provide technical 

and scientific counsel on recovery and response, and it has a long 

history of deploying emergency response teams to major disasters in 

both domestic and international locations. This chapter describes the 

challenges of natural hazards in the United States–Mexican border 

region and the capabilities of the USGS in the fields of hazard research, 

monitoring, and assessment, as well as preventative mitigation and 

post-disaster response.

Chapter 8

(Facing page) La Conchita landslide, Ventura County, California, 2005
Challenge Theme 6. Natural Hazard Risks in the Borderlands 181
Damage to shops and telephone 

lines in Imperial, California, 

caused by the 1940 earthquake

182 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Earthquake Hazards

Earthquakes can occur at any time without warning and can have dire consequences, including damage to buildings and 

infrastructure, economic disruption (both locally and regionally), and loss of life. Earthquake damage to infrastructure—such as 

pipelines, wastewater treatment plants, power plants, and chemical storage facilities—can release contaminants that can cause 

long-term negative effects on ecosystems and natural resources.

The area along the border most susceptible to earthquakes and associated hazards (ground shaking, liquefaction, landslides, 

etc.) is southern California and northern Baja California (fig. 8–1). Earthquakes in this region have occurred along several

northwest-striking fault zones including the Imperial, Laguna Salada, and Cerro Prieto fault zones (fig. 8–2), which are part of

the San Andreas transform fault system. A magnitude 7.1 earthquake along the Imperial fault zone in 1940 bent rail lines, 

severely damaged irrigation canals, and killed nine people in what was then a very sparsely populated Imperial Valley; a similar 

event today would be far more costly in loss of property and loss of life. Because earthquakes affect populations on both sides 

of the border, as illustrated by the magnitude 7.2 El Mayor–Cucapah earthquake in 2010 that caused major damage in northern 

Baja California, the need for coordinated and cooperative efforts between United States and Mexican agencies is imperative.

Furrows in a plowed field offset 

by the 1979 Imperial Valley, 

California, earthquake

1940

1979
Lowest

hazard

Highest

hazard

Earthquake hazard

Partial collapse of four columns of the Imperial County Services 

building in El Centro, California, during the 1979 Imperial Valley, 

California, earthquake

Challenge Theme 6. Natural Hazard Risks in the Borderlands 183

Figure 8–1. U.S. Geological Survey National Seismic Hazard 

Map showing expected levels of strong earthquake shaking likely 

to occur within the next 50 years. Pink colors define areas where 

ground shaking is expected to be strongest, while white colors are 

areas where ground shaking is likely to be minimal. Note that the 

border region along southern California ranks among the areas 

with the highest hazard expectations in the continental United 

States. (Map as of 2008 update.)

1979

earthquakes
Damage to a bowling alley in 

Yucca Lake, California, caused 

by the 1992 Landers earthquake

Surface rupture from the 2010 El Mayor-Cucapah earthquake, Baja California

184 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

1992

2010
UNITED STATES

MEXICO

ARIZONA

CALIFORNIA

SONORA

BAJA CALIFORNIA

Gulf of California

Salton Sea

COLORADO RIVER

Gila River

Santa Clara

San Luis

Yuma

SAN ANDREAS FAULT

ALTAR FAULT

ALTAR FAULT

CERRO PRIETO FAULT

IMPERIAL FAULT

LAGUNA SALADAL FAULT

Imperial Valley

Altar Basin

Sierra Juárez

Sierra de Los Cucapahs

Sierra El Mayor

Sierra de Las Tinajas

Sierra El Rosario

Mexicali Valley

Modified from Pacheco and others, 2006

116° 115° 114°

33°

32°

0 50 KILOMETERS

50 MILES

25

0 25

EXPLANATION

International boundary

Fault—Dashed where inferrred; 

 arows show relative movement

Epicenter for 2010 El Mayor–Cucapah earthquake

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

1

2

Challenge Theme 6. Natural Hazard Risks in the Borderlands 185

Figure 8–2. Major active faults along the United States–Mexican border in California and Baja California and the location of the 2010 

El Mayor–Cucapah earthquake. Modified from Pacheco and others (2006).
On the afternoon of April 4, 2010, a magnitude 7.2 earthquake struck in 

northern Baja California approximately 60 kilometers (37 miles) south of the 

United States–Mexican border. The El Mayor–Cucapah earthquake occurred 

on the Laguna Salada fault (fig. 8–2) in an area of historical seismicity, though 

this was the largest event to strike in the area for over a hundred years. 

Because the energy release was shallow and extended over several tens of 

kilometers, the earthquake produced complex surface ruptures and severe 

damage was sustained in nearby populated areas, including Mexicali in Baja 

California. Earthquakes can disrupt transportation and critical lifeline 

infrastructure, as well as fuel and gas lines, high-tension power lines, and 

fiber optic communication lines. Because of the severity of damage and 

frequency of aftershocks, many inhabitants from Mexico were fleeing to the 

United States border at Calexico, Calif., for perceived sanctuary, while at 

the same time inhabitants from the United States were attempting to cross 

the border into Mexico to support relatives to the south. This flood of people 

on foot at the border eventually forced the closure of the crossing.

2010 El Mayor–Cucapah 

Earthquake, Baja California, 

Mexico 

For more information on the earthquake and to download this poster, see http://earthquake.usgs.gov/

earthquakes/eqarchives/poster/2010/20100202.php.

. . . .facing the challenge
Challenge Theme 6. Natural Hazard Risks in the Borderlands 187

U.S. Geological Survey ShakeMap for 2010 El Mayor–Cucapah earthquake. For more information on 

ShakeMaps, see http://earthquake.usgs.gov/earthquakes/shakemap.

The area is traversed by a series of northwest-trending strike-slip faults 

parallel to the southern extent of the San Andreas fault, and field geologists 

from Mexico and the United States have subsequently been able to map a 

pronounced and complex rupture at the earth’s surface with displacements 

in excess of a meter (Rymer and others, 2011). Working with regional seismic 

network partners, the USGS was able to transmit automated information 

on the El Mayor–Cucapah earthquake within 10 minutes of the mainshock 

through its National Earthquake Information Center and ShakeMap program.

(Continued on page 188)
. . . .facing the challenge
TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

1

2

Surface fault ruptures from the 2010 El Mayor–Cucapah earthquake 

breaking through an abandoned highway west of Mexicali, 

Baja California, Mexico
Figure 8–3. Debris flows in Sabino Canyon in the Santa Catalina Mountains, Arizona, caused by 

record flooding after extreme convective thunderstorms, July 2006.

190 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Landslides and Debris Flows

Landslides cause billions of dollars in damage and dozens of fatalities each year in the 

United States. Often the loss of life and property is due to the fact that our homes, businesses, 

and transportation routes are frequently located in areas that are geologically prone to slope 

instability. A combination of natural and manmade events in series can greatly increase slope 

instability, and because much of the Borderlands are located in an arid to semiarid climate zone 

with sparse vegetation and shallow soils, the region is especially at risk for landslide and debris 

flow events. Heavy precipitation following other natural phenomena, such as an earthquake,

wildfire, or flood, might trigger landslides and debris flows. For example, extreme convective

thunderstorms in July 2006 caused 250 hillslope failures and debris flows in the Santa Catalina

Mountains north of Tucson, Arizona (Magril and others, 2007). In Sabino Canyon, a heavily 

used recreation area managed by the U.S. Forest Service, debris flows destroyed roads and

removed structures, necessitating the closure of the area for several months (fig. 8–3) (Magril

and others, 2007). These same storms also caused debris flows in Coronado National Memorial,

Ariz., where flows buried sections of Montezuma Canyon Road, the memorial’s major road,

and debris and mud filled picnic areas (fig. 8–4).

landslides
Figure 8–4. Heavy equipment was used to clear debris flows on Montezuma Canyon Road in 

Coronado National Memorial, Arizona, July 2006.

Laguna Beach landslide, California, 2005

Challenge Theme 6. Natural Hazard Risks in the Borderlands 191
EXPLANATION

Wildfire greater than 250 acres, 1980−2003

192 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Wildfires

Wildfires are an escalating natural hazard in all parts of the United States (fig. 8–5) and are

significant threats to life and property, particularly where the urban fringe encroaches on native

ecosystems. Wildfires are prevalent and dangerous phenomena in the Borderlands, where

they are enhanced by frequent strong winds, arid conditions, and dry vegetation. The primary 

effects of wildfire are the destruction of community infrastructure and cultural and economic

resources and the loss of life; the destruction of timber, forage, wildlife habitats, scenic vistas, 

and watersheds; and the release of hazardous material and the pollution of air, water, and soil. 

In the Borderlands, secondary effects include an increased potential for flooding, debris flows,

and landslides; increased erosion; introduction of invasive species; changes in water quality; 

and reduced access to recreational areas.

Figure 8–5. Locations of wildfires covering 250 acres or greater 

that occurred in the United States between 1980 and 2003. 

Information from the U.S. Geological Survey, Bureau of Land 

Management, U.S. Forest Service, U.S. Fish and Wildlife Service, 

Bureau of Indian Affairs, and National Park Service. Modified 

from U.S. Geological Survey (2006).
Challenge Theme 6. Natural Hazard Risks in the Borderlands 193

The United States–Mexican border region has experienced several catastrophic fires in recent years. In October 2003,

wildfires burned hundreds of thousands of acres of land in the San Diego, Calif., area and spread rapidly because of dry conditions

and active Santa Ana winds. Fifteen people were killed in the fire, and costs related to property loss and other destruction totaled

about $27 million. In August 2007, devastating wildfires again ravaged southern California; they burned more than 202,000

hectares (over 500,000 acres), caused 9 deaths and 85 injuries, destroyed at least 1,500 homes, and resulted in about $1 billion 

in damage in the San Diego area (Flaccus, 2007). Wildfires have also burned national forest and grassland areas in southern

Arizona and New Mexico and along the border of northern Sonora and Chihuahua.

wildfires
After the 2007 southern California wildfires, the USGS Multi-Hazards 

Demonstration Project immediately began to assess the potential risk for 

secondary hazards of the fires, such as debris flows, increased flood risk, 

water quality degradation, and ecosystem damage affecting human health. 

Researchers collected and analyzed ash and burned soil to assess the effect 

of ash and burn products on ecosystems and water supplies. Preliminary 

geochemical analyses of selected samples (Plumlee and others, 2007; Wolf and 

others, 2008) showed some elevated concentrations of metals and alkalinity in 

ash, which could be of concern to human health. The project also conducted 

aerial surveys and collected spectral imaging data on key burn areas and 

compiled hazard maps for debris-flow warning systems (Cannon and others, 

2007). The expertise of the USGS in using integrated geochemical and remote 

sensing techniques and in collecting and analyzing LIDAR, ASTER, and Landsat1

imagery in vulnerable areas is crucial in the monitoring of wildfire effects on 

erosion, sedimentation, and ecosystems.

1 LIDAR, light detection and ranging; ASTER, the Advanced Spaceborne Thermal Emission and Reflection

Radiometer; Landsat, a satellite that collects images of earth from space. Each is a method of remotely collecting data 

on the earth’s surface from aircraft (LIDAR) or space (ASTER and Landsat).

U.S. eological Survey 

Support Activities Related to 

the 2007 Southern California 

Wildfires

G 

After the smoke has cleared, 

a U.S. Geological Survey 

geologist collects ash and soil 

samples following the 2007 

southern California wildfires.

. . . .facing the challenge
Los Angeles

San Diego

Smoke

UNITED STATES

MEXICO

CALIFORNIA

ARIZONA

BAJA CALIFORNIA

SONORA

PACIFIC OCEAN

Gulf of California

Challenge Theme 6. Natural Hazard Risks in the Borderlands 195

Satellite image of fires burning in southern California on October 24, 2007. For more information on 

this image, see http://earthobservatory.nasa.gov/NaturalHazards/view.php?id=19225. Modified from 

National Aeronautics and Space Administration (2007).
(Left) Flooding along the Rio Grande below Presidio, Texas, after 

monsoon rains in northern Mexico, 2008

(Facing page) Satellite image of Hurricane Claudette in 2003 

centered over southern Texas and northern Coahuila. For more 

information on this image, see http://earthobservatory.nasa.gov/

NaturalHazards/view.php?id=11746.

196 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Hurricanes and Floods

Hurricanes affect the Borderlands primarily in Texas and Tamaulipas along the Gulf of 

Mexico. One of the most devastating hurricanes that occurred in the Borderlands was Hurricane 

Beulah (fig. 8–6), which came ashore in the sister city area of Brownsville-Matamoros (TexasTamaulipas) in 1967 as a category 3 storm with winds at 219 kilometers (136 miles) per hour. 

As much as 69 centimeters (cm) (27 inches [in]) of rain fell in the Rio Grande watershed 

during Hurricane Beulah. Related flooding caused serious damage at Harlingen and McAllen,

Texas, and inundated thousands of acres of agricultural lands along the Rio Grande in parts of 

Tamaulipas and Texas.

floods
Challenge Theme 6. Natural Hazard Risks in the Borderlands 197

Although much of the Borderlands is desert, devastating flash floods from severe thunderstorms can occur. Major effects

of flash floods include inundation of urban infrastructure and farmland, destruction of property, contamination of water supplies,

and loss of life. Effects of flooding can also contribute to human health risks, such as bacterial contamination of water supplies

and recreational waters. The 2006 floods in the sister city area of El Paso–Ciudad Juárez (Texas-Chihuahua) were caused by a

series of heavy summer thunderstorms from July 27 through August 6 with a total rainfall of about 38 cm (15 in). Early research 

of the flooding caused by these storms indicates that accelerated urban growth in high-risk areas such as arroyos and a series of

unusually severe storms combined to produce the damage experienced in the region (C. Brown, New Mexico State University, 

written commun., 2008).

TEXAS

CHIHUAHUA

COAHULA

NUEVO LEÓN

Gulf of Mexico

UNITED STATES

MEXICO

NEW MEXICO
TEXAS

LOUISIANA MISSISSIPPI ALABAMA

NEW MEXICO

UNITED STATES

MEXICO

Hurricane Beulah

September 18–24, 1967

Maximum inches of rainfall:

Pettus, TEXAS, 27.38”

Gulf of Mexico Gulf of California 

1

3

5

7

10

15

20

25

EXPLANATION

Rainfall, in inches

198 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Figure 8–6. Total rainfall in inches for Hurricane Beulah during 

landfall on the Gulf Coast in 1967 (above), and satellite image 

of Hurricane Beulah taken by TIROS VII on August 22, 1967 (top 

right). Areas along the Texas coast experienced flooding in the 

days after the hurricane (bottom right). Data for landfall figure 

from the National Climatic Data Center and the Comisión Nacional 

del Agua [National Water Commission]; modified from National 

Oceanic and Atmospheric Administration (2012). 

hurricanes
Challenge Theme 6. Natural Hazard Risks in the Borderlands 199

August 22, 1967

September 1967
Urban development in the upper reach of an arroyo near El Paso, Texas, increases flood risks for 

residents in the lower reach.

Intense urbanization in sister city areas along the United States–Mexican 

border coupled with extreme precipitation events increase the risk and 

vulnerability of these areas to natural disasters, especially those cities in 

the lowest economic tier. The differences in urban structure between Mexican 

and United States cities—dense population areas with a proliferation of 

substandard housing in low-income areas in Mexico (Chardon, 1999; Lopez 

and others, 2001) and urban sprawl in low-density developments in the United 

States (Johnson, 2001)—provide a unique research environment to study 

differences in urban vulnerability to natural disasters. The vulnerability of 

a community to a natural hazard is a function of the risk of the hazard and 

the development patterns of the built-up environment, such as business 

enterprises, community social structure and services, and natural resources 

related to natural hazards (Wood, 2006). Therefore, the policies, regulations, 

and decisions made before, during, and after the event greatly affect the 

hazard risk.

Vulnerability and Risk Analysis 

for Sister City Areas along the 

United States–Mexican Border

. . . .facing the challenge
Challenge Theme 6. Natural Hazard Risks in the Borderlands 201

From an engineering framework, flood risk models incorporate physical environmental datasets such 

as elevation and slope, soil infiltration capacity, evapotranspiration rates, surface runoff rates based on 

land-cover types, and structural conveyance facilities. Land-use modifications to the manmade environment 

are only considered in reference to changes in surface runoff rates (impervious cover, flood drainage 

conveyances, and so on), yet they play a critical role in assessing the vulnerability of the community to a 

natural hazard such as flooding.

Geographers with the USGS have refined processes based on geographic information systems (GIS), 

such as the Community Vulnerability Assessment Tool (CVAT; Flax and others, 2002), to assess the 

intersection of hazards and community resources. Tsunami vulnerability research along the Pacific Coast 

performed by Wood and Good (2004) incorporates readily available GIS layers such as the National Land 

Cover Dataset, U.S. census population and business economic data, major infrastructure data including 

essential facilities, and tax parcel values. Applying this similar CVAT process to assess the vulnerability 

of the population for sister city areas along the United States–Mexican border can assist Mexican and 

United States land-use planners and emergency response staff in reducing potential economic losses 

from flood hazards. Additional data, such as for hazardous waste and agricultural activities, provide 

information necessary for the community to address preparedness issues such as debris removal. Using 

the CVAT process, composite maps can be created to help community stakeholders set priorities, identify 

community vulnerability “hotspots,” and discuss new zoning regulations.
202 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

 USGS Capabilities

The USGS possesses advanced capabilities for monitoring natural hazards, analyzing 

levels of risk and vulnerability for disaster prone areas, providing damage assessment data 

after extreme events, and providing timely, unbiased science information to emergency 

response officials, resource managers, and the public, helping to reduce property damage,

injury, and loss of life.

The USGS Multi-Hazards Demonstration Project (http://urbanearth.usgs.gov/) helps 

communities in southern California reduce their vulnerability to catastrophic loss from 

earthquakes, wildfires, landslides, tsunamis, and coastal erosion. Long-term project objectives

are to establish open communication between scientists and disaster managers and planners, 

plan USGS research with collaborators to further the goal of improved resiliency to natural 

hazards, initiate or expand real-time monitoring and warning systems, and provide easy access 

to new and existing hazards data, information, assessments, and models to facilitate integration 

and use by decisionmakers and researchers.

The USGS Global Seismographic Network monitors earthquake data and can relay that 

information to governments and the public during major earthquake events in real time. The 

USGS also developed PAGER, Prompt Assessment of Global Earthquakes for Response, an 

automated system that uses shaking hazard maps to rapidly estimate the number of people and 

communities exposed to severe shaking during earthquakes anywhere in the world. Federal, 

State, and local agencies also use shaking hazard maps to create and update seismic design 

provisions in building codes.

The USGS Landslides Hazards Program monitors landslides in real time and conducts 

research on precipitation-induced landslides and debris flows. The resulting information is

shared with decisionmakers and the public to assist in developing landslide mitigation and loss 

reduction strategies and predicting where and when these hazards are likely to occur.

For wildfire preparedness, the USGS collaborates with other Federal, State, and local

agencies to prepare maps of vegetation, fuels, and past burn areas. It also provides information 

to the public to identify wildfire risks, reduce fire hazards, develop emergency response plans, 

and assess wildfire damage and its aftermath.

To address major hurricane disasters, the USGS collects coastal impact data through 

remote sensing techniques to map the extent of flooding. Activation of current remote sensing

data can be implemented through the International Charter on Space and Major Disasters, of 

which the USGS is both a participating member and an authorized user. Through the member 

agencies, the International Charter provides a unified system of space data acquisition and

delivery to those affected by natural or man-made disasters.

The USGS assists in flood warning and emergency management activities by collecting

streamflow data and displaying real-time streamflow maps for use by Federal, State, and local

agencies. For the 2006 El Paso flood post-assessment, the USGS collaborated with the U.S.

Army Corps of Engineers (2007) to collect field data at arroyo channels and precipitation

monitoring sites.

References cited in this chapter are listed in chapter 12.
Challenge Theme 6. Natural Hazard Risks in the Borderlands 203
Challenge Theme 7. Information Support 

for Management of Border Security and 

Environmental Protection

By Jean W. Parcher and William R. Page

Introduction

Historically, international borders were located far from the 

major political and economic capitals of their countries and rarely 

received adequate planning or infrastructure development. Today, as a 

result of global economics and increased movement of goods between

nations, border regions play a much greater role in commerce, tourism,

and transportation. For example, Mexico is the second largest destination 

for United States exports (Woodrow Wilson Center Mexico Institute, 

2009). The rapid population and economic growth along the United 

States–Mexican border, undocumented human border crossings, and 

the unique natural diversity of resources in the Borderlands present 

challenges for border security and environmental protection. 

Assessing risks and implementing sustainable growth policies to protect 

the environment and quality of life greatly increase in complexity when 

the issues cross an international border, where social services, 

environmental regulations, lifestyles, and cultural beliefs are unique 

for each country. Shared airsheds, water and biological resources, 

national security issues, and disaster management needs require an 

integrated binational approach to assess risks and develop binational 

management strategies.

Chapter 9
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 205
206 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Border Security and Environmental Protection Issues

Both national security and environmental protection are critical issues along the border. The challenge is to integrate these 

issues and develop a plan that is beneficial and acceptable to both the United States and Mexico. Frequent consultation and joint

decisionmaking between the two countries provide for a more effective solution to security and environmental issues than would 

separate plans that do not take into account shared concerns and issues. The common objectives that are shared by the entities 

in charge of securing our border and protecting the environment include protection of critical infrastructure, development of a 

national incident management system, and use of technology 

and intelligence—all to be accomplished in ways that sustain a 

healthy environment (Schoik, 2007). 

The extensive border between the United States and 

Mexico runs through urban sister city areas, Native American 

tribal lands, national forests, U.S. Department of Defense 

properties, national parks, and other U.S. Department of Interior 

lands (see poster, figs. 2–3 to 2–6). Because these Federal

lands are in various management jurisdictions and are primarily 

rural and unpopulated, they create the opportunity for a large 

volume of illicit cross-border activity. This activity has created 

significant security challenges to our Nation in protecting and

maintaining border integrity, but authorities have responded by 

securing waterways, preventing undocumented crossings and 

subterranean tunnel activities, and apprehending illegal drug 

traffickers in both urban and rural settings.

U.S. Customs and Border Protection Air and Marine group 

conducting aerial operations with an unmanned aircraft system
Figure 9–1. Illegal immigrants 

apprehended near the border. 

Figure 9–2. Apprehended vehicle loaded with marijuana.

Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 207

Emphasis on national security along our borders greatly increased after the events of September 11, 2001. The United 

States–Mexican border has 39 ports of entry which facilitate over 300 million legal crossings a year and almost $650 million 

a day in binational commerce, including critical energy supplies (United States–México Border Health Commission, 2007; U.S. 

Customs and Border Protection, 2007; U.S. White House, 2007). Illegal crossings and the smuggling of people, drugs, cash, 

and weapons occur in both directions along the 3,141-kilometer (km) (1,952-mile [mi]) border (figs. 9–1 and 9–2) and result

in significant costs related to intelligence and enforcement, loss of life, and adverse effects on the environment. From the

mid-1990s to 2006, more than a million illegal immigrants were apprehended and deported each year. Most immigrants are 

Mexican nationals, and a small percentage of people were from Central America, South America, and Asia (Sapp, 2011). From 

1998 to 2005, migrant deaths from illegal border crossings doubled due to a shift in migration routes from urban areas to rural 

areas. In the past few years in Mexico, violence associated with Mexican drug cartels has resulted in an increase in drug, cash, 

and weapons smuggling and the deaths of thousands of people in Mexico, many in the border cities of Tijuana, Baja California, 

and Ciudad Juárez, Chihuahua—as of 2009, cartels caused 12,000 deaths in Mexico (Napolitano, 2009), and the number of 

deaths continue to grow. The violence has worsened so much that the U.S. Department of Homeland Security and its 

cooperators continue to strengthen security in order to disrupt the smuggling operations helping to fuel cartel violence in 

Mexico and prevent its spillover into the United States (U.S. Department of Homeland Security, 2011). 

(Below) Patrolling for opium 

near the United States–Mexican 

border near Tijuana, 

Baja California, 1948
eographic information systems (GIS) and the development of extensive 

geodatabases have become invaluable tools for addressing a variety of 

contemporary societal issues and making predictions about the future. The 

USGS Border Environmental Health Initiative (BEHI; http://borderhealth.

cr.usgs.gov) United States–Mexico Border Geographic Information System 

(USMX-GIS) is based on fundamental datasets that are produced and (or) 

approved by the national geography agency of each country—the U.S. 

Geological Survey (USGS) and the Instituto Nacional de Estadística y 

Geografía (INEGI) [National Institute of Statistics and Geography]—and the 

International Boundary and Water Commission. The data are available at 

various scales to allow both regional and local analysis (Parcher, 2008). The 

signing of the USGS and INEGI Project Annex Six, which provides the legal 

framework for public access to the best available harmonized binational 

geospatial datasets along the United States–Mexican border, allowed full 

public access to the numerous transboundary GIS datasets developed by 

the BEHI project. 

United States–Mexico Border 

eographic Information System

United States–Mexican border crossing at San Ysidro, San Diego, California

G 

G 

. . . .facing the challenge
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 209

The United States–Mexico Border Environmental Health Initiative (BEHI) Internet map service user interface. Dataset layers can be 

selected through the Layer Manager. (http://txpub.usgs.gov/borderhealth/) 

The USMX-GIS extends GIS development to include national level cooperation between various 

agencies in both countries to provide harmonized geospatial and thematic datasets. These binational 

harmonized datasets are available in a range of raster products: 

• high-resolution digital orthophotographs, digital elevation models, and satellite imagery;

• demographic information—population density, populated areas, transportation, geographic names, 

hospitals, schools, and international, State, and local government administration boundaries;

• water information—watersheds, hydrographic networks, and water quality data;

• physical features—geologic maps, land use, and land cover; and

• contaminants—in biota, potential sources of contaminants, and soil geochemistry.

These datasets can be viewed in an Internet map service at http://txpub.usgs gov/borderhealth/ and are 

available for public download through a file transfer protocol (FTP) Web site at http://borderhealth.cr.usgs.

gov/datalayers.html.
Underground tunnels used in illegal smuggling operations are a 

significant security challenge along the United States–Mexican border, and 

dozens of these tunnels have been documented, mainly in California and 

Arizona. Border security agencies rely on the support of USGS geophysicists 

for the advancement of technology used to detect illegal tunnels along the 

border. Scientists with geophysical expertise serve on technology assessment 

teams whose major role is to evaluate different geophysical techniques that 

can be used for tunnel detection. They collaborate with security agencies 

to conduct site characterization surveys—the collection of important 

geophysical data, including electrical measurements, helps to define subsurface 

soils and rock that can host buried tunnels. The scientists collect samples of 

tunnel rock and perform laboratory analyses to determine physical properties 

of these samples, including density, magnetic susceptibility, resistivity, and 

water content. These characteristics provide important clues in understanding 

why tunnels are constructed in certain areas and help predict the location of 

undetected tunnels in other areas along the border. Scientists then contribute 

to tunnel detection technology reports which summarize their site characterization 

and evaluation investigations.

U.S. eological Survey Support in 

Tunnel Detection Technology

G 

. . . .facing the challenge
Tunnel Entrance

MEXICO

UNTIED STATES

Tunnel Exit

(V&F Distributors

Warehouse)

Border Fence

DEA

DEA

Border Security and Environmental Protection Issues 211

A U.S. Geological Survey (USGS) scientist collects geophysical 

data along the United States–Mexican border (facing page). 

The data collected by the USGS helps border security agencies 

find smuggling tunnels near the United States–Mexican border, 

such as this tunnel under Otay Mesa in California (top left). 

These bales of marijuana (bottom right) were seized from the 

tunnel by the Drug Enforcement Administration in January 2006. 

Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 211

tunnels
Special operations training for 

U.S. Navy and U.S. Air Force 

personnel at Elephant Butte 

Reservoir, New Mexico, 1990

212 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Terrorism threats on infrastructure and on United States and Mexican citizens are also a concern in the Borderlands and 

create challenges for securing our shared binational waterways, including the Rio Grande and associated reservoirs and dams 

(Amistad and Falcon Reservoirs and Dams in Texas and Elephant Butte Reservoir and Dam in New Mexico) and the Gulf Coast 

and Pacific Coast areas. Heightened terror alerts have been posted in the past for some railways along the border; alerts may also

affect other transportation hubs including shipping ports, airports, and truck and bus depots, as well as other infrastructure such 

as chemical, military, and communication facilities and natural gas and electrical lines that cross the border region. 

Two other important security challenges are improving readiness for response to and recovery from disasters—which 

include not only terrorist attacks but also natural events such as earthquakes, wildfire, landslides, and flooding—and controlling

the spread of infectious disease such as avian influenza or the H1N1 virus. For example, the Gulf Coast areas of Tamaulipas and

southern Texas are extremely vulnerable to hurricanes and associated flooding, such as Hurricane Beulah in 1967, which caused

severe flooding and inundated thousands of acres of agricultural land in the lower Rio Grande valley (see chapter 8). Because

of a humid and temperate climate, these areas have also experienced recent outbreaks of dengue fever and are vulnerable to the 

spread of other vector-borne disease such as the West Nile virus. On the western end of the border, southern California and Baja 

California, the most heavily populated areas of the Borderlands, have experienced devastating earthquakes and wildfires in

recent years, which resulted in loss of life and millions of dollars of damage to infrastructure and property.

A drainpipe on the Mexican side of the border leaves a gap in the fence at Calexico, California, 1979
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 213

Sonoran pronghorn (Antilocapra americana sonoriensis)

Bighorn sheep (Ovis canadensis)

Trash left behind by illegal 

immigrants

Another unfortunate aspect of illegal immigration and other criminal activity for border security authorities to consider is 

the deleterious effect such activity has on the limited natural resources and fragile wildlife habitat of the Borderlands (Cordova 

and de la Parra, 2007). For example, in the Buenos Aires National Wildlife Refuge in southern Arizona, illegal immigrants have 

left behind about 500 tons of trash (fig. 9–3), have abandoned hundreds of vehicles, and have forged more than 2,092 km (1,300 mi)

of trails that traverse the land (Swarbick, 2007; Viramontes and Brown, 2008). Border security itself—in the form of border 

fences and walls constructed by the U.S. Department of Homeland Security (figs. 9–4 and 9–5)—though important to the

prevention of illegal activity, can also negatively affect Borderlands ecosystems (Flesch and others, 2010). These physical barriers 

prevent the natural migration of wildlife and may cause habitat fragmentation, eventually leading to a decline in wildlife populations 

and possible total species loss. This issue is of particular concern in the many protected lands in the Borderlands, including Big 

Bend National Park (Texas), the adjacent Reserva de la Biosfera Maderas del Carmen [biosphere reserve] and Área de Protección 

de Flora y Fauna Cañón de Santa Elena [protected flora and fauna area] in Mexico (Coahuila and Chihuahua), Organ Pipe Cactus

National Monument (Arizona), Cabeza Prieta National Wildlife Refuge (Arizona), and San Pedro Riparian National Conservation 

Area (Arizona). Many of the animals that occupy these lands are uncommon in the first place, partly because they reside at

the northern limit of their habitat. Wildlife that may be affected by the construction of border fences include the Mexican black 

bear (Ursus americanus eremicus), Mexican gray wolf (Canis lupus baileyi), ocelot (Leopardus pardalis), jaguar (Panthera onca; 

already endangered), bobcat (Lynx rufus), puma (Puma concolor), Sonoran pronghorn (Antilocapra americana sonoriensis), 

bighorn sheep (Ovis canadensis), and various reptile and amphibian species. Many border fences are planned to have bright 

lighting, which may adversely affect bats and migratory bird populations. Other problems associated with border fences include 

the buildup of sediment and trash along rivers and drainages crossing the border, which can potentially disrupt natural river 

ecozones such as wetlands and other sensitive habitats.
214 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Ferry boat crossing near 

Calexico, California, 1906

View of Calexico-Mexicali 

border crossing station from 

United States side, 1950

Vehicle inspection at the 

Calexico-Mexicali border 

crossing station, 1948

Border Crossings at Sister Cities , and

then

(Background image)

View south into 

Mexicali, Baja California, 

from Calexico, California 

Calexico, California

Mexicali, Baja California
Calexico east port of entry, 

2003

Calexico port of entry, 

2003

Vehicle inspection at the 

Calexico-Mexicali border 

crossing station, 2012

now

Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 215
TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

SONORA

3

BUENOS AIRES

NATIONAL WILDLIFE

REFUGE

216 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Figure 9–3. Trash left behind by illegal immigrants at Buenos Aires National Wildlife Refuge, Arizona. 

The U.S. Department of the Interior (DOI) manages 18 national parks, 15 wilderness areas, 3 national monuments, and 

6 recreation or conservation areas within the Borderlands (see poster, figs. 2–2 to 2–5). Additionally, there are 12 wildlife refuges

and 12 tribal entities, some of which span the border. Thus, each DOI bureau with land interests in the area—U.S. Fish and 

Wildlife Service, National Park Service, Bureau of Land Management, Bureau of Reclamation, and Bureau of Indian Affairs—

has land and resource management issues along the border that are tied directly to their bureau mission mandates. The DOI 

U.S.–Mexico Border Field Coordinating Committee (FCC; http://www.cerc.usgs.gov/fcc/) facilitates communication and 

coordination among all DOI bureaus and consultation with Mexican counterparts through biannual meetings, information sharing, 

and working groups established to address specific subjects directly related to border security, environmental protection issues

including climate change, invasive species, and water availability and quality. By assisting the member bureaus in building 

partnerships and enlisting volunteers, the FCC advances its objectives of improved communication, coordinated activity, and 

implementation of the best conservation practices in the Borderlands. Through binational cooperative efforts facilitated by the 

FCC, scientists in the United States and Mexico share long-term data and technical expertise to recognize and monitor border 

security activities and the effects of urbanization and agriculture in these preserved lands.
Border fence crossing irrigation canal Debris accumulation at a drainage grate

Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 217

Figure 9–4. Fence along the United States–Mexican border at Buenos Aires National Wildlife Refuge, Arizona. 

Figure 9–5. Newly 

constructed fence on the 

United States–Mexican border 

near the San Diego–Tijuana 

sister city area (California–

Baja California). 
 USGS Capabilities 

The expertise of the U.S. Geological Survey (USGS) in mapping, modeling, and 

integrating scientific databases, combined with long-term partnerships with Mexican Federal

agencies, provides a strong foundation to address the issues of national security and environmental

protection and management. The USGS Border Environmental Health Initiative (BEHI; 

http://borderhealth.cr.usgs.gov) recognized the need for transboundary science datasets based 

on a geographic information system (GIS) to address myriad Borderlands issues and, as a 

result, developed the United States–Mexico Border Geographic Information System, an Internet 

mapping service containing integrated binational, multidisciplinary GIS datasets, many of 

which are directly applicable to solving border security and environmental issues (Parcher, 2008).

These datasets provide a temporal baseline used to analyze information needed to facilitate 

joint planning activities related to securing the border, improving readiness for response to and 

recovery from disasters, and improving sustainable development practices related to natural 

resource conservation. Some of the BEHI datasets that support border security and environmental 

management activities include remote sensing data, geology, hydrology, geographic features 

(such as international and local boundaries), urban areas, named features, transportation and 

infrastructure, census data, and human health data.

The USGS has expert capabilities in remote sensing technology that can provide valuable 

tools for monitoring border security, observing the environment from space, and extracting 

detailed elevation data for improving readiness for natural disasters such as hurricanes and 

floods. These data are also used in regional and local planning and economic development.

The most common remote sensing datasets include Landsat imagery (facing page and fig. 9–6),

digital orthophotographs (fig. 9–7), digital elevation models (DEMs; fig. 9–8); and light detection

and ranging (LIDAR) imagery (fig. 9–9). The USGS and the International Boundary and Water

Commission (IBWC), in cooperation with the Instituto Nacional de Estadística y Geografía 

(INEGI) [National Institute of Statistics and Geography], have compiled newly revised demarcation 

maps for the international boundary based on high-resolution remote sensing datasets, including 

digital orthophotograph imagery. Remote sensing datasets are critical in identifying illegal 

roads and trail networks associated with illegal immigration and other smuggling operations 

in rural parts of the border, and satellite imagery and digital orthophotographs are essential in 

detecting illegal dump sites in the border region that can contain hazardous waste or other toxic 

materials. Remote sensing, combined with transportation datasets, is also useful in monitoring 

infrastructure potentially subject to terrorist threats, such as dams and reservoirs, bridges, 

buildings, transportation, and other features.

218 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 219

English Español
220 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Brownsville, 

TEXAS

Matamoros,

TAMAULIPAS

RIO GRANDE

RIO BRAVO

UNITED STATES

MEXICO

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

8

Figure 9–6. Landsat 7 ETM+ multispectral satellite image of the 

Brownsville-Matamoros sister city area (Texas-Tamaulipas).
El Paso, TEXAS Ciudad Juárez, CHIHUAHUA

UNITED STATES MEXICO

Santa Fe Bridge

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

4 5

Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 221

digital orthophoto

Figure 9–7. Digital orthophotograph showing the Santa Fe Bridge 

crossing from El Paso, Texas, to Ciudad Juárez, Chihuahua.
222 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

ARIZONA NEW MEXICO

SONORA

CHIHUAHUA

Douglas

Bisbee

Naco Agua Prieta

UNITED STATES

MEXICO

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

4

3

Figure 9–8. Digital elevation model of the area surrounding 

the Douglas–Agua Prieta sister city area (Arizona-Sonora). Gray 

colors indicate higher-elevation mountain ranges; tan colors 

indicate lower-elevation basins.
Brownsville, TEXAS

Matamoros, TAMAULIPAS

UNITED STATES

MEXICO

Courtesy of the University of Texas Center for Space Research

RIO GRANDE

RIO BRAVO

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

8

Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 223

light detection and ranging

Figure 9–9. High-resolution LIDAR elevation model of the 

Brownsville-Matamoros sister city area (Texas-Tamaulipas). 

Green colors indicate higher-elevation areas; brown colors 

indicate lower-elevation areas.
One of the most common applications of remote sensing techniques used by USGS 

scientists is the mapping, monitoring, and modeling of natural and human changes in the 

environment. Remote sensing, in conjunction with land use and land cover datasets, helps us 

to understand and analyze the effects of these changes on humans, ecosystems, and natural 

resources so that we may take the appropriate actions in maintaining and preserving the quality 

of life in the Borderlands. One example of the unique integrated science capabilities of the 

USGS is the application of assessments of environmental effects to the many fence construction 

projects proposed in the Borderlands. Biologists with the USGS use remote sensing and other 

data to map and monitor wildlife ranges and habitats; this research can then be used to study 

the prevention of species loss and fragmentation, which can occur when border fences break 

up habitats (see chapter 3). Scientists with the USGS also use remote sensing imagery to map 

the distribution of and changes in vegetation on which different species depend for their major 

food sources. The USGS has expertise in researching the biology and ecology of biota, applying 

and developing environmental indicators, conducting baseline biological indicators, and 

establishing long-term monitoring in the Borderlands to fully understand the environmental 

effects potentially caused by border fences and walls.

U.S. Border Patrol using 

alternative transportation—

horses (above) and all-terrain 

vehicles (below)—to patrol 

difficult terrain along the 

United States–Mexican border

U.S. Army National Guard 

soldier assisting in 

border patrol operations near 

Nogales, Arizona
Light detection and ranging (LIDAR) technology is used to collect a dense network of elevation points used to model the 

topography of the ground surface. These data are extremely useful in providing information needed to assess risk and vulnerabilities 

associated with natural disasters and to prepare readiness procedures, especially for hurricane-related flooding in the Gulf Coast

areas of Texas and Tamaulipas. For example, figure 9–9 shows LIDAR data from the Brownsville-Matamoras sister city area

(Texas-Tamaulipas). The brown end of the color scale indicates areas of lower elevation along the Rio Grande; these areas are 

more prone to storm surge flooding than the green areas of higher elevation.

The USGS is also at the forefront of researching, analyzing, and integrating geologic and geophysical data that can be 

directly applied to predicting and detecting the locations of illegal smuggling tunnels crossing beneath the United States–Mexican

border. The USGS has collaborated with security organizations—including U.S. Northern Command, the U.S. Army Corps 

of Engineers, and the U.S. Department of Homeland Security—to advise them on geophysical techniques and help them 

evaluate techniques that can be used to detect underground tunnels. Geology (rock type) can determine how easy it is to tunnel or 

excavate in a given area, so it can indicate where illegal tunnels are likely to be found. For example, the USGS geologic map of 

the Otay Mesa area in southern California (fig. 9–10; cropped from Todd, 2004) shows different rock types and illustrates their

influence on potential tunneling. The Otay Formation on the west end of the map (orange geologic unit, labeled To) consists of 

poorly consolidated sandstone and soft claystone and has high potential for tunneling. The illegal tunnel shown on page 211 was 

excavated in the Otay Formation. Additionally, Quaternary rocks (yellow and tan units, labeled Qya, Qu, Qls, Qoa, Ql, and 

Qt) and Tertiary rocks (tan units, labeled Tsd, Tf, and Tmv) are soft and unconsolidated to poorly consolidated and have high 

tunneling potential. The Santiago Peak volcanics in the central part of the map (blue unit, labeled Ksp) consist of volcanic rocks. 

Though they are mostly well consolidated (solid and hard), they also contain some units that are poorly consolidated (weak 

and soft), so these rocks overall have moderate potential for tunneling. The units on the east end of the map (pink and red units, 

labeled Kc, Kmgp, Kcm, Kjv, and Kgr) are mainly hard granitic rocks. These rocks have low tunneling potential because they 

are very hard and dense and make tunneling very difficult.

A medallion showing the 

location of the international 

border between the United 

States and Mexico
UNITED STATES

MEXICO

S a n Y i s i d r o M o u n t a i n s

J a m u l M o u n t a i n s

O t a y M e s a

Otay Valley

Lower

Otay Reservoir

117°00’

32°30’

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

1

Qoa

Qu

El Cajon quadrangle

Young alluvium (Holocene)—Sand, silt, and gravel in modern streambeds

Alluvium and colluvium, undivided (Holocene and Pleistocene)—Loose deposits 

of rock debris at base of slope

Landslide deposits (Quaternary)—Deposits of earth and rock materials that moved 

downslope as landslides

Older alluvium (Holocene and Pleistocene)—Sand, silt, and gravel in old stream 

valleys

San Diego Embayment

Lindavista Formation (Pleistocene or Pliocene)—Reddish-brown sandstone and 

mixed rocks; contains iron which gives formation characteristic color

San Diego Formation (Pliocene)—Marine sandstone and mixed rocks; sandstone is 

typically fine to medium grained

Fanglomerate (Pliocene and Miocene)—Fans of boulders that are cemented 

together

Otay Formation (Oligocene)—Sandstone and claystone; light gray and light brown; 

claystone is waxy, composed almost exclusively of clay

Poway Group

Mission Valley Formation (Eocene)—Sandstone; soft and crumbly

Western Colorado Desert

Terrace deposits (Pleistocene)—Sand, silt, and gravel of stream beds higher than 

modern streams

Peninsular Ranges Batholith

Western sequence

Cuyamaca Gabbro (Early Cretaceous)—Dark, igneous, coarse grained, hard rocks

Monzogranite of Mother Grundy Peak (Early Cretaceous)—Igneous, medium to 

very coarse grained, hard rocks

Corte Madera Monzogranite (Early Cretaceous)—Granite-like rocks

Japatul Valley Tonalite (Early Cretaceous)—Igneous, coarse grained, hard rocks

Granitoid rocks (Early Cretaceous)—Granite-like rocks

Prebatholithic and Suprabatholithic rocks

Santiago Peak Volcanics (Early Cretaceous)—Hard volcanic rocks and flows

EXPLANATION

Qls

Qya

Tsd

To

Tf

Ql

Tmv

Qt

Kmgp

Kjv

Kgr

Kc

Kcm

Ksp

0 1 2 3 4 KILOMETERS

0 1 2 3 4 MILES

Base map digital layers (roads, topographic contours, and hydrography) 

were prepared from publicly-available digital line graph (DLG) data, 

El Cajon 1:100,000 metric quadrangle

Universal Transverse Mercator projection, zone 11

226 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 227

Figure 9–10. Geologic map showing the different rock types 

of the Otay Mesa area in the California border region north of 

Baja California. The soft Otay Formation in orange (labeled To) 

and Quaternary-Tertiary rocks in yellows and tans have the 

highest potential for tunneling, the Santiago Peak volcanics in 

blue (labeled Ksp) have moderate tunneling potential, and the 

hard, dense granitic rocks in pinks and reds have low tunneling 

potential. The city of Tecate, California, is about 2 miles beyond 

the east edge of the map. This map shows a part of the southwest 

corner of the geologic map of the El Cajon 30’ x 60’ quadrangle; 

modified from Todd (2004).
228 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Two U.S. Customs and Border Protection Air unit UH-60 Blackhawk 

helicopters patrolling the airspace over rugged terrain in the 

American southwest border region
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 229
230 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Water is the most critical natural resource on earth and is the lifeblood of communities, economies, and ecosystems, especially 

in the arid to semiarid Borderlands. The expertise of the USGS in compiling, integrating, and analyzing water-related datasets 

(see chapter 4) is extremely important in addressing issues such as securing our waterways from terrorist threats and assuring 

plentiful supplies of safe drinking water for future generations. Securing our waterways and assuring water quality and quantity 

involve a full understanding of hydrologic systems. Geographers with the USGS and INEGI are collaborating to harmonize a 

binationally consistent and seamless dataset of watershed boundaries and a hydrographic network of surface-water features for the 

Borderlands (fig. 9–11). This cooperative effort would provide a consistent framework for program planning, implementation, and

reporting of the binational hydrologic systems. To help in assessing safe drinking water supplies, the USGS conducts real-time 

monitoring of about 7,500 streamgages; the data from these gages are also a critical component of an experimental flash flood

and debris flow warning system jointly operated by the USGS, the National Oceanic and Atmospheric Administration, and the 

National Weather Service. To help assure and assess water quality, the USGS, the IBWC, and the Mexican Comisión Nacional del 

Agua [National Water Commission] are building a digital warehouse database for water quality in the Borderlands.

Figure 9–11 (facing page). Pilot area for the development of 

binational watershed boundaries and a networked hydrography 

for the United States–Mexican border region. The geographic 

area is along the Arizona and Sonora borders, corresponding 

with subarea 3. The binational land use and land cover dataset 

provides the background information. 
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 231

Rio Altar

Nogales

Rio Seco

Rio Agua Prieta

Arroyo Salto del Ojo

Rio Batepito

Willcox Playa

Rio Bamori

Mimbres

Upper Santa Cruz

Upper San Pedro

San Simon

Rillito

Playas Lake

Animas Valley

Brawley Wash

Whitewater Draw

San Simon Wash

Hacienda

San Francisco

Santa Rosa Wash

Aguirre Valley

San

Bernadino

Valley Cloverdale

Rio De La Concepcion

3

4

2

SONORA

CHIHUAHUA

ARIZONA NEW MEXICO

UNITED STATES

MEXICO

0 25 50 100 MILES

0 25 50 100 KILOMETERS

75

75

112° 111° 110° 109° 108°

33°

32°

31°

30°

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

2

3 4

EXPLANATION

Subareas of the border region

2 Colorado River–Gulf of California

3 Mexican Highlands

4 San Basilio–Mimbres

Binational watershed boundary

International boundary

3

Land use/land cover

Developed

Agriculture

Forest

Shrubland

Water

Barren

Grassland/pasture

Wetlands

Land use/land cover data from U.S. Geological Survey

National Land Cover Dataset, 1992,

and Instituto Nacional de Estadística,

Geografía, e Informática Uso de Suelo, Version II
232 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
Challenge Theme 7. Information Support for Management of Border Security and Environmental Protection 233

The USGS can provide valuable resources in developing 

databases and analyzing GIS data involving human health 

issues, such as the potential spread of infectious disease, and 

in defining and understanding potential connections between

impaired environments and human health (see chapter 5).

Scientists with the USGS Border Environmental Health 

Initiative (http://borderhealth.cr.usgs.gov) and cooperating 

agencies are currently analyzing and modeling census, health 

statistics, water quality, contaminant, and other datasets to better 

understand and make predictions concerning transboundary 

human health issues.

In response to natural disasters, the USGS collaborates 

with other agencies in providing timely science information 

to emergency response officials and the public to help reduce

property damage, injury, and loss of life (see chapter 8). The 

USGS mobilizes response efforts worldwide during and after 

natural disasters, providing scientific counsel on recovery and

response, such as when USGS used remote sensing techniques 

to map the extent of flooding and collect coastal impact data

following Hurricane Katrina (Farris and others, 2007). More 

recently, the USGS Multi-Hazards Demonstration Project 

cooperated with numerous agencies to provide mapping 

expertise and data collection for the assessment of secondary 

hazards and damage caused by the 2007 southern California 

wildfires (see chapter 8, p. 194). The USGS also plays a leading

role in monitoring and posting data for major earthquakes and 

landslides in real time, to provide decisionmakers and the public 

with important information needed to develop mitigation and 

loss-reduction strategies and predict where and when these 

hazards will occur. The USGS is also developing expertise in 

disaster readiness by analyzing GIS datasets to define levels of

risk and vulnerability in disaster-prone areas (see chapter 8, 

p. 200).

References cited in this chapter are listed in chapter 12.
The Borderlands and Climate Change

By Joan Fitzpatrick, Floyd Gray, Russell Dubiel, Jeff Langman, J. Bruce Moring, 

Laura M. Norman, William R. Page, and Jean W. Parcher

Introduction

The prediction of global climate change in response to both natural 

forces and human activity is one of the defining issues of our times. 

The unprecedented observational capacity of modern earth-orbiting 

satellites coupled with the development of robust computational 

representations (models) of the Earth’s weather and climate systems 

afford us the opportunity to observe and investigate how these systems 

work now, how they have worked in the past, and how they will work 

in the future when forced in specific ways. In the most recent report 

on global climate change by the Intergovernmental Panel on Climate 

Change (IPCC; Solomon and others, 2007), analyses using multiple 

climate models support recent observations that the Earth’s climate is 

changing in response to a combination of natural and human-induced 

causes. These changes will be significant in the United States–Mexican 

border region, where the process of climate change affects all of the 

Borderlands challenge themes discussed in the preceding chapters. The 

dual possibilities of both significantly-changed climate and increasing 

variability in climate make it challenging to take full measure of the 

potential effects because the Borderlands already experience a high 

degree of interannual variability and climatological extremes. 

Chapter 10
The Borderlands and Climate Change 235

The populations of the 

Borderlands are growing quickly 

and are potentially vulnerable 

to the projected effects of both 

increased climate variability and 

overall climate change. Water 

planners have only recently 

begun to acknowledge the 

substantial risks implied by 

natural long-term climate 

variability (Cook and others, 

2004), and individual States are 

now beginning to study the 

potential effects of a changing 

climate on their infrastructure and 

economies (for example, California 

Coastal Commission, 2001; Jacob 

and others, 2007). The goal of this 

chapter is to show the importance of the 

climate change issue to the Borderlands by 

discussing elements of the climate system 

that influence the Borderlands environment 

now, discussing the anticipated changes in those 

elements, and connecting those elements and 

changes with the seven challenge themes that are the 

focus of U.S. Geological Survey (USGS) science.
236 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Climatological Setting of the Borderlands

General Setting

The climate of the Borderlands ranges from temperate to extreme and includes some of the driest and hottest parts of North 

America (fig. 10–1). The region spans approximately 20 degrees of longitude and 9 degrees of latitude, from about 25°N. to

34°N., and includes over 1,829 meters (m) (6,000 feet [ft]) of elevation change. Climatologically, the Borderlands span the

convergence of two Northern Hemisphere atmospheric circulation cells near lat 30°N. This atmospheric convergence creates a

generally dry, warm climate with clear skies and enhanced evaporation. The convergence shifts north in the summer and south in 

the winter, creating seasonal climate variability. Further variability in the region is caused by the shifting positions and strength 

of these cells relative to each other and their interaction with topography and elevation (Sheppard and others, 1999). 

Other climate phenomena, some of which are periodic (for example, the El Niño–Southern 

Oscillation cycle, the Pacific Decadal Oscillation cycle, and the North American monsoon),

also contribute to seasonal variability; for example, northeastern and tropical Pacific sea-surface

temperature anomalies have been shown to correlate with precipitation (Schubert and others, 

2004; McCabe and others, 2004). 

The seasonal distribution of precipitation in the Borderlands is determined primarily by its

proximity to moisture from both the Pacific Ocean and the Gulf of Mexico. Summer precipitation

can have its origin in moisture from the Pacific Ocean, the Gulf of Mexico, or even the Gulf

of California; winter precipitation, however, is generally derived from Pacific frontal systems

moving eastward across the region (D’Arrigo and Jacoby, 1992). Average annual precipitation 

ranges from less than 12.7 centimeters per year (cm/yr) (5 inches per year [in/yr]) in the low, 

dry areas north of the Gulf of California (subarea 2) to more than 50.8 cm/yr (20 in/yr) in the 

Gulf Coast region near Brownsville, Texas (subarea 8) (fig. 10–2, bottom). Average monthly

temperatures across the Borderlands range from midsummer daytime highs in excess of 40.6°C

(105°F) in rain-shadowed, low-elevation locations such as El Centro in the Imperial Valley of

California (-12 m [-39 ft]; subarea 1) or Yuma, Arizona (34 m [112 ft]; subarea 2), to average 

midwinter low temperatures near freezing in high-altitude locations such as Nogales, Sonora 

(1,178 m [3,865 ft]; subarea 3), or El Paso, Texas (1,158 m [3,800 ft]; subarea 5) (fig. 10–2,

top). Both temperature and precipitation patterns and timing are strongly influenced by local

topography and elevation, by proximity to moisture sources, and by the interaction of these factors 

with regional climate phenomena on the synoptic scale over seasonal, annual, and decadal 

periods, and longer.

Kemp’s Ridley sea turtle 

(Lepidochelys kempii) on 

Padre Island, Texas

Queen Isabella Causeway 

at Laguna Madre, Texas

Fence along the 

United States–Mexican 

border at Tijuana, 

Baja California
120o

36o

30o

24o

114o 108o 102o 96o 90o

San Diego, CALIFORNIA Yuma, ARIZONA

Nogales, SONORA BIG BEND

NATIONAL PARK,

TEXAS

El Paso, TEXAS

Brownsville, TEXAS

Matamoros, TAMAULIPAS

Borderlands Updated Köppen-Geiger Classification

UNITED STATES 

MEXICO

PACIFIC OCEAN

Gulf of Mexico Gulf of California

Tecate, BAJA CALIFORNIA

Csb—warm temperate/

summer dry/

warm summer

BSh—arid/

steppe/

hot arid

Csa—warm temperate/

summer dry/

hot summer

BWk—arid/

desert/

cold arid

BWh—arid/

desert/

hot arid

Cfa—warm temperate/

fully humid/

hot summer

EXPLANATION

 Köppen-Geiger Classification

BSk—arid/ Climate

 steppe/ Precipitation

 cold arid Temperature

 International boundary

BSk—arid/ 

 steppe/ 

 cold arid

The Borderlands and Climate Change 237

Figure 10–1. Updated Köppen-Geiger climate classification for 

the Borderlands, based on long-term monthly temperature and 

precipitation records. Data from Kottek and others (2006); modified 

from Peel and others (2007).
238 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Figure 10–2 (facing page). Annual mean daily average 

temperature (top) and mean total annual precipitation (bottom) 

for the conterminous United States for the period 1961–1990. 

The United States–Mexican border region includes areas with 

both the lowest mean annual precipitation in the United States 

and Mexico and highest mean annual temperatures in the 

United States. Data from the National Oceanic and Atmospheric 

Administration–National Climate Data Center; http://cdo.ncdc.

noaa.gov/cgi-bin/climaps/climaps.pl.

In general, much of the Borderlands is characterized by climate extremes and intense 

weather. Hot, dry summer days can be punctuated by short-lived, intense thunderstorms that 

produce fully half the average annual precipitation in a few days, washing out roads and bridges 

and damaging structures in flash floods. Infrequent winter storm systems on the Pacific side

that pull tropical moisture into the central Borderlands can be unexpectedly intense as well, 

dropping 7.6–12.7 cm (3–5 in) in equally short times (Tucson Weather Forecast Office, 2006).

Tropical cyclones (on the Pacific side) and hurricanes (on the Gulf side) can reach well inland

after striking coastal areas, and longer-lived, pervasive conditions such as decadal or even 

multidecadal drought with significant effects on society are not uncommon (deMenocal, 2001).
EXPLANATION

< 32.0

32.0−40.0

40.1−45.0

45.1−50.0

50.1−55.0

55.1−60.0

60.1−65.0

65.1−70.0

> 70.0

EXPLANATION

< 5.01

5.01 − 12.00

12.01 − 20.00

20.01 − 30.00

30.01 − 40.00

40.01 − 50.00

50.01 − 70.00

70.01−100.00

> 100.00

Mean Total Annual Precipitation (Inches)

1961–1990

Annual Mean Daily Average Temperature (Degrees F)

1961–1990

1

2

3 4

5

6

7

8

1

2

3 4

5

6

7

8

The Borderlands and Climate Change 239

temperature

precipitation
240 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Timing and Delivery of Moisture in the Borderlands

Peak precipitation occurs at different times in different parts of the Borderlands, depending 

on the proximity to moisture sources and seasonal movement of moisture in the area. At the 

western end of the Borderlands (subarea 1), the San Diego–Tijuana sister city area (California–

Baja California) receives most of its annual precipitation during the winter months, typically 

with 85 percent of rainfall occurring from November through March, unlike the rest of the 

Borderlands, which typically see peak precipitation between May and October. In northwestern 

Mexico (exclusive of the Baja California peninsula), southern Arizona, and southwestern New 

Mexico (subareas 2–4), peak annual precipitation occurs in midsummer in association with 

the North American monsoon (Adams and Comrie, 1997). Northern Chihuahua, southeastern 

New Mexico, and the Trans-Pecos area of Texas (subareas 5–6) also experience precipitation 

maxima during the summer, but this moisture is due primarily to intense, periodic summertime 

convective thunderstorm activity and not necessarily to moisture arriving from the south in 

association with monsoonal flow. The Borderlands east of the Trans-Pecos area (subarea 7)

experience a bimodal precipitation pattern with maxima in both spring and autumn, though 

the annual maximum in these areas typically occurs in September. At the far eastern end of 

the Borderlands, from the Brownsville-Matamoros sister city area (Texas-Tamaulipas) inland 

(subarea 8), autumn delivery of precipitation includes the contribution of late-season hurricanes 

and tropical storms, which historically have produced some of the heaviest interior rainfalls in 

Texas history (Carr, 1967). The remnants of tropical cyclones originating in the eastern Pacific

Ocean can also penetrate into the west-central Borderlands, bringing late summer precipitation 

as far inland as northern New Mexico (Corbosiero and others, 2009).
The Borderlands and Climate Change 241

0 5 10 15 20 25 30 35 40 45 50 55 60 65 

Percent of total mean annual precipitation

Figure 10–3. Percentage of yearly precipitation contributed during the warm season (mid-June through mid-October), averaged over 

the period 1958–2003. The central and eastern areas of the Borderlands are very dependent on precipitation received during this time 

of the year, most of which is attributable to the North American monsoon phenomenon. The far western Borderlands, however, receive 

most of its precipitation during the cool season. Modified from Corbosiero and others (2009).

Although peak precipitation typically occurs during summer and early autumn over most of the Borderlands (fig. 10–3),

wintertime precipitation can contribute over 50 percent of the total mean annual precipitation in some areas as well. The 

importance of wintertime precipitation should not be underestimated. Winter precipitation arrives as soaking rains that move 

through the Borderlands over several days. Because evaporation is low at this time of year, the rain recharges groundwater 

aquifer systems, especially along mountain fronts. Especially wet winters during El Niño years can provide significant recovery

to these aquifer systems (Poole, 2005) and can be heavy enough to produce wintertime streamflow and reservoir levels that

exceed those observed during summer months (Magaña and Conde, 2000).
242 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Important Contributors to Borderlands Climate

Variability in climate and seasonal activity for a given area along the border is influenced

by factors such as land elevation and proximity to moisture, as described above. It is also 

affected by the state of periodic and seasonal climate regimes. For the Borderlands, those 

influential regimes are the North American monsoon and tropical cyclones, the El Nino–Southern

Oscillation cycle, and the Pacific Decadal Oscillation cycle; they are discussed in more detail

below. Any future changes to the climate state that modify these phenomena will also potentially 

modify precipitation, temperature, and the timing and variability of seasonal weather in the 

Borderlands and thus will affect several aspects of life there. For example, variability in warmseason precipitation, influenced primarily by the North American monsoon and tropical

cyclones, will affect agriculture and ecosystems management, integrated water management, 

and human health (National Oceanic and Atmospheric Administration, 2009).

North American Monsoon and Tropical Cyclones

In the central western Borderlands (subareas 2–4), the hot, dry weather of early summer 

is relieved in July when the wind shifts from west-southwest to east-southeast, bringing 

thunderstorms generated by the North American monsoon system. The North American 

monsoon circulation pattern develops over northwestern Mexico in late May and early June 

as intensifying sunlight heats dry inland areas. The hot rising air over Mexico’s Sierra Madre 

Occidental and Central Plateau pulls moisture in laterally from the eastern Pacific Ocean,

the Gulf of Mexico, and the Gulf of California, which leads to daily thunderstorms over the 

Sierra Madre Occidental from late June through mid-July. By mid-July, this atmospheric 

flow is well established over northwest Mexico and expands into southern Arizona and

southwestern New Mexico. There, it delivers moisture in the form of intermittent, sometimes 

intense thunderstorms through mid-August, when solar heating begins to decline (National 

Oceanic and Atmospheric Administration, 2009). From late August through September, the 

monsoon season comes to an end as the monsoonal flow gradually becomes disrupted by

cooling surface temperatures and a return to southwesterly winds. 

View of the Sierra Madre 

Occidental in Hostotipaquillo, 

Jalisco, Mexico
The Borderlands and Climate Change 243
244 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Monsoonal thunderstorm activity accounts for more than half the total annual precipitation 

in most of the core monsoonal area—northern Sonora, southern Arizona, and southwestern 

New Mexico—with the largest amounts of precipitation occurring in northwestern Mexico 

(fig. 10–3) (Douglas and others, 1993; Adams and Comrie, 1997). The timing and strength of

monsoonal flow, however, vary greatly from one year to the next, and the relation of the North

American monsoon to other atmospheric circulation regimes over the eastern Pacific Ocean

and North America is not yet well understood. In addition, the localized interaction of monsoonal 

circulation with the varied topography and summertime vertical convection conditions in 

the Borderlands creates additional complexity when modeling this phenomenon (Adams and 

Comrie, 1997). As a result, research into the onset, development, and evolution of the monsoon 

is ongoing and extensive (see, for example, North American Monsoon Experiment Science 

Working Group, 2004; Vera and others, 2006).

In the eastern Borderlands (subareas 5–8), late summer precipitation comes primarily 

from Atlantic hurricanes. Recent work by Corbosiero and others (2009) has also shown that 

remnants of eastern Pacific hurricanes and cyclones can contribute significant moisture to this

area in late summer, with contributions increasing from less than 5 percent of total summer 

rainfall in New Mexico to more than 20 percent in southern California and northern Baja 

California, with individual storms accounting for as much as 95 percent in some locations.

El Niño–Southern Oscillation Cycle

The El Niño–Southern Oscillation (ENSO) cycle is a periodic climate phenomenon

originating in the equatorial Pacific Ocean. It is a significant factor in the climate variability

of the Borderlands, as well as most of North America. In the Borderlands, El Niño years 

typically correlate with increased winter precipitation and cool temperatures, while La Niña

years correlate with decreased winter/spring precipitation and variable temperatures 

(Ropelewski and Halpert, 1986; Andrade and Sellers, 1988; Cavazos and Hastenrath, 1990; 

D’Aleo, 2002; Magaña and others, 2003). In the past, El Niño events typically occurred every 

3–4 years (Barry and Chorley, 1998; Sheppard and others, 1999), but recent observations 

suggest that while El Niño and La Niña episodes prior to 1976/1977 occurred in approximately 

equal proportion, El Niño episodes since that time have occurred twice as often as La Niña 

episodes (Trenberth, 1997). The cause of this shift is not yet understood.

The ENSO cycle has been proposed as the primary interannual modulator of precipitation

in the Borderlands (Magaña and Conde, 2000). In parts of the Borderlands, winter (December–

March) precipitation in an El Niño year can exceed 180 percent of normal, leading to an 

increased incidence of winter flooding. In the summer following an El Niño winter, the shift in

climate from extremely wet to extremely dry has been observed to correlate with an increased 

incidence of wildland fires (Swetnam and Betancourt, 1998; Kitzberger and others, 2001). In

contrast, the cooler La Niña phase of the ENSO cycle is associated with a general drying over the 

southern United States during winter and spring. For example, the 1998–2002 drought coincided 

with a protracted La Niña phase that may have been reinforced by a concurrent shift of the 

Pacific Decadal Oscillation cycle (see p. 246) to its cool phase (Hoerling and Kumar, 2003).

Monsoon over El Cajon, 

California
The Borderlands and Climate Change 245

Hurricane Douglas, south 

of Baja California, July 23, 

2002. For more information 

on this image, see http://

earthobservatory.nasa.

gov/NaturalHazards/view.

php?id=9989.
246 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Pacific Decadal Oscillation Cycle

The Pacific Decadal Oscillation (PDO) cycle is another Pacific-based quasi-periodic

climate phenomenon that has a demonstrable influence over climate in the Borderlands. With

a period lasting 20–30 years, the PDO cycle has been described as a long-lived ENSO-like 

pattern of Pacific sea-surface temperature variability (Zhang, and others, 1997), but the focus

of the effects on sea-surface temperatures is in the North Pacific Ocean rather than in the

tropical region. 

Climate conditions associated with the PDO cycle are broadly similar to conditions 

associated with the ENSO cycle. During the positive index or warm phase of the PDO cycle, 

sea-surface temperatures are warmer than average in the Pacific Ocean near the North American

coast and are contrastingly cooler than average in the central North Pacific Ocean. The current

PDO phase, which began in 1977, correlates with enhanced winter precipitation over the 

southwestern United States and northwestern Mexico, similar to the effects of the El Niño 

phase. The negative or cool phase of the PDO cycle has the opposite distribution and correlates 

with effects similar to La Niña conditions. 

The relation between ENSO and PDO is a matter of ongoing research (for example, 

whether the PDO cycle is independent of the ENSO cycle or a response to it; see Shakun and 

Shaman, 2009), but it has been noted that PDO phases can influence the effects of coinciding

ENSO phases. Some studies indicate that the timing of relative phases of the long-cycle PDO 

and the short-cycle ENSO are important in determining the overall intensity of El Niño and 

La Niña conditions (Gershunov and others, 1999; McCabe and Dettinger, 1999) and that some 

of the historically wettest and driest conditions in parts of the Borderlands have developed 

during periods when the related phases of the two phenomena coincided (Liles, 2002). Thus, 

El Niño phases of ENSO can be enhanced during the warm phase of PDO and La Niña phases 

can be enhanced during the cool phase of PDO. 

At this time, the underlying cause of the PDO cycle is not well understood and it is not 

yet possible to predict its behavior with any confidence since its long cycle time has provided

observational records over only a few cycles. Some recent observations suggest that the PDO 

phase changed from warm to cool (enhancing La Niña) with the end of the 1997/1998 El Niño 

episode (Greene, 2002; Peterson and Schwing, 2003). Other observations suggest that because 

recent anomalies in sea level and sea-surface temperature in the North Pacific Ocean do not

fit the PDO concept, consideration of this single indicator alone yields an incomplete

characterization of North Pacific climate (Bond and others, 2003).

PACIFIC OCEAN
The Borderlands and Climate Change 247

Projections for Climate Change 

in the Borderlands

Observed Current Trends

Since the late 1970s, the western United States has 

experienced climatological changes that, based on climate 

models, are unlikely the result of natural climate variability 

alone (for example, Barnett and others, 2008; Das and 

others, 2009):

• a 1°C and 2°C (1.8°F and 3.6°F) increase in mean

annual temperatures at lower and higher elevations, 

respectively (Diaz and Eischeid, 2007); 

• an increase in the elevation at which it rains rather than 

snows (Knowles and others, 2006); 

• a reduction in snowpack (Mote and others, 2005) and an 

advance in the onset of snowmelt and snowmelt-driven 

streamflow (Stewart and others, 2005);

• an advance of 8–10 days in the onset of spring 

averaged over the West (Cayan and others, 2001) 

and an associated increase in the frequency of large 

fires (Westerling and others, 2006); and

• an increase in tree mortality that may have resulted 

from pine or bark beetle (Dendroctonus spp.) infestations 

associated with longer and hotter growing seasons 

during a severe drought (Breshears and others, 2005; 

Raffa and others, 2008). 

Some additional effects suggested by climate models 

(discussed on the following pages) include increased incidence 

of droughts, floods, and heat waves.

Mountain pine beetle 

(Dendroctonus ponderosae )
248 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Global Ensemble Projections and Regional Effects

Projections from ensemble climate model simulations, reported on by the IPCC (Solomon 

and others, 2007), indicate that it is “very likely”1 North America will warm more than the 

global mean during the 21st century. Temperatures are projected to increase in the southwestern 

United States and northern Mexico by 3–4°C (5.4–7.2°F) by the end of the century (fig. 10–4,

top row). Similar projections for precipitation indicate a general drying most significant in the

winter and an overall drop in precipitation below the 1980–1999 average by as much as 30 percent 

(fig. 10–4, middle row).

Multiple global circulation model (GCM) studies are in fundamental agreement that a 

primary result of global warming will be an expansion of tropical atmospheric circulation and 

a northward shift of mid-latitude stormtracks (for example, Kushner and others, 2001; Yin, 

2005; Frierson and others, 2007; Lu and others, 2007). This expansion and shift may already 

be in progress (Fu and others, 2006), and it has been identified as a significant contributor to

southwestern drought (Seager and others, 2007). Other studies indicate that this shift should 

be accompanied by a decrease in the number of cyclones (low pressure systems) and an 

increase in their intensity (for example, Lambert, 1995; Fyfe, 2003). McCabe and others (2001) 

conclude that this decreased incidence and intensification of low-pressure systems is already

observable during in the latter half of the 20th century.

Model results also indicate that it is a decrease in wintertime precipitation (fig. 10–4,

middle row) that will be the primary cause of a transition to a sustained drier climate in the 

Southwest (Seager and others, 2007). A decrease in winter precipitation has significant

implications for future groundwater supplies in the Borderlands because many of its aquifers 

are recharged through winter precipitation. Models of the change in mean annual precipitation 

minus evaporation (P-E) reach values of 0.1 millimeter (mm) per day (0.0039 in/day) by the 

middle of the 21st century; for comparison, the 1930s Dust Bowl measured 0.09 mm/day 

(0.0035 in/day), and the 1950s drought in the Southwest measured 0.13 mm/day (0.0051 in/day). 

A quarter of GCMs indicate that P-E drying, and thus decreases in winter precipitation, may 

already be in progress.

1

 For an explanation of IPCC uncertainty vocabulary, refer to “Treatment of Uncertainties in the Working Group I 

Assessment,” Box TS.1 of Solomon and others (2007, p. 22).

Ranch manager near 

Paso Robles, California, 

inspects drought-parched 

soil, 1976

Farmer and sons walking through a dust storm in Cimarron County, 

Oklahoma, 1936
Figure 10–4. Projected changes in temperature (top row) and precipitation (middle row) over North America, from the average of the 

period 1980–1999 to the average of the period 2080–2099. Changes shown are for annual mean, mean for December–February (winter), 

and mean for June–August (summer). Note the projected changes in summer temperature (upper right) and winter precipitation (lower 

middle). Modified from Solomon and others (2007, fig. 11.12); data from the MMD-A1B simulations, averaged over 21 models.

The Borderlands and Climate Change 249

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

180° 160° 140° 120° 100° 80° 60° 40° 20°

80°

70°

60°

50°

40°

30°

20°

10°

10.0

 7.0

 5.0

 4.0

 3.5

 3.0

 2.5

 2.0

 1.5

 1.0

 0.5

 0.0

 -0.5

 -1.0

50

30

20

15

10

 5

 0

 -5

 -10

 -15

 -20

 -30

 -50

21

19–20

17–18

14–16

8–13

5 – 7

3 –4

 1 – 2

 0

EXPLANATION

Temperature response ( ̊C)

Precipitation response (%)

Number of models > 0

Annual December–January–February June–July–August

The anticipated northward shift in mid-latitude stormtracks may also be responsible for changes in early spring precipitation 

patterns. A study by McAfee and Russell (2008) indicates that such a northward shift would result in an earlier annual onset 

of warm-season atmospheric circulation patterns. The early arrival of spring weather would have potentially strong effects on 

hydrological and biological systems in the region. This effect could already be in progress; it has been observed over much of 

the western United States since the late 1970s (Cayan and others, 2001).

Taken together, these projections point to the potential for a “new normal” condition of Borderlands climate, which includes 

an increase in overall climate variability, overall intensification of the hydrological cycle, increase in aridity primarily due to

wintertime moisture deficit, increase in precipitation variability with a likelihood of fewer but more intense frontal storms, early

onset of springtime conditions, decrease in snowpack, and increase in summertime mean temperatures. In addition to these baseline 

projections, the behaviors of the North American monsoon, the ENSO cycle, and the PDO cycle must also be considered, but 

projections for their fates in a changing climate scenario remain unclear at this time. 
250 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Mesoscale Climate Projections

At 15-kilometer (km) (9.3-mile [mi]) resolution, GCMs are primarily useful for global 

and hemispheric scales, capturing interactions between ocean, atmosphere, and idealized 

landmasses. While GCM results set the overall global context for climate change, regional 

climate models (RCMs) on the mesoscale show the interaction of landscapes with climate 

processes at a more localized scale (5–10 km [3.1–6.2 mi]). The mesoscale in the Borderlands 

is detailed to the level of deserts, mountain ranges, and coastal plains and uplands, so models

on this scale will be the most informative and will support effective regional planning (Christensen 

and others, 2007).

Regional climate modeling is an emerging research area, so there are a variety of approaches 

to predict the future of climate at the scale of the Borderlands. Different approaches sometimes 

produce different results, and there may be circumstances in which the application of one 

particular approach yields more robust results than others. Though much has been written on 

model validation for regional climate modeling, there is little focus on mesoscale projections 

for the Borderlands. Some programs make their mesoscale model data available on the Internet, 

but research that applies this information to the Borderlands has only recently begun to appear 

in the literature. 

The use of ensemble modeling to help provide level-of-confidence evaluation for a regional

climate model is not yet a mature practice; at the time of this writing only a few regional studies 

use this approach (see Rinke and others, 2006; Sanchez-Gomez and others, 2009). For example, 

Hoerling and others (2009) recently attempted to reconcile the results of several publications on 

the effect of global warming on modeled runoff in the Colorado River basin (Christensen and 

others, 2004; Milly and others, 2005; Hoerling and Eischeid, 2007). The different approaches 

taken in each of the studies yielded a wide range of results—a reduction in flow from 5 to 45

percent by 2050—but they all show a similar sensitivity of streamflow to changes in precipitation—

a 2:1 ratio of percent change in flow to percent change in precipitation.

For more information on 

mesoscale model data 

available through the Internet,

see the North American 

Regional Climate Change 

Assessment Program 

(http://www.narccap.ucar.edu/).

Sensitivity studies for the 

Colorado River basin are 

important to the western 

Borderlands because the river 

supplies most of the area’s 

water supply. Future warming 

could lead to a decreased 

supply. For more information,

see McCabe and Wolock (2007) 

and Barnett and Pierce (2009). 
The Borderlands and Climate Change 251

Recent ensemble model results for precipitation change under IPCC low and high greenhouse gas emissions scenarios 

downscaled to the western Borderlands indicate the potential for a reduction in precipitation greater than 12 percent (relative 

to 1961–1990); it would begin in southern California and northern Baja California and move east by the middle of the century 

(Cavazos, 2009). Other studies that focus on potential changes in the distribution of plants and animals in Mexico project 

significant species turnover and disruptions in the ecology (for example, Villers-Ruiz and Trejo-Vazquez, 1998; Peterson

and others, 2002).
252 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Previous chapters in this report have identified the challenges of the Borderlands in the 

areas of ecology, water resources, the environment and human health, human activity, energy 

and mineral resources, natural hazards, and border security. The present climate and the 

projected changes discussed thus far will potentially affect elements of each of these challenge 

themes. Some of the most significant potential effects of climate change are discussed on the 

following pages.

Challenge Theme 1—Ecological Resources

Climate change in the Borderlands will have profound influences on the biota of the 

region, both spatially and temporally. Rates of aridification are predicted to increase, desert 

temperatures are predicted to rise as much as 3–4°C (5.4–7.2°F) (Solomon and others, 2007), 

and desert rainfall is predicted to decrease as much as 10–20 percent by 2071–2100 (United 

Nations Environmental Programme, 2007). The Sonoran and Chihuahuan Deserts have the 

highest richness of plant species of any desert region on Earth, and desert biota is adapted to 

extreme fluctuations in daily temperature and seasonal rainfall, but some species may not be 

able to adapt to such extreme rates of change.

In addition to overall trends, long-term or short-term climate variability can cause shifts in 

the structure, composition, and functioning of ecosystems, particularly in the fragile boundaries 

of the semiarid regions. The plants, insects, and animals of the Borderlands are highly specialized 

and adapted to the landscape, but a changing climate of wetter, warmer winters and overall 

temperature increases will alter their range, type, and number throughout the Southwest. For the 

Sonoran Desert, this trajectory of climate change may lead to contraction of the desert boundary 

in the southeast and expansion in the north (Weiss and Overpeck, 2005). A trend of warmer 

winters and springs and fewer instances of freezing temperatures could change the distribution 

of plant species and consequently the boundaries and overall size of the Sonoran Desert.

The health of an ecosystem is a function of many factors—water availability, temperature, 

carbon dioxide, etc.—so it is difficult to determine accurately the extent, type, and magnitude 

of ecosystem change under future climate scenarios without more highly resolved regional 

modeling efforts. Further, because the various components of ecosystems respond differently to 

shifts in climate, the overall tenuous balance among them can also change. For example, should 

vegetation cover and the moisture-exchanging properties of the land change, important local 

and regional climate characteristics such as albedo (reflectivity of the land), humidity, wind, 

and temperature will also change. Rangeland ecosystems support ranching and provide crucial 

habitat for wildlife in the Borderlands, and they comprise the largest area of grazing and ranching 

land in both Arizona and New Mexico, but the health and maintenance of these rangelands are 

climate dependent. Because changes in climate can affect the vitality and productivity of plants 

within this ecosystem, changes in climate can affect the overall success of both wildlife and 

ranching in the region.

climate and the borderlands challenge themes
The Borderlands and Climate Change 253

Increased levels of carbon dioxide (CO2) and warming temperatures can accelerate invasions 

by nonnative, flammable grasses that are currently the biggest threat to desert ecosystems.

Enrichment of CO2 will favor increased spread and productivity of red brome (Bromus rubens) 

and other winter annuals unless climate change decreases winter precipitation in the region. 

After a particularly wet winter in 2005, these annual grasses fueled extensive fires in the 

Sonoran Desert (approx. 250,000 acres [101,175 hectares] in the Cave Creek fire north of 

Phoenix) and the Mojave Desert (approx. 750,000 acres [303,525 hectares] east of Las Vegas). 

Warmer winters will push African buffelgrass (Pennisetum ciliare or Cenchrus ciliaris), which 

is sensitive to frost, upslope and to the north. Buffelgrass was planted to feed cattle in Texas 

and Sonora and to control erosion in southern Arizona, but it now threatens to become a major 

fire and ecological risk along the border from southern Texas to southern Arizona.

Climate itself can also contribute to wildfire risk. Historically, wildfires have played an 

important role in the vitality of the forest ecosystem, but the amount of land area burned per 

year by wildfires has steadily increased since the 1960s. Because of fire suppression measures 

used by management agencies, fuel loads waiting to burn have increased over time. Alternating 

wet and dry conditions over seasonal time scales or longer encourage vegetation growth—this 

biomass subsequently dries, and additional fuel reserves are created. The projected warming in 

the Southwest and sequences of wet and dry periods optimal for fuel production will increase 

fire hazard potential. This process already occurs when wet El Niño phases are followed by dry 

La Niña phases (Swetnam and Betancourt, 1998; Kitzberger and others, 2001).
254 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 2—Water Availability and Quality 

From California to Texas, the dominant climate along the border is semiarid to arid and is 

characterized by low precipitation, low groundwater recharge, and frequent drought conditions. 

The general inadequacy of the water supply has been and likely will continue to be stressed by 

projected increases in aridity, and the current demands on hydrologic resources will intensify 

with population increases and the predicted increase in drought conditions and alteration of 

precipitation patterns (Solomon and others, 2007). The strains on the supply would be felt by 

agriculture, industry, and municipalities. Studies of the effects of climate change in the southwestern 

United States have concluded that regional drying will occur as global temperature increases 

(Seager and others, 2007), and it is predicted that rainfall will be more variable with increased 

frequency of both large precipitation events and longer droughts. Increased evapotranspiration 

will occur with rising temperatures and will further strain surface-water resources. For example, 

with increased evapotranspiration and a decline in surface-water flow, irrigated agriculture will

become increasingly dependent on groundwater that is already being mined in many areas to 

supply growing urban populations. The probable outcomes of all of these predicted changes 

will be less aquifer recharge, decreased baseflow in streams, more catastrophic flooding, and

greater erosion (Lenart and others, 2004; Serrat-Capdevila and others, 2007). 

Because a substantial part of the water used in the Borderlands is derived from snowmelt 

runoff from the Sierra Nevada and the Rocky Mountains, the alteration of climate in these 

areas will also affect the hydrologic resources of the Borderlands. Snowmelt runoff from the 

Rocky Mountains produces substantial flows in the Colorado River and the Rio Grande, which

in turn provide recharge to adjacent aquifers. Increased temperatures will influence the mix

of rain and snow, the persistence of the snowpack, and the timing of snowmelt runoff, which 

already has begun to arrive earlier than historical norms (Cayan and others, 2001; Stewart and 

others, 2005). These changes in snowmelt runoff mean potentially larger winter floods but less

runoff captured in reservoirs in the Sierra Nevada and Rocky Mountains. Further, the increased 

temperatures could also result in decreased recharge, especially in areas where snowmelt is the 

dominant source of recharge (Dettinger and Earman, 2007).

The Rio Grande in 

August 2012 near 

Los Lunas, New Mexico, 

south of Albuquerque. 

Prolonged drought and 

irrigation demands 

upstream have left 

the riverbed here 

dry and the riparian 

vegetation stressed.
The Borderlands and Climate Change 255

An example of the effects of drought on water resources—Lake Mead, Nevada, in July 1983 (top) 

and July 2009 (bottom)

now

then

Previous changes in climate 

and the drying up of water 

resources have caused 

population shifts and dwelling 

abandonment in the past. For 

more information, see Polyak 

and Asmerom (2001).
256 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 3—Environment and Human Health

According to future climate scenarios, climate change could amplify human health issues 

driven by climate, such as disease transmission, air and water quality, and heat-induced illnesses 

(Gamble, 2008). Many communities are capable of preparing and adapting to these changes 

and thus minimizing human suffering, but the economically and socially disadvantaged 

populations found disproportionally along the United States–Mexican border are more vulnerable 

to the predicted negative effects of climate change (Liverman and Merideth, 2002).

Diseases such as Valley Fever, hantavirus pulmonary syndrome (Eisen and others, 2007), 

West Nile virus (Kilpatrick and others, 2008), and dengue fever are predicted to be more 

common in the Borderlands as temperature increases and seasonal and interannual patterns of 

rainfall change. Human disease issues may also be influenced by changes in animal migratory

patterns, invasions of new species, and stress-induced development of diseases in wild and 

domesticated animals.

Water quality can be expected to deteriorate as drought conditions concentrate waterborne 

contaminants and nutrients. Increased eutrophication and temperatures may also result in the 

expansion of blooms of harmful, often toxic, algae. The severity of flooding is predicted to

increase, furthering the already extant health risks of seasonal extreme flooding along much of

the border, where infrastructure is inadequate to control storm runoff and prevent the mingling 

of wastewaters with potable sources (Liverman and Merideth, 2002).

Poor air quality is also a major health concern along the United States–Mexican border, 

largely a result of emissions from idling trucks at border crossings (Good Neighbor 

Environmental Board, 2006) and airborne particulate matter, or dust (U.S. Environmental 

Protection Agency, 2009). In addition to organic contaminants released by the combustion of 

fossil fuels, dust can also diminish air quality and affect health. Health risks from dust include 

the inhalation of very small particles—particulate matter less than 10 micrometers in diameter 

(PM10) can penetrate into deep lung tissue—of mineral dust, pathogens (such as the fungal 

spores that cause Valley Fever), allergens, and toxic heavy metals and metalloids (such as lead 

and arsenic, respectively). Dust concentration, frequency of emission, and dust composition 

can all cause health problems and are susceptible to changing climate and human disturbances 

(some of which are responses to changing climate). Drying soil caused by changes in climatic 

conditions leads to greater emission of mineral dust from desert landscapes (Brazel and Nickling,

1987; Urban and others, 2009). The drying of lakes and wetlands by natural processes or human 

activities (water diversion and groundwater extraction) commonly leads to soil salinization, 

which can release salt dusts enriched in toxic metals (Gill and others, 2002; Breit and others, 

2009). Satellite images commonly capture enormous dust plumes from saline settings in northern 

Chihuahua extending into southern New Mexico and Texas and beyond (fig. 10–5). These

saline settings make up one of the largest dust sources in North America. Incidence of Valley 

Fever has been related primarily to winter precipitation and temperature that preceded infection 

by a year or more (Kolivras and Comrie, 2003). Because warm and dry conditions influence

dust emission, increasing temperatures and decreasing precipitation of the Borderlands will 

increase dust emissions and as a result will increase associated health risks. 
The Borderlands and Climate Change 257

Colony of harmful algae 

Gloeotrichia echirulata

Dust storm in Phoenix, Arizona

Drying soil can occur under 

several conditions over 

several time periods—a 

drought of a few seasons to 

a few years, the cool phase 

of the PDO cycle over a few 

decades, or widespread and 

long-term drying due to 

increasing temperatures. 

For more information on 

climatic causes of drying soil, 

see Seager and others (2007).
258 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Figure 10–5 (facing page). Satellite image of a dust storm 

carrying particulates from northern Chihuahua into southeastern 

New Mexico and the Trans-Pecos area of Texas (right). In the 

background, a dust storm moves through Lubbock, Texas, north 

of subarea 6. Increased incidence of dust events such as these 

has the potential to increase health risks from pathogens and 

environmental contaminants on both sides of the border.
COAHUILA

CHIHUAHUA

SONORA

UNITED STATES

MEXICO

TEXAS

NEW MEXICO

ARIZONA

TEXAS

CALIFORNIA

ARIZONA NEW MEXICO

CHIHUAHUA

COAHUILA

TAMAULIPAS NUEVO

LEÓN

BAJA

CALIFORNIA

SONORA Gulf of Mexico

Gulf of California

PACIFIC OCEAN

3 4

5

6

The Borderlands and Climate Change 259
Abandoned United Verde Mine 

and Little Daisy Hotel dormitory 

for miners, Jerome, Arizona

260 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 4—People in the Borderlands

Especially along the United States–Mexican border, there is a strong relation between 

human activities and environmental stressors in which both aspects perform in a reactionary 

circle. Issues that function in this circle include policy actions, human population and urban 

growth, land-use change, environmental justice, ecosystem services, sustainable development, 

cultural resources, and environmental health, which includes health risks to border families 

such as exposure to air pollution, dust, drinking water contaminants, pesticides, and other toxic 

chemicals. Climate change model projections have indicated that areas of the southwestern 

United States and northern Mexico are the most persistently susceptible to change (Seager and 

others, 2007; Diffenbaugh and others, 2008). 

According to Seager and others (2007), climate changes caused by human action will 

affect hydroclimate in the arid regions of southwestern North America and will have implications 

for the allocation of water resources and regional development. Decisionmakers and water 

resource managers must cooperate to assess their shared resources and understand how 

management of these resources will affect the health of humans and ecosystems. Extant factors 

to consider include urban development, background contamination from mineral deposits, 

irrigation, and sewage effluent, but global climate change can also combine with these issues

to potentially alter the stability of the fragile systems in the Borderlands (Seager and others, 

2007; Diffenbaugh and others, 2008; Norman and others, 2008, 2009). The direct and indirect 

effects of implementing policy not only can lead to unforeseen changes in agricultural, municipal, 

and industrial demand for water, but also could increase climate vulnerability (Norman and 

others, 2010). It is necessary to understand these interactions in order to assess how projected 

climate changes will affect a given watershed.
Urban sprawl of San Diego, California

The Borderlands and Climate Change 261
262 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 5—Energy and Mineral Resources

Mining in the Borderlands, whether for minerals (copper) or energy (coal), is a net consumer 

of water and energy resources. Mining processes cannot proceed efficiently when low rainfall

produces too little water, and either water shortages or influxes of water in excess of storage

capacity can lead to process interruptions and additional costs. Both increased aridification

and precipitation variability are increasingly likely with the projected temperature increase 

and the related intensification of the hydrological cycle, so it follows that economic stresses on

Borderlands mining operations could also increase. An increase in threatened and endangered 

species could also affect the minerals and energy sectors; as habitats are lost to change climate, 

land once leased for mining could become environmentally protected (see Bureau of Land 

Management, 2009). Given the water needs of mining operations, decreasing water resources 

could lead to public pressure to terminate mining leases on public lands in order to lessen the 

competition for already limited resources (for example, Michaels, 2001). 

Mining in the Borderlands has also left a legacy of waste rock and mine tailings that contain 

toxic metals such as arsenic, lead, and cadmium. These mine tailings, which are barren or have 

minimal stabilizing vegetation, are vulnerable to wind and water erosion. Intensification of the

hydrologic cycle associated with climate change may result in increased transport of these metals 

over significant distances to ecosystems previously too far away to be affected.

Projected changes in storm intensity and sea level can affect the ability of traditional 

energy sources to meet demands. Encroaching sea level and intensified storm surge activity

directly threaten coastal oil and gas well pads and pipelines and, through potential saline and 

fresh groundwater flooding, indirectly threaten subsurface oil and gas reservoirs. In addition,

the critical infrastructure for petroleum refineries for gasoline will become increasingly prone

to damage from intensified cyclonic activity, as was the case when Hurricane Katrina disrupted

the economy of not just the Texas coast but the entire country.

Despite the negative effects of predicted climate change on the energy sector, it may 

provide new economic benefits in energy resource development for parts of the Borderlands.

In the search for renewable energy resources that do not emit CO2, people are focusing on the 

Borderlands as a potential source for solar- and wind-based energy (fig. 10–6) (Western

Governors’ Association, 2009). Areas with a high percentage of clear-sky days (more than 

90 percent in some locations) or a class 3 wind zone categorization (average annual wind speed 

of 5.1–5.6 meters per second [m/s] [16.7–18.4 ft/s]) and the potential for large-scale utility 

development (1,500 megawatts or more) of renewable energy facilities and transmission 

infrastructure make the Borderlands ideal for the generation of solar and wind energy.

Most of the alternatives proposed to alleviate greenhouse gas emissions—solar power, 

wind turbine arrays, and electric cars—will create a significant increase in the demand for copper.

Domestic supplies of copper are largely produced in the Borderlands, primarily in Arizona 

and Sonora. Climate change may also lead to a return to preexisting and established extractive 

energy sources such as coal, oil, and gas for heating and electric power generation and for 

gasoline and diesel transportation needs. Exploitation of preexisting infrastructure for the 

exploration, production, and supply of hydrocarbon resources for fuel has an economic 

advantage over developing new nonrenewable energy sources in the short term.
CALIFORNIA

ARIZONA NEW MEXICO

TEXAS

BAJA CALIFORNIA

SONORA CHIHUAHUA

PACIFIC OCEAN

Gulf of California 

UNITED STATES 

MEXICO

0 60 120 180 240 KILOMETERS

0 60 120 180 240 MILES

EXPLANATION

Wind resource

(NREL wind power class at

50 m above ground)

3

4

5

6

7

Solar thermal resource

(DNI, kWh/m2

/day)

6.50–6.75

6.75–7.00

7.00–7.25

7.25–7.50

7.50+

QRA hub size guide

(TWh/yr)

30–35

20–25

10–15

1

25–30

15–20

5–10 – 5

International boundary

The Borderlands and Climate Change 263

Figure 10–6. Potential areas for renewable energy development (solar and wind) in the western 

United States–Mexican border region as identified by the Western Governors’ Association in 

collaboration with the U.S. Department of Energy. Data from Western Governors’ Association 

(2009). [NREL, National Renewable Energy Laboratory; DNI, direct normal insulation; QRA, qualified 

resource area; m, meter; kWh/m2

/day, kilowatthour per square meter per day; TWh/yr, terawatthour 

(1,000 gigawatthours) per year].
264 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 6—Natural Hazards

Increased incidence of drought—the single most imminent climate-related threat to the 

Borderlands—will have far-reaching adverse effects on agriculture, water availability and 

quality, energy production, and health. Droughts occurring over the last 110 years have 

challenged existing populations, yet the longer term history of most of the Borderlands indicates 

past occurrences of even more extensive droughts than those occurring in this recent past 

(Woodhouse and Overpeck, 1998). Model projections indicate that the cause of increasingly 

dry conditions will be fundamentally different from those seen in the instrumental record. 

Severe multiyear droughts over the western United States during both the recent and long-term 

past have been attributed, via GCM studies, to variations in sea-surface temperatures in the 

tropical Pacific Ocean, but future (and possibly current) aridification is attributed to increasing

moisture divergence and changes in atmospheric circulation cells that include overall expansion 

of subtropical dry zones (Seager and others, 2007). Thus, the periodic occurrence of dry 

conditions associated with the La Niña phase of the ENSO cycle will be superimposed on an 

increasingly dry base state.

Despite increasing aridification over much of the Borderlands, seasonal episodic flooding

is predicted to increase primarily as a consequence of increased intensity of precipitation events 

and decreased natural flood-buffering capacity (Karl and others, 2009). Events such as the

devastating floods of 2006 in the El Paso–Ciudad Juárez sister city area (Texas-Chihuahua) and

southern Arizona (see chapter 8) are likely to become more frequent.

Since the 1960s, the amount of land burned by wildfires each year in the United States

has steadily increased in part because of increasing fuel accumulation resulting from fire

suppression practices. As previously discussed, increasing aridification and alternating wet and

dry conditions over longer time periods in the Borderlands will increase the availability of fuel 

and enhance wildfire risk (Swetnam and Betancourt, 1998; Brown and others, 2004). Increased

incidence of wildfire poses a compounded threat because burned areas are highly vulnerable to

potential flooding, landslides, debris flows, and rapid erosion due to vegetation loss (Kirkham

and others, 2000; Cannon, 2001).

Sea-level rise is a heretofore unfamiliar hazard in the Borderlands. There is strong 

evidence that global sea level is currently rising at an increased rate after a 1,900-year period 

of little change. During the 20th century, globally-averaged sea level rose at a rate of about 

1.7 mm/yr (0.067 in/yr), and it has risen at a rate of about 3 mm/yr (0.118 in/yr) since 1993 

(Bindoff and others, 2007), but it is not a globally uniform phenomenon. Coastal areas of the 

Borderlands, especially the Gulf Coast and the Colorado River delta, will be vulnerable to the 

consequences of rising sea level in a warming world (Martinez-Gutierrez and others, 2008; 

Weiss and Overpeck, 2009). Increasing global temperatures cause sea-level rise through the 

thermal expansion of warming ocean water and melting of land-based glacier ice (Bindoff and 

others, 2007); modest IPCC projections predict a sea-level rise of 0.21–0.48 m (0.69–1.57 ft) 

by the end of the century, but these are acknowledged to be unrealistically low estimates.

Hazards associated with sea-level rise are not confined to the immediate threat of periodic

inundation—they also include increased coastal erosion, enhanced storm surges in association 

with cyclonic activity, and saltwater incursion of coastal aquifers. Potential outcomes of these 

hazards will be strongest on the Gulf Coast segment of the Borderlands, where sensitive 

ecosystems associated with Padre Island and Laguna Madre are at risk, as are infrastructures 

associated with the Gulf Intracoastal Waterway and oil refining activities. In the Gulf of

California, the primary risk associated with rising sea level is the migration and loss of habitat 

for the area’s diverse flora and fauna, especially in the Colorado River delta environs.
The Borderlands and Climate Change 265
266 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Challenge Theme 7—Border Security and Environmental Protection

Climate change does not respect borders, nor are the effects of climate change distributed 

equally. Population growth and intensified water demand related to socioeconomic changes and

climate uncertainties such as droughts and floods greatly increase the vulnerability of populations

on both sides of the border. For the Borderlands, monitoring environmental and socioeconomic 

effects of climate change, mitigating the consequences, and responding to extreme weather 

events require open sharing of environmental, demographic, and economic data to allow 

decisionmakers to develop short- and long-term strategies. Differences in economic development 

between the United States and Mexico, coupled with the projected increase in the risk and 

vulnerability of populations at the lower end of the economic scale, have the potential to 

increase migration of climate affected refugees into the United States.

Satellite image of 

El Paso, Texas (top), 

and Ciudad Juárez, 

Chihuahua (bottom). 

For more information on 

this image, see http://

earthobservatory.nasa.gov/

IOTD/view.php?id=4206.

El Paso, TEXAS

Ciudad Juárez, CHIHUAHUA

UNITED STATES

MEXICO
The Borderlands and Climate Change 267

(Left) Water from a flash flood flowing along the border fence 

and through the port of entry at Organ Pipe Cactus National 

Monument, Arizona, and Sonoyta, Sonora, July 2008

(Above) Damage from the 2006 floods and mudslides in El Paso, 

Texas

Scientific alliance between United States and Mexican Federal agencies is needed to develop common scientific standards

for sharing environmental data and developing environmental indicators, to monitor environmental consequences of climate 

change, and to develop mitigation plans for both the United States–Mexican border region specifically and North America in

general. For example, at the current population, per capita water availability in the Rio Grande watershed is estimated to be 

1,467 cubic meters (m3

) (387,581.4 gallons [gal]) per person per year, which is between the acceptable limit (1,700 m3 [449,140 gal] 

per person per year) and the water scarcity limit (1,000 m3 [264,200 gal] per person per year) (as calculated by the Swedish 

hydrologist Malin Falkemark; Patino, 2005). Climate change and increased population will force both Federal and local 

governments to search for innovative solutions to manage scarce water resources, and providing both United States and Mexican 

scientists with the data and modeling tools to develop binational solutions is the first step to develop these alternative solutions.

Several federally funded binational information and research collaborations are currently laying the groundwork for improved 

water management of the Rio Grande watershed, such as the USGS Border Environmental Health Initiative and United States–

Mexico Border Geographic Information System, the Transboundary Aquifer Assessment Program, and the Physical Assessment 

Project for the Rio Grande watershed.

When a hazard strikes the Borderlands, damage to either country affects the other, in both economic and societal ways. 

During the August 2006 monsoon activity, 35.1 cm (13.8 in) of rain fell over the El Paso–Ciudad Juárez sister city area in a 

2-week period. During the storm, several earthen dams in the Sierra de Juárez were in danger of collapsing; because of the steep 

topography, the flood waters had the potential to inundate downtown El Paso. Analysis of the changes to the urban landscape,

such as increased development of unplanned communities on the margins of Ciudad Juárez, coupled with peak surface runoff of 

surface waters, almost resulted in critical economic loss for El Paso. The sharing of technologically sophisticated mapping tools, 

such as light detection and ranging (LIDAR) imaging, and risk and vulnerability methodology, such as the Community 

Vulnerability Assessment Tool (CVAT), is critical for analyzing and mitigating the risks of flood hazards on both sides of the

border (see chapter 8).
268 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

 USGS Capabilities

Identifying and understanding the connections between multiple causes and effects are 

especially important in decisions that require anticipating the interactive effects of changes 

in climate and changes in resource management. The USGS occupies a strong position in the 

United States climate science community. The observation and research networks maintained 

by the USGS allow research scientists to monitor and interpret the interactions of climate 

change with ongoing changes in land, water, and biological resources. The multidisciplinary 

scientific expertise of the USGS—spanning geology, biology, hydrology, and geography—

enables the USGS to deliver to the managers of the Nation’s lands, waters, and ecosystems 

uniquely integrated information, predictive scenarios, and technological tools for response to 

climate change. These capabilities will become a major component in government response to 

the emerging need for information about interdependent resource effects of climate change.

Multidisciplinary Research

The USGS conducts research and monitoring efforts to identify and understand critical 

interdependencies between climate, land use, and management decisions in the response 

of natural resources including water, energy, and ecosystems. Challenging research efforts 

such as those focusing on the effects of the El Niño phenomenon on Southwest regional 

streamflow, lake levels, and landslide

potential have broad implications for 

climate change monitoring and response. 

The El Niño phenomenon is perhaps the 

best-studied example of a global climate 

change, having coherent influences that

arise from recognized physical origins, 

and it is also of a scale that is comparable 

to much of the greenhouse change 

projected in climate-model experiments, 

both spatially and in terms of the 

magnitude of temperature deviations. 

The ways in which water and land 

resources are managed and maintained 

in the presence of ENSO-like variability 

provide snapshots of the kinds of 

responses that might be necessary in a 

warming world (Reynolds and others, 

1997; see also Arnow and Stephens, 1990; 

Cayan and Webb, 1992; Glantz, 1996; 

Wieczorek, 1996).
The Borderlands and Climate Change 269

 Red-winged Blackbird 

(Agelaius phoeniceus)
270 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

The USGS also researches the interactions among climate, land-use change, human-caused 

disturbances on ecosystems and their biota, natural hazards and their effects, water availability 

and quality, and exposure of humans and biota to disease. This research can identify thresholds 

of environmental change and address the social and ecological risks associated with crossing 

these thresholds. In order to evaluate the potential effects of climate change on the Borderlands, 

the regional climate change projections should be scaled down to something approaching the 

county scale. These climate change projections can then be used to produce products such 

as aridity index maps (calculated as the ratio of average annual precipitation to potential 

evapotranspiration) for the Borderlands to help identify where water resources and natural 

habitat will be stressed in different climate change projections.

To address the issue of rising levels of carbon dioxide (CO2

), the USGS studies geologic 

options for storing CO2 in depleted oil and gas reservoirs, deep coal seams, and saline formations. 

The USGS methodology to assess the Nation’s resources for geologic carbon sequestration 

estimates storage resource potential as volume of pore space into which CO2 can be injected 

and retained for tens of thousands of years, and it can be applied uniformly to geologic formations 

across the United States. The storage resources are accessible through present-day geological 

and engineering knowledge and technology. No economic factors are used in the estimation of 

the volume of storage resource. For more information on the USGS and geologic carbon 

sequestration, see http://energy.usgs.gov/HealthEnvironment/EnergyProductionUse/

GeologicCO2Sequestration.aspx. 

floods
The Borderlands and Climate Change 271

Product Development

The USGS provides high-resolution spatial climate and ecosystem model results for public 

lands and for use by land managers. We are developing a public-access delivery system for 

integrated geospatial data that can be used to delineate ecosystems and evaluate effects. We also 

develop predictive and adaptive tools and strategies for managers to use to reduce the risks of 

hazards as well as increase the potential for hydrologic and ecological systems to be self-sustaining 

and resilient to climate change and related disturbances.

References cited in this are listed in chapter 12.

drought
An Opportunity and an Imperative

By Randall G. Updike and William R. Page

Along the nearly 3,200 kilometers (almost 2,000 miles) of the United 

States–Mexican border, we are witnessing the expression of the challenges 

of the 21st century. The Borderlands have become a microcosm for the 

entire United States and Mexico; the issues faced in that region are felt 

throughout both nations—water availability and quality, ecosystem health, 

natural resource needs, safety from natural hazards, and human 

socioeconomic well-being. If these issues were not challenging enough, 

we now recognize that the difficulties of addressing them are exacerbated 

by the onset of climate change, and as we come to better understand the 

complexities of the components of these challenge themes, we discover 

that each part is inextricably intertwined with other overarching issues. 

Further, because we are a creative and progressive society, we all seek to 

understand and appreciate the natural environments associated with the 

Borderlands while at the same time benefitting from the region’s many 

social and economic values. It is little wonder that we as a society find 

it increasingly difficult to ask the right questions, much less find suitable 

answers to the questions we do ask. For the many scientists who have 

worked in the Borderlands and contributed to the preceding chapters, 

this circular is a way to describe to the two nations of the region the 

capabilities the U.S. Geological Survey can provide to assist in that 

quest for knowledge and understanding in preparation for the future.

Chapter 11

U.S. Geological Survey 

scientist collecting a 

water-quality sample from 

Loma Verde Wash in Saguaro 

National Park, Arizona, as part 

of the multidisciplinary USGS 

Amphibian Research and 

Monitoring Initiative

U.S. Geological Survey scientist preparing a sample within a glove box to test the effect of antibiotics 

on denitrifying bacteria

274 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Though the mission of the U.S. Geological Survey (USGS) is not to serve as land manager, law enforcer, or code regulator, 

its innovation and creativity and the scientific and technical depth of its capabilities can be directly applied to monitoring the

conditions of the landscape. The ability of USGS scientists to critically analyze the monitored data in search of signals and 

trends, whether they lead to negative or positive results, allows us to reach significant conclusions—from providing factual

conclusions to decisionmakers, to estimating how much of a natural resource exists in a particular locale, to predicting how a 

natural hazard phenomenon will unfold, to forecasting on a scale from hours to millennia how ecosystems will behave.

Fortunately, both Mexico and the United States are beginning to recognize the urgency needed in responding to the challenges 

described in these chapters. Land management agencies, natural resource entities, political and social leaders, and private citizens 

are facing tomorrow’s challenges by taking the initiative to search for solutions. The USGS offers a wealth of capabilities in 

support of that goal, and though some of our partners in our applied science efforts are other Federal agencies, we also seek to 

collaborate with State and local partners, associations, State and county governments, nongovernmental organizations, and our 

counterparts in Mexico at both the Federal and State levels.

One outcome of the discussions offered in this circular would be to encourage the 

development of strategic and multidisciplinary solutions to problems with local to far-reaching 

scopes. To this end, the USGS approaches collaboration with our present and future partners 

in the Borderlands with three goals: (1) develop a basic understanding of the specific issues

and concerns facing Federal, State, and local governments and private entities; (2) recommend 

ways to address these issues and concerns; and (3) carry out investigations that help to 

address each specific border issue.

U.S. Geological Survey emeritus Gordon Haxel (Flagstaff) (with Bob Powell, Tucson, right) explaining 

the geology of the Baboquivari Mountains, Arizona
Dr. Janet Ruth of the Fort Collins Science Center, U.S. Geological 

Survey, studying wintering grassland birds in southeastern 

Arizona with the help of local student volunteers. Dr. Ruth 

conducted research over several years in cooperation with 

the Bureau of Land Management, U.S. Forest Service, U.S. Fish 

and Wildlife Service, National Audubon Society, and private 

landowners. For more information on this project, see 

http://www.fort.usgs.gov/HerdingSparrows/.

Grasshopper Sparrow (Ammodramus savannarum)

(Above) Boreholes being 

drilled at Cinder Lake in 

Coconino National Forest, 

Arizona, as part of a U.S. 

Geological Survey study to 

determine the lake’s floodwater 

storage capacity. The lake 

has been used to store runoff 

from nearby areas affected by 

wildfire.
276 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

This circular identifies several challenge themes associated with the United States–Mexican border 

region—ecological resources, water availability and quality, environmental and human health, people in 

the Borderlands, energy and mineral resources, natural hazards, and border security and environmental 

protection. Climate change is also discussed, as it influences the course of all of these issues. The discussion 

for each theme has focused on how the USGS can work with cooperating agencies to improve understanding 

of the issues, which can then lead to action and hopefully to collaborative solutions. The table on the 

following pages reviews the eight issues covered in this circular and summarizes what we, the USGS, 

consider to be our essential core responsibilities in addressing each of these challenges. Below are some 

brief highlights of just a few of the ways the USGS uses our multidisciplinary science to meet these core 

responsibilities.

Water availability is one of the most important issues in the Borderlands because it is 

intertwined with the socioeconomic well-being of communities, with ecosystem diversity, and 

with the survival of unique species. Hydrologic capabilities of the USGS address the water 

issues of these complex systems through monitoring, characterization, and modeling activities. 

Issues related to energy and mineral resources include supply and demand, competing 

land uses, and the environmental consequences of resource management. The USGS addresses 

these issues through resource predictive modeling, monitoring, and assessment activities. 

Protecting the environment, safeguarding human health, 

and understanding and mitigating the effects of human activity 

in the Borderlands are challenged by stressors such as 

overpopulation, inadequate infrastructure, water shortages, 

elevated rates of communicable disease, and contaminants in 

air, soil, and water. In addition to water quality monitoring, the 

USGS leads in the development of environmental indicators 

and human health geospatial analyses. 

The Borderlands region boasts the highest diversity of desert plants and one of the 

largest number of bird species in the world. Increases in human populations and associated 

changes in land use, however, threaten this diversity by contributing to the fragmentation and 

loss of ecosystem habitats. The USGS uses state-of-the-art research to address habitat loss 

and fragmentation; projects include developing ecological indicators, conducting baseline 

biologic inventories, and determining the effects of climate change on ecosystems by mapping 

and monitoring vegetation and habitats across the United States–Mexican border region. 
An Opportunity and an Imperative 277

Rapid population and economic growth and the problem of undocumented border crossings 

present challenges for the management of border security and environmental protection among 

the unique natural resources of the Borderlands. To help protect these resources, the USGS 

has developed binational, integrated science datasets to support the border and environmental 

security and management activities of Federal, State, and local agencies. 

Natural hazard risks such as earthquakes, landslides, wildfires, hurricanes, and flash floods

threaten communities and infrastructure along the border. The USGS possesses advanced 

capabilities to monitor natural hazards, analyze levels of risk and vulnerability, and provide 

risk assessment data to emergency response officials, resource managers, and the public to help

reduce property damage, injury, and loss of life. 

Perhaps the most perplexing issue facing the Borderlands is climate change and how it 

could affect the region. Because it is a far-reaching and long-term concern, climate change 

will continue to have an increasing influence on all of the Borderlands challenge themes. The

USGS is vigorously developing its climate change science program to assess the overall effects 

on society and ecosystems, not only in the Borderlands, but throughout the world as well. 

Forecasting environmental change on decadal scales—such as precipitation, water availability, 

changes in seasonality, and the response of living organisms—will be critical to successfully 

addressing each of the Borderlands challenge themes.

borderlands challenge themes
278 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Table 11–1. Summary of the issues faced in the United States–Mexican border region within each of the challenge themes used in this 

report and the strategic goals adopted by the U.S. Geological Survey to address those issues.

Issues Strategic Goals

Ecological Resources

The Borderlands have the highest diversity of desert plants 

in the world and host critical migration routes for the 

largest number of bird species in North America. 

Because many of these species reside at their northernmost 

extents, they are at particular risk of habitat loss due to 

stressors such as climate change and human activities, 

including population growth, industry, mining, and 

agriculture.

Conduct research through monitoring and mapping activities 

that would assist resource managers prevent species 

loss, help recover and protect habitat, predict the effects 

of invasive species, and provide resource management 

expertise through biological, social, and economic 

analyses of conservation policy and management 

practices.

Water Availability and Quality

Much of the water resources of the Borderlands are 

extremely limited because of its low precipitation and 

semiarid to arid environments, the over-allocation of 

water rights from past international treaties, and water 

budget deficits where withdrawls exceed limited aquifer

recharge. 

Many populated parts of the Borderlands also have dire 

water quality problems, including significant microbial

and chemical contamination from sewage and 

agricultural runoff.

Assist land and water resource managers at all levels of 

government in assuring transboundary water availability 

and quality by conducting research through monitoring, 

characterization, predictive modeling, and water quality 

analyses and by developing new methods and techniques 

to understand and solve water resource problems, in this 

way supporting population growth and economic 

prosperity while protecting the natural environment.

Environment and Human Health

Water shortages and pollution, poor air quality, increased 

soil salinities, and pesticides and heavy-metal contaminants 

are some of the many stressors that contribute to 

degradation of the quality of life in the Borderlands. 

Lack of water treatment infrastructure along many parts 

of the border has led to elevated rates of chronic and 

communicable disease.

Conduct long-term water quality and biota monitoring and 

modeling, perform land use and land cover analyses, 

develop environmental indicators, and provide database 

development and geospatial analyses in both 

environmental and human health fields to help ensure

quality of life in the Borderlands.

People in the Borderlands

Rapid population growth has contributed to increased 

environmental stressors in the Borderlands and has led 

to unplanned development, which has negatively affected 

ecosystems, natural resources, and quality of life. 

Native American cultural sites and resources are rapidly 

being lost to vandalism and trafficking of artifacts.

Develop and maintain binational geographic information 

systems and natural resource databases, and establish 

baseline datasets for monitoring and conducting landscape 

change analyses to assist researchers, government 

officials, planners, and concerned citizens in mitigating

human activities that adversely affect the environment 

and human and wildlife health in the Borderlands.

issues goals
An Opportunity and an Imperative 279

Issues Strategic Goals

Energy and Mineral Resources

With global and domestic demand for energy and mineral 

(precious metal and rare earth) resources increasing, the 

abundance of these resources in the Borderlands will make 

it an important area for development well into the future.

There are approximately 11,000 abandoned mine sites in 

the Borderlands. Legacy heavy metal contamination and 

other toxic materials have resulted in water, soil, and 

air pollution; habitat destruction; and adverse effects on 

human and wildlife health.

Conduct energy and mineral resource modeling, monitoring, 

and environmental assessment, and provide unbiased 

resource data to help guide policy decisions concerning 

sustainable and responsible resource development and to 

assess and evaluate abandoned mines and waste dumps 

in order to understand potential effects on human and 

wildlife health.

Natural Hazards

Earthquakes, landslides, wildfires, hurricanes, and intense

flash floods occur frequently in the Borderlands and

have resulted in millions of dollars in property and 

infrastructure damage, the destruction of ecosystem 

habitats, and significant injury and loss of life.

Collaborate with Federal, State, and local agencies to 

minimize the effects of natural hazards by providing 

timely, unbiased science information to emergency 

response officials, resource managers, and the public

to help reduce the loss of life, injuries, and property 

damage from natural hazards. 

Improve hazard predictions, analyze risk and vulnerability 

for disaster prone areas, develop a national risk monitoring 

program, and mobilize response efforts during and after 

a natural disaster event to provide technical counsel on 

recovery and response.

Border Security and Environmental Protection

Illegal crossings and human and drug smuggling activities

occur daily at numerous locations along the United 

States–Mexican border. 

These activities have created significant security challenges

to both nations and have adverse effects on natural 

resources and fragile wildlife habitat.

Develop a collaborative effort between United States and 

Mexican officials at all levels of government to collect

information and provide a binational geographic 

information system containing environmental and 

socioeconomic datasets to assist in improving border 

protection and security and developing state-of-the-art 

techniques to assure greater overall security along the 

United States–Mexican border while protecting the 

environment.

Climate Change

Climate change projections have shown that parts of the 

Borderlands may be particularly vulnerable to climate 

change because of low precipitation and extreme 

temperatures, which may lead to adverse effects on 

humans and ecosystems by increasing the potential for 

more droughts, heat waves, water shortages, wildfires,

poor air quality, disease, and flooding.

Meet the needs of policy makers, resource managers, 

communities, and ecosystems by conducting research 

and monitoring and modeling activities to evaluate and 

assess the effects of climate change and by developing 

predictive and adaptive tools and strategies to reduce the 

risk of hazards and increase the potential for communities 

and ecosystems to be self-sustaining and resilient to the 

adverse effects of climate change.

An Opportunity and an Imperative 281

Dancers with the Baile Espanol de Santa Fe perform a folklórico, 

a traditional Latin American dance, at a Hispanic Heritage Month 

celebration in New Mexico. Events such as this held throughout 

the Borderlands help to bring the region’s people together and 

highlight the culture, and the home, that they share.

For more than one hundred years the Borderlands environment was able to exist somewhat unaffected by the scattered 

occupation of humans who demanded little from the land and exerted little influence in return. The marks of man’s activities were

only fine scratches on an expansive, wild panorama, but with the recognition that natural resources abounded in the Borderlands,

that water, though apparently scarce, could be obtained, and that the land could support extensive agriculture and burgeoning 

cities, the fine marks became bold strokes. The most powerful change, however, has been the converging and blending of the

Mexican and American populations in the Borderlands, coalescing into a unique Borderlands society. Inexpensive labor has 

fueled expansive urban sprawl, and supply and demand for products and people, both legal and illicit, have overrun the natural 

environment along many segments of the border, inhibiting the environment’s ability to recover from human activity.

The USGS has a long history of providing reliable science information to work toward the resolution of important 

environmental and societal issues. The interdisciplinary science programs of the USGS and the breadth and depth of expertise 

of our researchers yield unique and unbiased perspectives on how such issues can be addressed throughout the Borderlands.
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All cited works published by the U.S. Geological Survey are indicated 

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U.S. Geological Survey series reports can be found through the 

USGS Publications Warehouse at http://pubs.er.usgs.gov/. 

Chapter 12
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284 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Chapter 1

The United States–Mexican Border—

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Chapter 3

Challenge Theme 1. Understanding and Preserving 

Ecological Resources

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Chapter 4

Challenge Theme 2. Assuring Water Availability 

and Quality in the 21st Century

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Chapter 7

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Chapter 8

Challenge Theme 6. Natural Hazard Risks 

in the Borderlands

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Chapter 9

Challenge Theme 7. Information Support for 

Management of Border Security and 

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Credits

“. . . .facing the challenge” Author Credits

Chapter 4

Challenge Theme 2. Assuring Water Availability and Quality in the 21st Century

Estimation of Aquifer Thickness in the 

Mimbres Groundwater Basin, New Mexico, 

Using Gravity (page 78 ) ...................................................................................................................................... Charles E. Heywood

Capture Maps Help Water Managers Understand 

the Effects of Groundwater Pumping on Streams, 

Springs, and Riparian Vegetation (page 84 ) ............................. Stanley A. Leake, Donald R. Pool, and James M. Leenhouts

The Use of Semipermeable Membrane Devices 

to Assess Organic Compounds in the Rio Grande 

from Presidio to Brownsville, Texas (page 90 ) ..........................................................................J. Bruce Moring and Rita Setser

Chapter 6

Challenge Theme 4. People in the Borderlands

AGAVES—Assessment of Goods and 

Valuation of Ecosystem Services in the 

San Pedro River Basin, United States 

and Mexico (page 142)..........................................................................................................................................

Darius J. Semmens, Nita Tallent-Halsell, David C. Goodrich, 

Laura M. Norman, Charles van Riper III, Robert Winthrop, 

William G. Kepner, David Brookshire, D. Philip Guertin, 

and Malka Pattison

. . . .facing the challenge

. . . .facing the challenge
United States–Mexican

. . . . .facing tomorrow’s challenges through USGS science

Circular 1380

U.S. Department of the Interior

U.S. Geological Survey

Borderlands

Printed on recycled paper

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44	 Gilded flicker—Photo by Cullen Photos—Fotolia; purchased license

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54 Prickly pear—Photo by Diana Papoulias, U.S. Geological Survey

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Chapter 4

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65 Two horses—Photo by Daniel Pearson, U.S. Geological Survey

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86 Sampler background—Photo by M. Eckenwiler, U.S. Geological Survey

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Chapter 5

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110 C. immitis—Photo by U.S. Army Medical Department

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112 Sediment core—Photo by U.S. Geological Survey

113 Arroyo Colorado—Photo by National Oceanic and Atmospheric Administration

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117 Downtown Yuma, Arizona—Photo by Ken Lund—Flickr; Creative Commons Attribution–

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120 Report—U.S. Executive Order 12898 

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122 Maquiladora—Photo by Guldhammer—Wikimedia Commons; public domain

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135 Canal sunset— Photo by U.S. Bureau of Reclamation

135 Building construction—Photo by soleilc1—Fotolia; purchased license

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138 Vista—Photo by National Park Service

139 Harbor—Photo by Rudy Schuster, U.S. Geological Survey

140–141 Landscape—Photo by Galyna Andrushko—Fotolia; purchased license

143 San Pedro River—Photo by Jerry Jacka—Used with permission

144 Girl with feather—Photo by Maze Walker—Flickr; Creative Commons Attribution–NonCommercial–

NoDerivs 2.0 Generic

144 Petroglyph—Photo by Daniel Pearson, U.S. Geological Survey

144 Man in hat—Photo by biotour13—Flickr; Creative Commons Attribution–NonCommercial–NoDerivs 

2.0 Generic

144 Farm—Photo by biotour13—Flickr; Creative Commons Attribution–NonCommercial–NoDerivs 2.0 

Generic

145 Petroglyph—Photo by ColoApril—Flickr; Creative Commons Attribution–NonCommercial–NoDerivs 

2.0 Generic

145 Basketmaker—Photo by U.S. Bureau of Reclamation; National Archives and Records Administration

145 Woman—Photo by biotour13—Flickr; Creative Commons Attribution–NonCommercial–NoDerivs 

2.0 Generic

146 Fish—Photo by Nicholas Paretti, U.S. Geological Survey

146 Report—U.S. Geological Survey Fact Sheet 2010–3097

146 Data collection—Photo by James Callegary, U.S. Geological Survey

147 Petri dish—Photo by Centers for Disease Control and Prevention

147 Bacteria cluster—Photo by Eric Erbe and Christopher Pooley, U.S. Department of Agriculture, 

Agricultural Research Service
Credits 311

147 Report—U.S. Geological Survey Circular 1322

148 Desert—Photo by Paul Moore—Fotolia; purchased license

150 Roadrunner—Photo by sekarb—Fotolia; purchased license

150 Cactus—Photo by Ptah2006—Fotolia; purchased license

151 River—Photo by B Jefferson Bolender—Flickr; Creative Commons Attribution–NonCommercial–

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152 Girls—Photo by Eva Lemonenko— Fotolia; purchased license

153 Vaqueros—Photo by Eva Lemonenko— Fotolia; purchased license

153	 Report—U.S. Geological Survey Scientific Investigations Report 2012–5066

Chapter 7

Page

155 Lavender Pit—Photo by Cornellrockey—Wikimedia Commons; Creative Commons Attribution–

Share Alike 2.5 Generic

156–157 Aerial—Photo by member of Expedition 16 crew, National Aeronautics and Space Administration

157	 Report—U.S. Geological Survey Scientific Investigations Report 2010–5090–A

159 Copper—Photo by Rob Lavinsky, iRocks.com—Wikimedia Commons; Creative Commons 

Attribution–Share Alike 3.0 Unported

160 Cananea—Photo by Alberto Quiñones—Flickr; Creative Commons Attribution–NonCommercial–

NoDerivs 2.0 Generic

161 Cananea then—Photo by Southern Methodist University, Central University Libraries, DeGolyer 

Library—Flickr; public domain

161 Cananea now—Photo by Fernwer—Wikimedia Commons; Creative Commons Attribution–

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162–163 Cement facility—Photo by brianguest—Fotolia; purchased license

162 Surface mining—Photo by Diana Papoulias, U.S. Geological Survey

162 Warning sign—Photo by Wild Geese—Fotolia; purchased license

165 Gold—Photo by Alchemist-hp—Wikimedia Commons; Creative Commons Attribution–

NonCommercial–NoDerivs 3.0 Unported

165 Silver—Photo by Alchemist-hp—Wikimedia Commons; Creative Commons Attribution–Share Alike 

3.0 Unported

165 Copper—Photo by Rob Lavinsky, iRocks.com—Wikimedia Commons; Creative Commons Attribution–Share Alike 3.0 Unported

165 Lead—Photo by Alchemist-hp—Wikimedia Commons; Creative Commons Attribution–

NonCommercial–NoDerivs 3.0 Unported

165 Zinc—Photo by Alchemist-hp—Wikimedia Commons; Creative Commons Attribution–

NonCommercial–NoDerivs 3.0 Unported

166 Drainage—Photo by Floyd Gray, U.S. Geological Survey

167 Landscape—Photo by B Jefferson Bolender—Flickr; Creative Commons Attribution–Noncommercial–

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167 Sunset—Photo by B Jefferson Bolender—Flickr; Creative Commons Attribution–

Noncommercial 2.0 Generic

168 Drill rig—Photo by Jessica K. Robertson, U.S. Geological Survey

168 Report—U.S. Geological Survey Fact Sheet 2011–3020

171 Background—Photo by photosoup—Fotolia; purchased license

171 Coal cars—Photo by Ivars Linards Zolner—Fotolia; purchased license

172 Oil drum—Photo by Gudellaphoto—Fotolia; purchased license

173 ASARCO plant—Photo by Iose—Wikimedia Commons; public domain

173 Bisbee—Photo by F.L. Ransome, U.S. Geological Survey

174 Oil sample—Photo by Leslie C. Gordon, U.S. Geological Survey

174 Strip mine—Photo by Lyntha Scott Eiler, U.S. Environmental Protection Agency—National Archives 

and Records Administration; public domain
312 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

174 Oil spill—Photo by forcdan—Fotolia; purchased license

175 Background—Photo by National Oceanic and Atmospheric Administration, National Ocean Service

175	 Oil rig fire—Photo by U.S. Coast Guard

176 Silver Bell mine—Photo by Robert Kamilli, U.S. Geological Survey

177 Reports—U.S. Geological Survey Fact Sheet 2004–3007 (English and Español)

178 Report—U.S. Geological Survey General Information Product 123

178 Core sample—Photo by Dennis Demcheck, U.S. Geological Survey

178 Sample collection—Photo by Lori Lewis, U.S. Geological Survey

179 Oil rig sunset—Photo by Leonid Ikan—Fotolia; purchased license

Chapter 8

Page

181 Landslide—Photo by Mark Reid, U.S. Geological Survey

182 Telephone lines—Photo by Los Angeles Times—University of California–Los Angeles Library; 

Creative Commons Attribution–Noncommercial–Share Alike 3.0 United States

182 Field—Photo by D. Cavit, U.S. Geological Survey

183 Background—Photo by Olivier MARTIN—Fotolia; purchased license

183 Columns—Photo by C.E. Johnson, U.S. Geological Survey

184 Bowling alley—Photo by Lindie Brewer, U.S. Geological Survey

184 Surface rupture—Photo by crosby_cj—Flickr; Creative Commons Attribution–NonCommercial–

NoDerivs 2.0 Generic

186 Poster—U.S. Geological Survey earthquake summary map

188–189 Fault ruptures—Photo by Ken Hudnut, U.S. Geological Survey

190 Sabino Canyon—Photo by Chris Magril, U.S. Geological Survey

191 Laguna Beach—Photo by Jim Bowers, U.S. Geological Survey

191 Montezuma Canyon—Photo by National Park Service

191 Report—U.S. Geological Survey Fact Sheet 2012–3008

192–193 Photo from Adobe/Getty Images

193	 Wildfire—Photo by Andrea Booher, Federal Emergency Management Agency—National Archives

and Records Administration

194	 After the fire—Photo by Ray Kokaly, U.S. Geological Survey

194	 California wildfires—Photo by National Aeronautics and Space Administration

195 Burned landscape—Photo by U.S. Geological Survey

195 Report—U.S. Geological Survey Open-File Report 2007–1384

196 Runoff—Photo by U.S. Bureau of Reclamation

196 Flood—Photo by National Oceanic and Atmospheric Administration

197 Claudette—Photo by Jacques Descloitres, National Aeronautics and Space Administration

199 Beulah satellite—Photo by National Oceanic and Atmospheric Administration

199	 Beulah floods—Photo by National Oceanic and Atmospheric Administration

200 Development—Photo by Jean Parcher, U.S. Geological Survey

201 Pavement—Photo by monjiro—Fotolia; purchased license

202 Report—U.S. Geological Survey Fact Sheet 2010–3036

202 Report—U.S. Geological Survey Circular 1324

202 Report—U.S. Geological Survey Circular 1306

203 Wall—Photo by javarman—Fotolia; purchased license
Chapter 9

Page

205 Fence—Photo by U.S. Army Corps of Engineers

206 Aircraft—Photo by Gerald L. Nino, U.S. Customs and Border Protection

206 Fence—Photo by U.S. Customs and Border Protection

206 Sign—Photo by Rusty Dodson—Fotolia; purchased license

207 Immigrants—Photo by U.S. Fish and Wildlife Service

207 Marijuana—Photo by U.S. Fish and Wildlife Service

207 Opium patrol—Photo by Los Angeles Times—University of California–Los Angeles Library; 

Creative Commons Attribution–Noncommercial–Share Alike 3.0 United States

208 San Ysidro—Photo by Wbaron01—Wikipedia; Creative Commons Attribution 3.0

210 USGS Scientist—Photo by Amy Clymer, U.S. Northern Command

211 Tunnel map—Photo by Drug Enforcement Administration

211 Boxes—Photo by Drug Enforcement Administration

212 Rotor background—Photo by Darz Mol—Wikimedia Commons; Creative Commons Attribution–

Share Alike 3.0 Unported

212 Children—Photo by Los Angeles Times—University of California–Los Angeles Library; 

Creative Commons Attribution–Noncommercial–Share Alike 3.0 United States

212 Training—Photo by Staff Sgt. Mark Johnson, U.S. Air Force

213 Pronghorn—Photo by Michael Ireland—Fotolia; purchased license

213 Bighorn sheep—Photo by Magnus Kjaergaard—Wikimedia Commons; Creative Commons 

Attribution 3.0 Unported

213 Trash—Photo by Bruce Gungle, U.S. Geological Survey

214–215 Calexico-Mexicali—Photo by ImageShack—Wikimedia Commons; Creative Commons Attribution–

Share Alike 3.0 Unported

214 Ferry—Photo by W.C. Mendenhall, U.S. Geological Survey

214 Inspection then—Photo by Los Angeles Times—University of California–Los Angeles Library; 

Creative Commons Attribution–Noncommercial–Share Alike 3.0 United States

214 Crossing 1950 (2)—Photos by Los Angeles Times—University of California–Los Angeles Library; 

Creative Commons Attribution–Noncommercial–Share Alike 3.0 United States

215 Station sign—Photo by Omar Barcena—Flickr; Creative Commons Attribution 2.0 Generic

215 Port of entry—Photo by Wbaron—Wikipedia; Creative Commons Attribution–Share Alike 3.0

215 Inspection now—Photo by Josh Denmark, U.S. Customs and Border Protection—Flickr; 

Creative Commons Attribution¬–Share Alike 2.0 Generic

216 Trash—Photo by U.S. Fish and Wildlife Service

217 Buenos Aires fence (2)—Photo by U.S. Fish and Wildlife Service

217 San Diego fence—Photo by Randy Schuster, U.S. Geological Survey

217 Canal fence—Photo by U.S. Army Corps of Engineers

217 Debris fence—Photo by National Park Service

218 Scientists—Photo by U.S. Geological Survey

218 Surveillance tower—Photo by James Tourtellotte, U.S. Customs and Border Protection

218 Fire cleanup—Photo by Department of Homeland Security

219 Reports—U.S. Geological Survey Fact Sheet 2008–3069 (English and Español)

224–225 Horses—Photo by James Tourtellotte, U.S. Customs and Border Protection

224 ATVs—Photo by James Tourtellotte, U.S. Customs and Border Protection

224 National Guard—Photo by Sgt. Jim Greenhill, U.S. Army

225 Border Patrol—Photo by Gerald L. Nino, U.S. Customs and Border Protection

225 Medallion—Photo by James Tourtellotte, U.S. Customs and Border Protection

Credits 313
228–229 Blackhawks—Photo by James Tourtellotte, U.S. Customs and Border Protection

230 Water fountain—Photo by Phase4Photography—Fotolia; purchased license

232–233 Fence—Photo by Jim Parkin—Fotolia; purchased license

Chapter 10

Page

235 Earth—Photo by Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, National Aeronautics 

and Space Administration

236 Beach fence—Photo by James Reyes—Wikimedia Commons; public domain

236 Sea turtle—Photo by U.S. Fish and Wildlife Service

236 Causeway—Photo by Dhruvaraj S—Flickr; Creative Commons Attribution 2.0 Generic

238 River—Photo by Daniel Pearson, U.S. Geological Survey

238 Storm—Photo by Daniel Pearson, U.S. Geological Survey

240–241 Rainbow—Photo by Bruce Moring, U.S. Geological Survey

240 Sunset—Photo by Dand8282—Wikimedia Commons; Creative Commons Attribution–Share Alike 3.0 

Unported

240 Highway—Photo by Eu Toch—Fotolia; purchased license

242 Clouds—Photo by Daniel Pearson, U.S. Geological Survey

242 Sierra Madre—Photo by Christian Frausto Bernal—Flickr; Creative Commons Attribution–

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243 Lightning—Photo by valdezrl—Fotolia; purchased license

244 Monsoon—Photo by Rsduhamel—Wikimedia Commons; Creative Commons Attribution–

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244 Fire suppression—Photo by Johannes Cater—Wikimedia Commons; public domain

245 Douglas—Photo by Jacques Descloitres, National Aeronautics and Space Administration

246	 Pacific Ocean—Image by U.S. Geological Survey

246 Rough waves—Photo by National Oceanic and Atmospheric Administration

247 Snowmelt—Photo by Rocky Mountain National Park, National Park Service

247 Beetle—Photo by U.S. Forest Service

247 Beetle-kill bark—Photo by U.S. Forest Service

247 Beetle-kill forest—Photo by Heather Lammers, National Renewable Energy Laboratory

248 Dust storm—Photo by Library of Congress

248 Drought—Photo by Los Angeles Times—University of California–Los Angeles Library; 

Creative Commons Attribution–Noncommercial–Share Alike 3.0 United States

248 Lake drought—Photo by Travis Dowell, U.S. Geological Survey

250–251 River valley—Photo by Erin and Lance Willett—Flickr; Creative Commons Attribution–

NonCommercial–NoDerivs 2.0 Generic

250 Docks on river—Photo by Don Barrett—Flickr; Creative Commons Attribution–NonCommercial–

NoDerivs 2.0 Generic

251 River marsh—Photo by Chris Austin—Flickr; Creative Commons Attribution–NonCommercial–

NoDerivs 2.0 Generic

252 Prickly pear—Photo by Diana Papoulias, U.S. Geological Survey

253	 Windmill—Photo by Leaflet—Wikimedia Commons; public domain

253	 Firefighter—Photo by U.S. Forest Service

254 Rio Grande—Photo by J.N. Stuart—Flickr; Creative Commons Attribution–NonCommercial–

No Derivative Works 2.0 Generic

255 Lake Mead (2)—Photos by slgwv—Flickr; Creative Commons Attribution–NonCommercial 2.0 

Generic

255 Bluebonnet—Photo by J. Axel, National Park Service

257 Algae in lake—Photo by Nara Souza, Florida Fish and Wildlife Commission—U.S. Geological Survey 

Multimedia Gallery

314 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
257 Algae colony—Photo by Barry H. Rosen, U.S. Geological Survey

257 Dust storm—Photo by National Weather Service

258–259	 Dust storm—Photo by Leaflet—Wikimedia Commons; public domain

260 Abandoned mine—Photo by Dan Mosier, U.S. Geological Survey

261 San Diego—Photo by Doug Letterman—Flickr; Creative Commons Attribution 2.0 Generic

265 Background—Photo by Wiz Works Photo—Fotolia; purchased license

265 Drought—Photo by Tim Keegan—Flickr; Creative Commons Attribution–Share Alike 2.0 Generic

265 Burn area—Photo by John G. Elliott, U.S. Geological Survey

266 El Paso–Juárez—Photo by National Aeronautics and Space Administration

267 Mudslide—Photo by Robert J. Alvey, Federal Emergency Management Agency—National Archives 

and Records Administration

267	 Border flood—Photo by National Park Service

268–269 Storm—Photo by Paul Moore—Fotolia; purchased license

268 Report—U.S. Geological Survey Data Series 691

268	 Report—U.S. Geological Survey Scientific Investigations Report 2011–5103

268 Report—U.S. Geological Survey Circular 1331

268 Stream—Photo by Steve Hillebrand, U.S. Fish and Wildlife Service

269 Landscape—Photo by George Gentry, U.S. Fish and Wildlife Service

269 Blackbird standing—Photo by Bob Jagendorf—Flickr; Creative Commons Attribution–

NonCommercial 2.0 Generic

269 Blackbird clinging—Photo by Cephas—Wikimedia Commons; Creative Commons Attribution–

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269 Report—U.S. Geological Survey Fact Sheet 2008–3097

269	 Report—U.S. Geological Survey Scientific Investigations Report 2010–5233

270 Flood—Photo by PhotoAlex—Fotolia; purchased license

271 Drought—Photo by S Silver—Fotolia; purchased license

Chapter 11

Page

273 Girl—Photo by cliff1066—Flickr; Creative Commons Attribution 2.0 Generic

274 Water sampling—Photo by U.S. Geological Survey

274 Glove box sample—Photo by Jennifer C. Underwood, U.S. Geological Survey

274 Geologists—Photo by Robert K. Kamilli, U.S. Geological Survey

275 Borehole drilling—Photo by Jamie Macy, U.S. Geological Survey

275 Herding sparrows—Photo by Narca Moore-Craig—Used with permission

275 Sparrow—Photo by Dominic Sherony—Flickr; Creative Commons Attribution–

Share Alike 2.0 Generic

280–281 Folklórico—Photo by Paige Henderson—Flickr; Creative Commons Attribution–

NonCommercial–Share Alike 2.0 Generic

Chapter 12

Page

283 Yucca—Photo by Ritu Jethani—Fotolia; purchased license

Back Page

Page

318 Cross with date palm—Photo by Bruce Gungle, U.S. Geological Survey

Credits 315
316 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Poster

1 Condor—Photo by Phil Armitage—Wikimedia Commons; public domain

2 Landscape—Photo by Galyna Andrushko—Fotolia; purchased license

3 Palm fronds—Photo by Byron Moore— Fotolia; purchased license

4 Grey wolf—Photo by Marumari—Wikimedia Commons; Creative Commons Attribution–

Share Alike 3.0 Unported

5 Prickly pear—Photo by Diana Papoulias, U.S. Geological Survey

6 Lizard—Photo by Dschwen—Wikimedia Commons; Creative Commons Attribution–

Share Alike 3.0 Unported

7 Pelican close-up—Photo by Elizabeth Haslam—Flickr; Creative Commons Attribution–

NonCommercial 2.0 Generic

8 Irrigation—Photo by Brenda Carson—Fotolia; purchased license

9 Bridge—Photo by Matthew High—Flickr; Creative Commons Attribution–

NonCommercial 2.0 Generic

10 Two horses—Photo by Daniel Pearson, U.S. Geological Survey

11 Salt-encrusted tree—Photo by R. Scott Campbell—Fotolia; purchased license

12 Copper—Photo by Rob Lavinsky, iRocks.com—Wikimedia Commons; Creative Commons 

Attribution–Share Alike 3.0 Unported

13 Lavender Pit—Photo by Cornellrockey—Wikimedia Commons; Creative Commons 

Attribution–Share Alike 2.5 Generic

14 Sunset rig—Photo by Leonid Ikan—Fotolia; purchased license

15	 Rig with flag—Photo by Jessica K. Robertson, U.S. Geological Survey

16	 Girl with flag—Photo by cliff1066—Flickr; Creative Commons Attribution 2.0 Generic

17 Vaqueros—Photo by Eva Lemonenko— Fotolia; purchased license

18	 Firefighter—Photo by Andrea Booher, Federal Emergency Management Agency—

National Archives and Records Administration

19 Claudette—Photo by Jacques Descloitres, National Aeronautics and Space Administration

20 Wall crack—Photo by javarman—Fotolia; purchased license

21 Fence—Photo by U.S. Customs and Border Protection

22 Rotor—Photo by Darz Mol—Wikimedia Commons; Creative Commons Attribution–

Share Alike 3.0 Unported

23 Leaf in drought—Photo by S Silver—Fotolia; purchased license

24 Lightning—Photo by valdezrl—Fotolia; purchased license

25 Earth—Photo by Reto Stöckli, Nazmi El Saleous, and Marit Jentoft-Nilsen, 

National Aeronautics and Space Administration

316 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science
Credits 317

poster

Map Credits

Reference Map and GIS assistance by D. Paco VanSistine.

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318 United States–Mexican Borderlands. . . .facing tomorrow’s challenges through USGS science

Office of the Regional Director, Southwest Region

Publishing support provided by Denver Publishing Service Center

Edited by Melanie J. Parker

Layout and graphic design by Carol A. Quesenberry

For more information concerning this publication, contact:

Regional Director, Southwest Region

Box 25046, Mail Stop 911

Denver, CO 80225

(303) 236-5438