Ground-Water 

Resources of the 

Republic of 

El Salvador 

Central America

By A. N. SAYRE and G. C. TAYLOR, JR.

GEOLOGICAL SURVEY WATER-SUPPLY PAPER 1079-D

Geologic and hydrologic studies of water 

supply as a part of the program of the 

Health and Sanitation Division of El 

Salvador

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1951
i i

UNITED STATES DEPARTMENT OF THE INTERIOR 

Oscar L. Chapman, Secretary

I .

GEOLOGICAL SURVEY 

W. E. Wrather, Director

For sale by the Superintendent of Documents, U. S. Government Printing Office 

Washington 25, D. C. - Price $1.00 (paper cover)
CONTENTS

Page

Abstract_______________________________________________________ 155

Introduction- __ ____________________-_____________-___-,____-.-__-_ 157

Scope and purpose of the investigation________________________ 157

Acknowledgments___ _ _________'_________--________-_--__-____ 157

Historical sketch____________________________________________ 158

Geographic sketch.____________________________________________ 158

Climate_______________._____________________ 159

Physiography___________________________________________________ 162

General features.______-________-_-______---________-_----_-__- 162

Physiographic districts______________________________________ 162

Central highlands__________________________________ 163

Western plateau__-_________-_________-_________-_-_-_____- 168

Eastern uplands..__________-_-___-_-_----__________--____- 169

Northern highlands________________________________________ 169

Coastal plain___________________________________________ 169

Geology__________________________________________ 170

Sequence and general features of the rocks._______________________ 170

Summary of the geologic history______________.__________________ 170

Physical character and water-bearing properties of the strata________ 173

Quaternary system______________________________________ 173-

Recent series_______________________________________ 173

Beach and estuarine deposits______________________ 173

Landslides, talus, and alluvial fans_________________ 174

Younger alluvium_________________________________ 175

Younger Quaternary lavas and pyroclastic deposits _____ 176

Pleistocene series______________________________________ 177

Older alluvium__________________________________ 177

Older Quaternary lavas and pyroclastic deposits ________ 178

Lake beds____._______________________ 179

Tertiary system________________________________________ 181

Late Tertiary (?) pyroclastic deposits and lavas_________ 181

Early (?) Tertiary volcanic rocks and related sedimentary

rocks__________.______________________ 183

Cretaceous and Jurassic systems___________________________ 185

Lower Cretaceous and Upper Jurassic series_____________ 185

Metapdn formation________________________________ 185

Ground water _____________________________________________________ 18&

Introduction._________________________________________________ 186-

Ground-water resources by departments________-___---___---_____ 187

Departamento de Ahuachapdn_______________________________ 187

General features.._____________________________________ 187

Ground-water conditions___.______._____________________ 188

Local supplies_________________________________________ 189

Ahuachapdn __ ___________________________________ 1891

Atiquizaya___ _ __________________________________ 189-

in
IV CONTENTS

Ground Water Continued

Ground-water resources by departments Continued Page

Departamento de Cabanas________________________________ 190

General features_____________________________________ 190

Local supplies_________________________________________ 191

Sensuntepeque ____________________________________ 191

Departamento de Chalatenango.____________________________ 191

Departamento de Cuscatl£n________________________________ 192

General features_______________________________________ 192

Ground-water conditions._______________________________ 193

Local supplies____________'_____________________________ 194

Cojutepeque ______________________________________ 194

El Carmen______________________________________ 194

San Rafael Cedros_______________________.______ T ___ 194

Departamento de La Libertad_____________________________ 195,

General features_--_----_------___---_____________--_-_ 195

Ground-water conditions.______________________________ 195

Local supplies-________-___--_______-____-__-______--_. 197

Antiguo Cuscatl£n_________________________________ 197

Quezaltepeque_ ________-_____-___-_---_________-_- 197

Nueva San Salvador (Santa Tecla)__________________ 197

Departamento de La Paz______-_____________________-______ 198

General features..__________________________'___________ 198(

Ground-water conditions.______________________________ 199

Local supplies...._____________________________________ 200

Zacatecoluca_ _____________________________________ 200

Departamento de La Uni6n_________________________________ 200

General features__-______------___-____----_--_-------- 200

Ground-water conditions. ______________________________ 201

Local supplies__________---_---__-_____----_---___-_-_- 201

Santa Rosa____-__--------_____-__-------_-------- 201

Departamento de Morazan_________________________________ 202

General features-______________________________________ 202

Ground-water conditions_______________________________ 202

Local supplies_______----------__---------------_---_-_ 203

Jocoro_ _ __________-__----__--_-_-_-_-_----__---_- 203

San Francisco._________-____I_______________-___-_ 203

Departamento de San Miguel_-__---___-_-__---_-__--__---_- 203

General features__________-----_____--_------_--------- 203

Ground-water conditions.______________________________ 204

Departamento de San Salvador___________________________.__ 204

General features____------_--------_---_---___--------- 204

Ground-water conditions.______________________________ 205

Local supplies_________________________________________ 206

San Salvador._______________________________ 206

Mejicanos ________________________________________ 207

Villa Delgado__-------------------------_-------- 208

San Martin____________________________________ 208

Tonacatepeque_ ___________________________________ 209

Departamento de San Vicente_____________________________ 209

General features.______________________________________ 209

Ground-water conditions.______________________________ 209

Local supplies_________-___^__-___-___-_-___--_-------- 211

Guadalupe_______-____-___________-____-_-----__-_ 211

San Vicente___.____________________ 212
CONTENTS

Ground water Continued

Ground-water resources by departments Continued page

Departamento de Santa Ana ___ ___________________________ 212

General features. ______________________________________ 212

Ground-water conditions_____________________________._ 213

Departamento de Sonsonate_________________--_____________ 215

General features______________________-________________ 215

Ground-water conditions. ______________________________ 215

Local supplies_____-_-__--______-____-__-_--_-____---_- 216

Armenia _ _______________________________________ 216

San Julian _________ . _______ _ _________ __ 217

Departamento de Usulatdn__________________---____-__--__- 217

General features________________________-_________----_ 217

Ground-water conditions__________________-_____--__-__ 217

Local supplies._______--___________________-______-_--__ 220

Alegrfa_-__-_-----_-_-___---_--__------___-------- 220

Jucuapa_ _________________________________________ 220

Usulatan. ____________________________ ____ ___ _ 221

Index _ _ __ _____ _____ ____________ ________ ___ _____ --._ 223

ILLUSTRATIONS

Page

PLATE 3. Map of the Republic of El Salvador, Central America..-- In pocket 

FIGURE 7. Index map of Central America showing the location of the

Republic of El Salvador.._____________________________ 159

GROUND-WATER RESOURCES OF THE REPUBLIC 

OF EL SALVADOR, CENTRAL AMERICA

By A. N. SATEB and G. C. TAYLOR, JR.

ABSTRACT

This report is based on an investigation by the writers of the U. S. Geological 

Survey assigned to the Institute of Inter-American Affairs to determine the 

ground-water resources of El Salvador, especially with reference to the development of ground water for public water supplies and for domestic use. The 

field work on the investigation was carried on from June 1943 through February 1944. During this period, studies were made of the water-supply problems of some 30 towns and cities in the republic.

El Salvador, smallest of the five Central American Republics, covers an area 

of about 13,176 square miles. The climate of the country is the savanna typical 

of the subequatorial belt of the tropics. There are two seasons, a wet season 

from June to October, inclusive, and a dry season during the low-sun period. 

The average annual rainfall over the country as a whole is about 75 inches, most 

of which occurs in the wet season.

Much of the western and central part of El Salvador is an elevated plateau 

ranging from 1,000 to 2,000 feet above sea level. The eastern part of the country 

Is largely a hilly upland ranging from 500 to 1,500 feet above sea level. The 

plateau and upland are moderately dissected by numerous canyons and narrow 

valleys separated by broad sloping interfluves. Surmounting the plateau and 

upland are five groups of volcanic peaks which form a discontinuous highland 

that traverses the country from east to west. The summits of this highland 

rise from 5,000 to 8,000 feet above sea level. Bordering the shore line is a 

narrow coastal plain that rises inland to an elevation of about 500 feet.

In El Salvador, nonmarine strata of the Tertiary and Quaternary systems 

rest on igneous and sedimentary rocks of Cretaceous and greater age. Apparently the oldest rocks in the republic belong to the Metap&n formation of 

late Jurassic and early Cretaceous age. The formation includes interbedded 

sandstone, shale, conglomerate, marl, and limestone with occasional strata of 

tuff and breccia. Locally the rocks of the Metapan formation are intruded by 

stocks and dikes of granite, granodiorite, and diorite. These intrusive rocks 

may be of late Cretaceous or early Tertiary age. The strata of the Tertiary 

system include extrusive basalt, andesite, and some intermediate and acidic 

extrusive rocks; volcanic ejectamenta that range from scoria to compact tuff, 

agglomerates, and breccia; and detrital sediments of alluvial and lacustrine 

origin. The strata of the three classes are interlaminated and interfingered, 

and they grade laterally into one another in a complex fashion. The rocks 

of the Quaternary system include basic lavas and pyroclastics erupted from 

central vents, and 'alluvial, lacustrine, and beach sediments deposited in the 

larger valleys and basins, and along the seaward margin of the costal plain.

155
156 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

The rocks of the Metapan formation of late Jurassic and early Cretaceous 

age crop out in the northern highlands of the Departamento de Santa Ana and 

the Departamento de Chalatenango. These rocks are not generally very permeable but may yield small supplies of good water to wells and springs from 

fractures or solution passages. The Upper Cretaceous (?) intrusive rocks that 

cut the Metapan formation are not generally permeable but fractures and 

weathered zones may yield small supplies of water to wells and springs.

Strata of early (?) Tertiary age crop out chiefly in the northern highlands 

and the eastern upland. The rooks include weathered basalt and felsitic lavas 

with intercalated pyroclastic rocks and detrital sediments. These rocks generally have low permeability owing to cementation and induration of the 

sedimentary beds and alteration of the volcanic materials. Fractures may 

yield small supplies to springs, and locally fragmental and scoriaceous zones 

in the lavas yield moderate to large supplies of water to wells and springs.

Rocks of late Tertiary (?) age underlie younger volcanic rocks and detrital 

materials of the central highland, the western plateau, and the coastal plain. 

The rocks are chiefly andesitic agglomerates, breccias, and tuffs intercalated 

with basaltic and andesitic lava flows. The fragmental and scoriaceous facies 

of the andesitic and basaltic lava flows, where present in the zone of saturation, 

Shield moderate to large supplies of water to wells and springs.

The Pleistocene series of the Quaternary system include lake beds, the older 

Quaternary lavas and pyroclastics, and the older alluvium.. The lake beds 

include water-laid clay, silt, and sand derived from pyroclastic ash, pumice, 

and cinders, and deposited in lava-dammed basins. The sandy and cindery beds 

yield moderate supplies of water to wells and springs, but the clayey beds are 

largely impermeable. The scoriaceous and fragmental facies of the older 

Quaternary lavas are permeable and yield moderate to large supplies of water 

to many wells and springs in the republic. Among the older Quaternary pyroclastics are pumice and cinder beds which are ordinarily productive water-bearing horizons when present in the zone of saturation. The beds of volcanic ash 

are generally impermeable but locally yield small supplies to wells and springs. 

The older alluvium, where present in the zone of saturation, yields moderate 

supplies of water to wells and springs.

The Recent series of the Quaternary system includes younger Quaternary lavas 

and pyroclastics, younger alluvium, landslides, talus, and alluvial fans, and 

beach and estuarine deposits. The young Quaternary lavas and pyroclastics 

are generally above the regional water table. However, locally perched bodies 

of ground water occur in these rocks that yield small supplies to shallow wells 

and temporary springs. The younger alluvium contains considerable water at 

shallow depth in the lower stream valleys. The landslide and talus masses, 

and the alluvial fans are generally above the regional water table. Along the 

coast dune sand, where present in the zone of saturation above sea level, yields 

small supplies of potable water to shallow dug wells.

Practically all the cities and towns in El Salvador obtain water supplies for 

public -and domestic use from wells and springs. The majority of the supplies 

are obtained by gravity through pipelines from developed springs. A few towns 

and cities, because of their topographic position, obtain water from pumping 

stations located at-springs lying at lower elevation. Because of improved economic conditions and the efficiency of modern pumps, wells are being used to 

an increasing degree as sources of public water supplies in the Republic. This 

report describes the water supplies of some 25 towns and cities in the Republic.
ACKNOWLEDGMENTS 157 

INTRODUCTION 

SCOPE AND PUBPOSE OF THE INVESTIGATION

This report is based on an investigation made by geologists of the 

Geological Survey, United States Department of the Interior, assigned to the Institute of Inter-American Affairs. The writers, of the 

Ground Water Branch of the Survey, were assigned to the Institute's field party in El Salvador to study critical problems of water 

supply as a part of the program of the Health and Sanitation Division 

in cooperation with the Salvadorean Government. Dr. Sayre spent 

31X3 months in El Salvador, from June until September 1943, and Mr. 

Taylor spent 7 months, from July 1943 until February 1944.

During the course of the field,work, geologic and hydrologic studies 

were made of the water-supply problems of about 30 towns and 

cities in the republic. Individual reports have been prepared in both 

English and Spanish for each of the localities visited. They describe 

the geologic, hydrologic, sanitary, and economic features of existing 

and potential water supplies and contain recommendations for their 

development and improvement. These reports, in manuscript form, 

are available for consultation in the files of the Health and Sanitation 

Division field office in San Salvador, Central America, and also in the 

files of the Ground Water Division, U. S. Geological Survey, in Washington, D. C. The places visited are shown in plate 3.

Geologic and hydrologic studies were also made along the Pan 

American Highway in the 180-mile stretch from the Guatemala border to the -border of Honduras. About 50 sites were selected for the 

development of springs or the construction of wells as roadside watering places along the highway, for travelers or stock.

The present report summarizes the general geologic and groundwater features of El Salvador, as based on field observations made in 

the course of more detailed municipal water-supply studies.

ACKNOWLEDGMENTS

The need for ground-water studies in El Salvador was first recognized by Lt. Col. H. W. Van Hovenburg, chief of the field party for 

the Health and Sanitation Division of the Institute, and Dr, Victor 

Arnoldo Sutter, Director of the Salvadorean Sanitation Service. It 

was through Colonel Van Hovenburg's initial request that the writers 

were assigned to the project. Dr. Sayre planned the field program 

and directed the first phases of the work. After Dr. Sayre's return 

to the United States, the field program was carried on and completed 

by Mr. Taylor with the capable assistance of Sres. Mario Pacheco 

and Carlos Aleman, engineers assigned to the field group by the 

government of El Salvador.

930754 51 2
158 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

HISTORICAL SKETCH

The j&rst inhabitants of the region now called El Salvador, according to reports, were Indians of the Nahoa group, who migrated from 

Mexico. Later the Pipil Indians entered the country and settled in 

the coastal area from the Guatemala frontier to the mouth of the 

Rio Lempa. At about the same time Indians of the Ohontal group 

settled in the eastern part of the country from the Golfo de Fonseca 

to the Lempa valley.

Under the leadership of Don Pedro de Alvarado, the Spaniards 

j&rst entered Salvadorean territory in May 1524, founding at that time 

the city of San Salvador. The country remained under Spanish rule 

until September 21, 1821, when, as a part of the Central American 

Federation, El Salvador declared its* independence from Spain. In 

January 1822, an attempt was made by Emperor Iturbide to incorporate the Central American States in the Mexican union, but the 

proposed annexation was successfully resisted by armed force. In 

July 1823 the Congress of the Central American Federation proclaimed that the States of the isthmus were independent of Spain, 

Mexico, and any other country of the old or new world.

Because of dissatisfaction with the organization of the Federation, 

the State Legislative Congress declared on January 30, 1841, that El 

Salvador would resume its sovereignty and would call itself the Republic of El Salvador in Central America. It declared, moreover, 

that its withdrawal was only temporary, as it ultimately desired the 

reestablishment of a great, firmly founded Central American nation.

GEOGRAPHIC SKETCH

The Republic of El Salvador lies on the isthmus of Central America 

between 13°08' and 14°24' north latitude and 87°39' and 90°08' west 

longitude. San Salvador, capital of the republic, is approximately 

1,100 miles south of New Orleans, La., in the United States.

El Salvador, smallest of the five Central American Republics, covers 

about 13,176 square miles. The country has the rough outline of a 

rectangle 160 miles long from east to west and 60 miles wide from 

north to south. It is bordered on the north by the Republic of 

Honduras, on the west by the Republic of Guatemala, on the south 

by the Pacific Ocean, and on the east by a part of Honduras and the 

Golfo de Fonseca. (See fig. 7.)

For governmental administration the country is divided into 14 

departments and 259 municipalities. The largest city and the capital 

of the republic is San Salvador (population 97,161), located in the 

west-central part of the country. Other principal cities are Santa 

Ana (population 77,136) in the extreme west and San Miguel (population 41,109) in the eastern part of the country. La Union on the
CLIMATE 159

C A R I B B E A

FIGURE 7. Index map of Central America showing the location of the Bepublic of

El Salvador.

Golfo de Fonseca is the chief seaport, but considerable commerce 

passes through the ports of La Libertad and Acajutla.

The total population of El Salvador is 1,787,930, or an average of 

135.7 inhabitants per square mile. Some 90 percent of the inhabitants are mestizos of mixed Spanish and Indian origin. There are 

no uncivilized Indians in the country.

CLIMATE

El Salvador, located 13° to 14° north of the equator, has a climate 

typical of the warm tropical regions of the world. The seasons are 

marked by variations in rainfall rather than by changes in temperature. Temperature and rainfall vary chiefly with altitude. The 

lowlands are hot and sultry but are generally drier than the moist, 

more temperate uplands of the interior.

As is characteristic of the subequatorial belt of the tropics, there 

are only two seasons, a wet period and a dry period. The rainy season 

lasts from June through October. May and November are marked 

respectively by increasing and decreasing rainfall, at the beginning 

and the end of the rainy season.

During the wet season there is frequent, almost daily rainfall. The 

rains of June and July come as short, intense showers with thunder
160 GROUND-WATER RESOURCES OF E,L SALVADOR, CENTRAL AMERICA

and lightning. In August and September the storms are often prolonged in "temporals," during which rain may fall continuously for 

3 or 4 days. These storms are generally regional in contrast with the 

local thunder showers earlier in the season.

During the dry season, winds from the north are the dominant factor controlling the weather. These winds reach the Caribbean coast 

of Honduras laden with moisture. Condensation and precipitation of 

the moisture load take place when the winds pass over the high mountain ridges of southern Honduras. Because most of the precipitation 

occurs on the north slopes of the mountains, the winds reaching El Salvador are generally dry and only infrequently produce rain.

In general, the rainfall in El Salvador increases with altitude, but 

there are many local differences owing to the alinement of the mountains with respect to wind direction. The average annual rainfall 

over the country as a whole is about 75 inches. Areas with elevations 

of more than 3,000 feet above sea level, particularly in the vicinity of 

the high volcanic peaks, receive 85 to 100 inches of rain annually. 

The driest section is in the eastern part of the country, in the departments of Morazan and La Union, where the annual rainfall ranges 

from about 40 to 50 inches a year.

The following table shows the monthly, yearly, and average rainfall from 1912 to 1936 as based on data of the National Meteorological 

Observatory at San Salvador. This station gives a representative 

picture of the distribution of the rainfall in the country as a whole.
Rainfall, in inches, at San Salvador, El Salvador, Central Am

[Based on data of the National Meteorological Observatory

Year

1Q1 Q

1916.. _ .... ___ -

1917-. - _ _ -- __ 

1919... _ __

1920

1QOO

1925--- 

1926-. 

1929.- --

inon

1931-- 

1932.. . 

1934--- - 

1935-.--- 

1 QTfi

January

0

0

ft QO

.30

1.16

0

dn

.50

.06

00

.07

0

.79

.06

0

.12

0

.01

0

.51

.26

0

.05

.20

February

0

C

0.18

0

0

.02

.57

0

0

.92

0

.93

.09

0

.22

.13

0

.28

.72

0

.95

0

.53

.28

March

0

0 97

0

.02

0

.61

3.12

0

.01

2.08

1.38

.18

.22

0

.01

0

.05

.47.

0

.77

0

.29

.13

.38

April

.33

3.86

.73

2.19

2.12

.40

11.29

2.20

0

2.91

.18

2.44

4.44

1.17

.36

0

.88

1.67

2.25

.08

.77

.16

1.77

May

4.11

5.66

9.47

4.47

2.68

12.83

3.44

7.38

5.95

7.01

7.62

8.15

14.95

8.10

7.78

7 60

7.86

8.17

11.12

12.86

6.18

7.93

June

7.81

9 

on

13.25

12.27

11.72

14.00

13.79

11.44

10.65

16.21

17.60

15.01

13.38

12.02

16.71

12.86

12.13

12.28

11.32

20.28

14.10

15.65

22.49

10.19

24.25

14.03

July

14.49

9.00

9.36

14.58

7.63

15.21

12.42

13.81

9.93

10.40

6.11

11.55

15.68

16.86

12.44

18.94

 17.90

13.48

6. 06

10.73

12.60

11.92

8.24

6.77

11.45

11.90

A
\ 

162 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

PHYSIOGRAPHY

GENERAL FEATURES

El Salvador, though small in area, is a region of considerable physiographic diversity. Much of the western and central part of the 

country is an elevated plateau of moderate relief ranging from 1,000 

to 2,000 feet above sea level. Along its margins the plateau has been 

dissected by numerous deep canyons and narrow valleys separated by 

broad sloping interfluves. The eastern part of the country is chiefly 

low hilly uplands with well-integrated stream valleys, and it ranges 

from about 500 to 1,500 feet above sea level.

Surmounting the western plateau and the eastern uplands are five 

groups of volcanic peaks which form a discontinuous mountainous 

highland that traverses the country from east to west. The basal slopes 

of the volcanic groups range from 2,000 to 3,000 feet above sea level, 

Ibut the summits rise from 5,000 to 8,000 feet.

Along the northern frontier of El Salvador the outlying ridges of 

the Central American Cordillera extend from southern Honduras into 

the northern parts of the departments of Santa Ana, San Miguel, 

Morazan, and western Chalatenango. The crests of many of these 

ridges are more than 3,000 feet above sea level.

Bordering the shore line is a coastal plain which rises inland to an 

elevation of about 500 feet. From the Guatemala border to the valley 

of the lower Rio Lempa the plain is generally narrow and rises sharply 

to the interior plateau within a few miles of the coast. East of the 

Rio Lempa the coagtal plain merges almost imperceptibly with the 

low hilly uplands of the eastern interior of the country.

The Rio Lempa, which rises in the highlands of Guatemala and 

Honduras, enters El Salvador near the northwestern corner of the 

country. For the first 35 miles of its course in El Salvador it flows 

southwest through narrow canyons and valleys. It then turns abruptly 

eastward and flows on a much lower gradient for about 70 miles, first 

through the lowland plains of southern Chalatenango and northern 

San Salvador and then through a somewhat narrower valley, where 

the river forms the Honduras frontier. Near Sensuntepeque the river 

bends to the south and then follows a southwesterly course for about 

60 miles .to the sea. In the upper part of this last stretch the river 

occupies a relatively narrow valley, which gradually widens to 3 or 4 

miles where the stream flows out on the coastal plain about 20 miles 

above its mouth. The general relations of topographic features and 

drainage in the republic are shown in plate 3.

PHYSIOGRAPHIC DISTRICTS

The land forms that make up the landscape of El Salvador may be 

divided roughly into five physiographic districts: The central high-
PHYSIOGRAPHY 163

lands, the western plateau, the eastern upland, the northern highlands^ 

and the coastal plain.

CENTRAL HIGHLANDS

The central highlands include most of the areas above 2,000 feet that 

cross the middle of the country in an irregular, discontinuous band, as 

shown in plate 3. The highlands include five principal groups of clustered volcanic peaks with their associated and overlapping eruptive 

fields. Most of the land forms in the highlands are relatively young 

and have been built up by volcanic processes that are still active. The 

forms include lava and tuff cones, cinder cones, lava and tuff fields, 

and other initial volcanic surfaces with associated explosion craters 

and collapse calderas. The five volcanic highland groups from west 

to east are Apaneca-Santa Ana, San Salvador, Cojutepeque, San Vicente, and Tecapa-San Miguel.

The Apaneca-Santa Ana highland is distinguished from the other 

volcanic clusters of the central highlands by the nearness of the eruptive centers to one another and their linear, chainlike arrangement.1 

There are numerous eruptive centers in the group, of which only the 

larger features are described here. The principal volcanoes of the 

group from west to east, with their elevations above sea level, are: 

Volcan de Apaneca (6,015 feet), Lagunita (5,788 feet), Laguna Verde 

(5,930 feet), Cerro San Juan (6,035 feet), Aguila (6,322 feet), Laguna 

de Rana (6,540 feet), Naranjo (6,448 feet), Santa Ana (7,751 feet), 

and Izalco (6,126 feet).

The Volean de Apaneca, about 5 miles southeast of Ahuachapan, 

apparently is a deeply eroded volcano of basaltic lava and pyroclastic 

rocks without vestiges of a crater. The volcanoes of Lagunita and 

Laguna Verde are about 4*/2 and 5 miles, respectively, east-southeast 

of Ahuachapan. Each contains a well-developed summit crater enclosing a small crater lake. East of Laguna Verde is Cerro San Juan, 

which appears to be an eroded volcano with several remnant crests. 

Along the north flank of the mountain are six or more active groups 

of gas fumaroles, steam vents, hot springs, and mud geysers. The 

temperatures and discharges of many of the hot springs are reported 

to fluctuate markedly with the seasons. The greatest discharges and 

lowest temperatures occur in the wet season when ground-water storage, depleted during the dry season, is replenished by meteoric water 

from rain. Apparently the waters of the hot springs are mixtures of 

the cool, normal meteoric ground water and hot juvenile water from 

deep-seated sources associated with volcanism. Mixing of the two 

types of water probably takes place at shallow depth in the vicinity 

of the hot-spring orifices. The temperature at which the spring water

1 Sapper, Karl T., Los volcanes de la America Central: Studien liber Amerika und 

«panien, no. 1, p. 38, Halle (Saale), Max Niemeyer, 1925.
164 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

emerges from the orifices depends principally on the relative proportions of the two waters in the mixture. In the wet season the lowest 

temperatures occur because of the relatively greater proportion of 

cool meteoric ground water in the mixture. At the same time the 

spring flow is greater because of excess ground-water overflow from 

abundant rain. In a number of instances, orifices which yield hot 

water in the wet season become steam vents in the dry season. According to Dollfus and de Montserrat,2 many of the hot springs and 

steam vents also discharge sulfur dioxide, hydrogen sulfide, carbon 

dioxide, and nitrogen. In the vicinity of the vents and spring orifices, 

these gases in conjunction with steam and thermal waters have formed 

primary deposits and alteration products through action on the adjacent country rock. Renson and Puente,3 who analyzed these products, concluded that they were chiefly sulfates of aluminum, iron, 

calcium, and magnesium, but mixed carbonate, silicate, and sulfate 

of calcium, iron oxide, and aluminum silicate were also noted.

East of Cerro San Juan are the volcanoes of Aguila and Laguna 

de Rana. The volcano of Laguna de Rana has a small summit crater 

enclosing a shallow marshy lake. A short distance to the south is the 

isolated volcanic cone of Naranjo, with an oval-shaped crater 450 

feet long and about 65 feet deep. The rocks in the vicinity of the 

crater are largely volcanic cinders.4

The largest volcano in the western group is Volcan de Santa AnaT 

which is also the highest point in El Salvador. According to Sapper,5 

there is some evidence of a progressive shifting of the center of eruption toward the east. There are two semicircular remnants of old 

crater walls west of the principal crater, which is about 3,100 feet 

long and 2,300 feet wide. Farther to the southeast is a still younger 

but deep crater. According to historical records, the volcano was 

active several times between 1520 and 1570. There was then a period 

of quiescence of more than 300 years until the eruptions of 1874 and 

1880 which covered the town of Sonsonate with a blanket of ashes 

4 inches deep. The rocks composing the volcano are chiefly aiidesitic 

and basaltic lava flows with associated pyroclastics..

To the east of Volcan de Santa Ana is the large caldera sink of 

Coatepeque. This closed depression appears to have been formed by 

explosion and later enlarged by collapse. The lake that fills the 

bottom of the depression is almost round and is about 3% miles wide 

and 400 feet deep. The walls of the caldera rise steeply on all sides 

350 to 650 feet above the lake surface.

On the southern slope of Volcan de Santa Ana and about 8 miles

2 Sapper, Karl T., op. cit., p. 40. 1925.

3 Idem. 

* Idem. 

5 Idem.
PHYSIOGRAPHY 165

northeast of Sonsonate is the Volcan de Izalco, which is one of the 

few volcanoes known to have been formed within historic times. According to Larde,6 the upbuilding of the volcano apparently began 

with the eruption in March 1722 of lava flows and ash from a satellite 

vent on the slope of Volcan de Santa Ana. There were then minor 

eruptions from time to time until February 1770, when the first major 

activity occurred. At this time a large flow of lava poured out of 

the vent and scoria, rock fragments, and ash were ejected explosively 

and were accompanied by strong earthquakes in the neighboring region. From this time until 1856 the volcano was intermittently active 

for periods of several months to a few years, alternating its explosions 

of fragmental materials with the effusion of lava. Notable activity 

occurred in 1783, 1798, 1803, 1825, and 1838. From 1856 until the 

present the activity and frequency of eruptions has gradually increased. At present Izalco is possibly the most active volcano in 

Central America. Eruptions of ash, cinders, and volcanic bombs 

commonly occur at intervals of 15 to 20 minutes. From its beginning 

as a satellite vent, the cone has been gradually built up to a height 

of 2,600 feet above its base through the accumulation of fragmental 

products and basaltic lava flows.

The San Salvador highland is separated from the Apaneca-Santa 

Ana highland by the 15-mile gap of the Zapotitan basin. The chief 

physiographic features of the highland are Volcan de San Salvador 

with its satellite cones and eruptive centers, the great sink of Laguna 

de Ilopango, and the high east-west ridge locally known as the Cadena 

Costera (Coast Range).

Volcan de San Salvador (elevation 6,337 feet) is about 7 miles northwest of the city of San Salvador. Evidently it has been long exposed 

to erosion. Deep canyons score its flanks and drain radially from 

its crest, which has no apparent vestiges of a summit crater. Southwest of Volcan de San Salvador, and separated from it by a topographic saddle, is the Boqueron or volcano of Quezaltepeque (elevation 6,133 feet), which is evidently younger. A huge crater about 

1,500 feet deep, about 4,000 feet in diameter, and almost circular in 

outline lies in the upper part of the volcano. At the time of the 

writers' visit, in September 1943, the volcano was inactive, but a small 

cinder cone built on the floor of the crater was observed. According 

to Sapper,7 the cone was formed during the eruption of June 1917, 

immediately following the disappearance of a crater lake which had 

boiled away as a consequence of the eruption. The cone, which rose 

about 100 to 130 feet above the floor of the crater, resulted from the

6 Larde, Jorge, Geologia general de Centre-America y especial de El Salvador : Imprenta 

Nacional, San Salvador, p. 31, 1924.

7 Op. cit., p. 53.

930754 51 3
166 GROUND-WATER RESOURCES OF IKL SALVADOR, CENTRAL AMERICA

accumulation of ash and cinders which accompanied the explosion 

cf steam and other gases during the eruption.

About 6 miles west of San Salvador is the western edge of the 

Ilopango volcanic sink, which lies near the eastern end of the San 

Salvador highland. Laguna de Ilopango occupies the lowest part of 

this sink. In places the lake is more than 650 feet deep, and it is about 

7 miles long from east to west and 5 miles wide from north to south. 

Its water surface is about 1,565 feet above sea level. The depression 

is bordered on all sides by steep, precipitous slopes which rise from 

800 to 1,000 feet above the lake surface. The bordering slopes have 

been deeply dissected by short canyons of streams draining centripetally toward the lake. The outlet of the lake, at the eastern end, drains 

into the Rio Jiboa by way of the canyon of the Desague. The canyon 

apparently wa's formed by the headward erosion of a tributary of 

the Rio Jiboa, which cut back through the soft tuff and ash forming 

the rim of the depression. The Ilopango depression appears to have 

been formed in Pleistocene or Recent time by explosions at one or 

more adjacent vents, with subsequent enlargement of the sunken area 

by collapse and integration of the adjoining craters previously 

formed.

The Cadena Costera (Coast Range) of El Salvador is a high ridge 

trending in an east-west direction for 40 miles, extending from about 

10 miles southwest of Laguna de Zapotitan to the eastern end of 

Laguna de Ilopango. (See pi. 3.) Through much of its length the 

crest of the ridge ranges from about 2,500 to 3,500 feet above sea 

level. The ridge is bordered on the north by an 800-foot escarpment 

dissected by numerous short ravines draining northward to the Rio 

Lempa and Laguna de Ilopango. The southern flank slopes more 

gradually to the coast, though it too is dissected by many deep parallel 

canyons of streams draining southward to the sea.

Directly east of Laguna de Ilopango, and separated from the San 

Salvador highland by a low area only a few miles wide, is the 

Cojutepeque highland. It is a moderately dissected hilly region with 

elevations ranging from 2,500 to about 3,000 feet above sea level. The 

only pronounced elevation in the region is the Volcan de Cojutepeque 

at the southern outskirts of the city of that name. The crest of the 

volcano rises about 3,320 feet above sea level and 425 feet above the 

surrounding country, The summit crater is about 700 feet in diameter. Its eastern wall has been destroyed by erosion.

The San Vicente highland includes the area above 2,500 feet around 

the Volcan Chichontepec southwest of the city of San Vicente (see 

pi. 3). It is separated from the Cojutepeque highland on the north 

and west by the valleys of the Rio Jiboa and Rio Acahuapa. Volcan 

Chichontepec (elevation 7,065 feet above sea level) has two peaks.
PHYSIOGRAPHY 167

According to Sapper,8 the eastern peak has a well-preserved crater, 

and the western peak has a crater which has been breached toward the 

east. There has been no activity at either of the craters in historic 

times. Both of the summit areas are well-covered with a heavy forest. 

On the northwest slope of the volcano, at an elevation of about 2,665 

feet, are the fumaroles of San Vicente. Dolfus and de Monteserrat 9 

suggest that the gases emitted from the vents are perhaps 95 percent 

water vapor with small amounts of sulfur dioxide, hydrogen sulfide, 

carbon dioxide, nitrogen, and oxygen. In the same vicinity there are 

also several small hot springs and a mud volcano about 30 inches high.

The Tecapa-San Miguel highland lies in the east-central part of the 

republic and is separated from the San Vicente highland by the 15- 

mile gap of the lower Rio Lempa valley. Five volcanoes with their 

overlapping eruptive fields and several minor peaks make up the highland. The principal volcanoes, and their elevations above sea level 

are: Volcan de Tecapa (5,210 feet), Volcan Usulatan (4,712 feet) y 

Cerro del Tigre (5,388 feet), Volcan Chinameca (4,555 feet), and 

Volcan de San Miguel (6,849 feet). Volcan de Tecapa lies immediately south of the town of Alegria. The summit is west-northwest of 

the crater, in a somewhat eccentric position. The crater is approximately 2,500 feet in diameter, and its floor is occupied by a lake about 

1,150 feet long and 850 feet wide. The crater walls, composed chiefly 

of andesite lava flows, rise 1,150 feet above the lake surface at the 

highest point. On the west side of the crater, where erosion has 

notched the wall, the rim is only about 75 feet above the lake surface. 

Directly southwest of Jucuapa is Cerro del Tigre, an enlongate volcanic 

mass whose crest and flanks have been considerably dissected and reduced by stream action. Volcan de Usulatan, which is about 7 miles 

north bf the city of that name, has vestiges of two large summit craters 

which closely adjoin each other. However, both have been partly 

destroyed by erosion and are open to the east. Sapper 10 is of the 

opinion, from their state of preservation, that Cerro del Tigre and 

Volcan de Usulatan are older volcanoes than Volcan Tecapa. None 

of these has been active in historic times.

Volcan Chinameca, south of the city of Chinameca, is notable for 

the large size of its summit crater, which is 6,500 feet in diameter. 

The crater walls, composed of andesite lava flows, rise 1,500 feet above 

the crater floor at the highest point, but at one point where erosion 

has breached the wall the rim is only 300 feet above the floor.

Volcan de San Miguel is perhaps the most perfectly formed volcanic cone in El Salvador. On all sides its slopes rise abruptly from 

the surrounding lowlands. It is only on the northwest that its basal

8 Sapper, Karl T., op. cit., p. 56.

9 Idem.

10 Op. cit., p. 57.
168 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

slope converges with a spur ridge from Volcan Chinameca at an elevation of about 3,500 feet. Its slopes are only slightly dissected by 

small gullies which drain radially away from the crater rim. Lava 

fields, covering extensive areas around the base, were formed by eruptions from small aventitious cones. The summit crater of the volcano 

is approximately 2,500 feet in diameter, and its infacing walls are 

composed of volcanic scoria, breccia, and lava flows. At the time of 

the junior author's visit in December 1943, a vertical-walled crater 

pit about 800 feet deep and 1,600 feet in diameter existed near the 

east-northeast wall of the summit crater. Surrounding the pit was 

a flat, narrow bench of loose cinders and scoria, strewn with volcanic 

bombs and rock fragments. This bench, which represents a former 

level of the crater floor, is being destroyed by landslides which take 

place along fissures concentric around the lip of the pit. A small 

secondary cinder cone which had been built on the bench level is now 

practically destroyed by the landslides. Several large f umaroles were 

observed at the bottom and in the lower walls of the pit. They fill 

the pit at periodic intervals with white clouds of steam, sulfur dioxide, 

and hydrogen chloride. Recorded eruptions of basaltic lava from 

satellite vents on the flanks of the volcano occurred in 1T62,1787,1811, 

1819, 1844, 1848, and 1867. Ash and cinder eruptions occurred at the 

summit crater in 1699, 1769,1798, 1845-47, 1854-57, and 1879.

WESTERN PLATEAU

The western plateau of El Salvador includes most of the area between 500 and 2,500 feet above sea level west of the Eio Lempa (see 

pi. 3). It includes intermontane upland valleys, basins, and plains 

lying around and between the central and northern highland areas. 

Several isolated volcanoes north of the central highland are also included in this district. Most of the land forms in the western plateau 

are older than those in the central highlands and have been constructed 

by volcanic processes now inactive. Erosion has reduced original constructional forms such as volcanic cones, lava flows, and ash beds to 

undulating plains and valleys with occasional isolated buttes and 

hills.

West of Santa Ana is the plain of Candelaria (llano de Candelaria), 

which slopes northwestward from the base of the Apaneca-Santa Ana 

highland to the Eio de Paz. East of Lago de Giiija is a moderately 

dissected upland which slopes eastward to the Rio Lempa. Lying 

between the Apaneca-Santa Ana and San Salvador highlands is the 

Zapotitan basin (valle de Zapotitan), which drains northward to the 

Rio Lempa by way of the Rio Sucio. This basin is contiguous on 

the northeast with the plain of Aguilares (llano de Aguilares), which 

slopes northward to the Rio Lempa from the base of the San Salvador 

highland. Rising above this plain near the junction of the Rio
PHYSIOGRAPHY 169

Acelhuate and the Rio Lempa is the volcano of Guazapa (elevation 

4,582 feet). (See pi. 3.) According to Sapper,11 erosion has destroyed 

the original summit crater, and nothing remains but the radiating 

network of the principal feeder dikes.

North of the Rio Lempa the plains of Chalatenango (llano de 

Chalatenango) slope southward to the river from the dissected highland and plateau of the northern and western parts of Departamento 

de Chalatenango.

EASTERN UPLANDS

The eastern uplands include most of .the areas east of the Rio Lempa 

ranging from about 500 to 1,500 feet above sea level. The land forms 

are apparently older than neighboring parts of the central highlands. 

Much of the republic east of San Miguel is composed of subdued, 

rounded hills of moderate relief, dissected by broad, well-integrated 

stream valleys. This topography has been developed from older volcanic rocks whose original constructional forms have been largely 

destroyed by erosion. To the northwest these uplands merge with 

the northern highlands of northern Morazan and La Union departments, and to the southwest, with the coastal plain.

NORTHERN HIGHLANDS

The northern highlands occupy small areas between 2,000 and 6,000 

feet above sea level in the northern part of El Salvador (see pi. 3). 

They are southward extensions of the Central American Cordillera 

of southern Honduras. The land forms are in a youthful stage of 

erosion. Sharp-crested ridges with steep slopes, dissected by deep, 

narrow valleys and canyons, make up much of the topography. One 

of the most prominent ridges of the northern highlands lies east of 

the upper Rio Lempa in the northwestern part of Departamento de 

Chalatenango. Smaller highland areas occupy the northern part of 

Santa Ana, the northwestern corner of Cabanas, and the northern 

parts of San Miguel, Morazan, and La Union departments.

COASTAL PLAIN

The coastal plain of El Salvador rises inland from the shore line 

to an elevation of about 500 feet. (See pi. 3.) Near the Guatemala 

frontier the plain is about 3 miles wide and gradually merges inland 

with the western plateau. An embayment reaches inland about 12 

miles in the vicinity of Sonsonate and the Rio Grande. At La Libertad the coastal plain is only a few hundred feet wide. Westward from 

this point it widens into the lower Lempa Valley, where it reaches 

perhaps 20 miles inland. East of the Rio Lempa it narrows to a 

width of 10 to 15 miles. Southwest of Laguna del Camalotal are the

11 Op. cit., p. 73.
170 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

Colinas de Jucuaran, a dissected ridge about 18 miles long. This 

ridge rises to an elevation of about 2,500 to 3,000 feet above sea level 

and 2,000 feet above the adjacent coastal plain.

Where it merges with the plateau in the western part of the country 

and with the uplands in the east, the interior margin of the coastal 

plain is a sloping surface of erosion cut in old volcanic rocks by 

numerous parallel streams draining to the coast. Seaward this surface merges in unbroken profile with a surface of alluviation formed 

by stream deposition, with some modification by wave and current 

action.

GEOLOGY

SEQUENCE AND GENERAL FEATURES OF THE ROCKS

In El Salvador nonmarine strata of the Tertiary and Quaternary 

systems rest on igneous and sedimentary rocks of Cretaceous and 

greater age. Apparently the oldest rocks in El Salvador belong to 

the Metapan formation 12 of late Jurassic and early Cretaceous age. 

The formation includes interbedded sandstone, shale, conglomerate, 

marl, and limestone, with occasional strata of tuff and breccia. These 

rocks occur in the Metapan region of Departamento de Santa Ana 

and in the northern part of Departamento de Chalatenango. Locally 

the rocks of the Metapan formation are intruded by stocks and dikes 

of granite, granodiorite, and diorite. These intrusive rocks may be 

of late Cretaceous or possibly early Tertiary age.

The strata of the Tertiary system include extrusive basalt, andesite, 

dacite, and acidic extrusive rocks; volcanic ejectamenta that range 

from scoria to compact tuff, agglomerate, and breccia; and detrital 

sediments of alluvial and lacustrine origin. Strata of the three classes 

are interlaminated and interfingered, and they grade laterally into 

one another in a complex fashion. The rocks of the Quaternary system include basic lavas and pyroclastics erupted from central vents, 

and alluvial, lacustrine, and beach sediments deposited in larger valleys an.d basins, and along the seaward margin of the coastal plain.

SUMMARY OF THE GEOLOGIC HISTORY

According to Larde 13 and Sapper,14 and to observations of the writers, the geologic history of El Salvador appears to include the following general sequence of events:

During Jurassic and Cretaceous time marine embayments covered 

the Central American isthmus from time to time and limestone, sandstone, and shale were deposited in the submerged areas. Toward the

12 Imlay, Ralph W., Cretaceous formations of Central America and Mexico : Am. Assoc. 

Petroleum Geologists Bull., vol. 28, no. 8, pp. 1114-1116, 1944.

13 Larde, Jorge, op. cit., pp. 79-81, 1924.

14 Sapper, Karl T., op. cit., pp. 1-3, 1925.
GEOLOGY 171

end of the Cretaceous, emergence of the isthmus began, but deposition 

in the submerged areas continued until Pliocene time, when the Central 

American isthmus emerged in approximately its present form.

Volcanism began along the Pacific margin of the isthmus probably 

during the Cretaceous and continued intermittently to the present. 

The first rocks were probably extruded in fissure eruptions 15 of 

andesitic and basaltic lava with associated felsitic lavas. Later in 

Tertiary time explosive volcanic activity began, probably at closely 

spaced central vents. During this time pyroclastic materials such 

as tuff, explosion breccia, and volcanic agglomerate formed extensive 

deposits. Contemporaneously with these eruptions, erosion was active 

in the upbuilt areas, and deposition of detrital materials took place 

in the lowland valleys and basins.

According to Larde,16 Cretaceous strata and early Tertiary volcanic beds in the northern highlands of El Salvador have been deformed by folding and faulting, whereas somewhat younger strata 

in the same region have not been disturbed. This evidence would 

suggest that the structural movements probably occurred in early 

or middle Tertiary time.

The upbuilding and activity of the modern volcanoes in the central 

highlands of El Salvador probably started at the beginning of Quaternary time,17 and have continued to the present. At first great quantities of pyroclastic materials were produced by explosive eruptions, 

which later were accompanied by the extrusion of basaltic and andesitic lava.

As a consequence of the lava extrusions, drainage lines were blocked 

from time to time, and detrital sediments eroded from the neighboring highlands were deposited in the resulting ponded areas. During 

periods of quiescence at volcanic centers, streams reduced the lava 

barriers, eroded the earlier detrital and volcanic materials, and deposited alluvial sediments in low, open valleys along the coastal plain.

The general sequence, character, and water-bearing properties of 

the rock strata of El Salvador are summarized in the following table 

and are described at length on following pages:

M Sapper, Karl T., op. cit. p. 1.

16 Larde, Jorge, op,, cit., p. 33, 1924.

17 Sapper, Karl T., op. cit., p. 1.
172 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA 

Generalized stratigraphic section of the rocks of El Salvador, Central America

Geologic age

QUATERNARY

RECENT

PLEISTOCENE

Geologic unit

Beach and estuarine 

deposits.

Landslides, talus, 

and alluvial fans.

Younger alluvium.

Younger Quaternary lavas and 

pyroclastic rocks.

Older alluvium.

Older Quaternary 

lavas and pyroclastic deposits'.

Lake beds.

General character

Light-colored wind-blown sand 

in dunes along coast. Darkcolored basaltic and andesitic 

sand and gravel in beaches. 

Estuarine muck, silt, and clay 

at Bahia de Jiquilisco and 

Estero Grande de Jaltepeque.

Landslide masses in deep canyons. Talus forms aprons at 

bases of cliffs and steep slopes. 

Alluvial fans of boulder trains, 

sand and gravel deposited by 

torrential streams on steep 

slopes.

Sand, silt, and gravel derived 

from erosion of pre-existing 

rock and alluvial deposits. In 

flood plains along present 

stream channels and along 

the seaward margin of the 

coastal plain.

Basalt and andesite lavas with 

compact, scoriaceous, and 

fragmental facies. Extruded 

from adventitious vents on 

flanks of larger volcanic centers, notably San Miguel, San 

Salvador, Santa Ana, and 

Izalco volcanoes. Pyroclastic 

materials includeash, pumice, 

and cinders derived from explosive eruptions at central 

vents. Blanket the flanks of 

volcanoes of central highlands 

and neighboring areas.

Sand, gravel, and. locally, boulders. Similar to younger alluvium but is topographically 

higher. In terraces along Rfo 

Lempa and its larger tributaries.

Basalt and andesite lava flows 

with compact, scoriaceous, 

and fragmental facies erupted 

from the central and satellite 

vents of the central highlands. 

Pyroclastic materials include 

ash, breccia, pumice, and 

cinders, intercalated with 

lavas to form main mass of 

volcanoes of central highlands 

of El Salvador.

Water-laid clay, silt and sand 

derived from pyroclastic ash, 

pumice, and cinders, deposited 

in lava-dammed basin. Locally interbedded with, lava 

and subareal pyroclastic. deposits. In certain localities 

contain bones of elephants and 

other mammals.

Water-bearing characteristics

Dune sand where present in the 

zone of saturation above sea 

level yields small supplies of 

potable water to shallow dug 

wells.

Landslide and talus masses 

unimportant as water-bearing 

materials. Panglomerates 

yield considerable water when 

present in the zone of saturation, but are generally above 

the water table.

Contains considerable water at 

shallow depth in lower stream 

valleys.

These materials are commonly 

above the regional water table, 

but local perched ground-water 

bodies yield small supplies to 

shallow wells and temporary 

springs. Scoriat:eous and fragmental facies of the lavas, and 

pumiceous and cindery pyroclastic rocks are permeable and 

serve as intake areas for groundwater recharge.

Yields moderate supplies of 

water to wells where present 

in the zone 3f saturation.

Scoriaceous and fragmental facies 

of the lavas are permeable and 

supply many wells and springs 

in the republic. Pumice and 

cinder beds are ordinarily productive water-bearing horizons 

when present in the zone of 

saturation. Ash beds are ordinarily impermeable but locally 

yield small to moderate supplies of water to wells and 

springs.

Sandy and cindery beds yield 

moderate supplies of water to 

wells and springs. Clayey 

beds largely impermeable.
GEOLOGY 173

Generalized stratigraphic section of the rocks of El Salvador, Central America Con.

Geologic age

TERTIARY

CRETA- CEOUS 

(?)

JURASSIC CRETA- and

CEOUS

LATE 

TERTIARY (?)

EARLY (?) TERTIARY

«<JCQ

WEit> P^HO^,

PMtfW

t>QO

JU- UPPERRASSIC andLOWER CRETACEOUS

Geologic unit

Pyroclastic deposits 

and lavas.

Volcanic rocks and 

related sedimentary rocks.

Intrusive rocks.

Metapan formation.

General character

Pyroclastic deposits include extensive masses of andesitic 

agglomerate, breccia, and tuff 

intercalated with basalt and 

andesite lava flows. Underlie 

younger volcanic rocks and 

detrital materials of the central highland, the western 

plateau, and the coastal plain.

Weathered basaltic, andesitic, 

and felsitie lavas, with intercalated pyroclastic rocks and 

detrital sediments including 

sandstone, conglomerate diatomaceous beds, and, locally, 

carbonaceous and clay strata. 

In the northern highlands and 

eastern uplands.

Granite, granodiorite, and diorite intrusive into Metapan 

formation. In northern highlands of Santa Ana and Chalatenango departments.

Sandstone, shale, conglomerate, 

marl, and limestone with a 

few strata of tuff and breccia. 

In northern highlands of Santa 

Ana and Chalatenango departments.

Water-bearing characteristics

Fragmental and scoriaceousfacies 

of andesite and basalt lava 

yield moderate to large supplies of water to wells and 

springs where present in the 

zone of saturation. Pyroclastic 

materials ordinarily impermeable but locally yield small 

to moderate supplies of water 

to wells and springs.

These rocks generally have low 

permeability due to cementation and induration of sedimentary beds and alteration of 

volcanic materials. Fractures 

may yield small supplies to 

springs. Locally fragmental 

and scoriaceous zones in the 

lavas yield moderate to large 

supplies of good water to wells 

and springs.

These rocks are not generally 

very permeable, but fractures 

and weathered zones may yield 

small supplies to wells and 

springs.

These rocks are not generally 

very permeable but may yield 

small supplies to wells and 

springs from fractures or solution passages.

PHYSICAL CHARACTER AND WATER-BEARING PROPERTIES OF

THE STRATA

QUATERNARY SYSTEM

RECENT SERIES 

BEACH AlTO ESTUABINE DEPOSITS

Along the coast of El Salvador are extensive beaches with local dune 

ridges, bars, and estuaries. The beaches are commonly composed of 

dark-colored sands and gravels of andesitic and basaltic composition. 

They are best developed where the coastal plain is relatively narrow 

and competent. streams carry large amounts of coarse material to 

the shore line. The dune ridges occur in favorable localities along 

beaches with prevailing onshore winds and with abundant sand. The 

dune sands are generally made up of the lighter particles of the sands 

composing the beaches.

The beach deposits, sand bars, and dune ridges are permeable to 

water. Where these materials are saturated with fresh water to a 

height of a few feet or more above sea level, they furnish small domestic supplies to shallow dug wells. Such water supplies are used by 

fishing villages near Bahia de Jiquilisco Bay, Estero Grande de 

Jaltepeque, and other scattered localities along the coast. -.

930754 51 4
174 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

The estuarine deposits are made up of organic muck, silt, and clay 

laid down in tidal flats and anastomosing channels on low, swampy 

shore lines. They are best developed where the coastal plain is wide 

and the streams entering the sea are sluggish. The chief present sites 

of estuarine deposition are Bahia de Jiquilisco, between the outlets of 

the Rio Lempa and Rio San Miguel, and Estero Grande de Jaltepeque 

between the outlets of the Rio Jiboa and Rio Lempa. Each of these 

bays is protected by a sand bar that parallels the coast and rises 

a few feet above sea level. These bars apparently have been formed 

by the action of longshore currents and by wave action during storms. 

The estuarine deposits have very low permeability, and, moreover, 

they lie within the range of tidal fluctuations. Hence they yield no 

potable water to shallow wells.

LANDSLIDES, TALTJS, AND ALLUVIAL FANS

Throughout El Salvador, landslides, talus aprons., and alluvial fans 

occur in favorable situations. Notable landslides are associated with 

Pleistocene and Recent volcanic materials along the scarps surrounding Laguna de Ilopango, in the adjacent canyon of the Rio Jiboa, 

and in stream canyons draining north to the Rio Lempa from the 

San Salvador highland. Conditions favorable to the development 

of landslides appear to include the following principal factors: An 

unstable slope, perhaps oversteepened by stream erosion at its base; 

a gliding plane such as a saturated clay stratum; and a heavy competent bed overlying a relatively weak or unconsolidated bed. These conditions are often attained along streams that have cut deep canyons 

into heavy lava flows or masses of volcanic agglomerate overlying 

soft layers of tuff, pumice, and cinders. Sliding take's place when 

intercalated layers of clay or old soil zones become saturated. Most 

of the present landsliding occurs in the wet season after torrential 

downpours of several days' duration.

Talus aprons or slopes are developed in the summit areas of the 

active volcanic peaks where the vegetative cover is poor or lacking. 

Rock streams several hundred feet long, composed of loose lava blocks, 

clinkers, and cinders, are common on the upper, outer slopes of San 

Miguel, Usulatan, Boqueron, Izalco, and Santa Ana volcanoes. Talus 

aprons skirt the infacing walls of the summit craters of all these 

peaks.

Alluvial fans of small extent occur around the bases of the principal 

volcanoes at the lines of convergence of the steep upper .slopes and 

the gently inclined lower slopes. They are formed by deposition 

from ephemeral streams which drop their loads of detritus in their 

lower courses where the gradient becomes less steep. These streams 

flow only after heavy rainstorms on the upper slopes of the volcanoes.
GEOLOGY 175

The fan material is" usually coarse but poorly sorted. Most of the 

material is composed of coarse sand with cobbles and pebbles, but 

boulders several feet in diameter are not uncommon. Small alluvial fans have also been observed in localities where torrential 

streams with steep gradients debouch from narrow canyons on to flood 

plains with low gradients. A typical example is the fan formed by 

the Quebrada Seca, which enters the Lempa flood plain from the west 

just above the mouth of the Rio Acahuapa.

The landslide masses are too small and restricted to be of importance 

as water-bearing formations in El Salvador. The talus aprons and 

slopes are generally above the regional water table and are probably 

rather thoroughly drained. However, because of their permeability 

they are locally important as catchment areas for the precipitation 

that falls on the upper slopes of the volcanoes. They tend to divert 

water underground rather than to allow it to run off. on the surface. 

The alluvial fans are generally above the water table, but locally their 

basal parts are saturated and water overflows in small perennial 

springs. The headwater tributaries of the Rio Jiboa and Rio 

Acahuapa that drain off the slopes of Volcan Chichontepec are fed in 

part by springs of this type.

YOUNGER ALLUVIUM

The younger alluvium forms the bars and banks, and floors the 

channels of the Rio Lempa, Rio Jiboa, Rio San Miguel, and their larger 

tributaries. In places it underlies the seaward margin of the coastal 

plain and veneers pediment surfaces of the interior margin. It usually 

comprises sand, silt, and water-worn gravel. Along the Rio Lempa it 

generally is reworked older alluvium mixed with basaltic and andesitic 

pebbles and cobbles of local origin. According to Larde 1S it contains 

pebbles of limestone, granite, diorite, basalt, and andesite along the 

southern margin of Departamento de Chalatenango. Downstream 

the percentage of locally derived material increases. The younger 

alluvium along the Rio San Miguel consists of materials derived 

principally from basic and silicic lavas and pyroclastics of probable 

Tertiary age. The seaward margin of the coastal plain is underlain 

by sand, gravel, and silt deposits of similar origin from the mouth 

of the Rio San Miguel to the mouth of the Rio Lempa. Along the 

Rio Jiboa the younger alluvium includes materials from basic lavas 

and pyroclastics of Recent and Pleistocene age. Similar materials 

underlie the coastal plain from the mouth of the Rio Jiboa to the 

mouth of the Rio Lempa and veneer the pediment surface of the 

inland margin of this plain. From Sonsonate south to the shore line

18 Larde, Jorge, Geologla general de Centre-America y especial de El Salvador: Imprenta 

Nacional, San Salvador, p. 34, 1924.
176 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

is a wide embayment of the coastal plain which-is veneered in part 

by stream deposits of the Rio Grande and neighboring streams.

The younger alluvium along most of the stream valleys is quite 

permeable. Where it is saturated in its lower part, it yields moderate 

to large supplies of water to wells of shallow depth. Domestic wells 

develop water from this source along the Rio Lempa, especially below 

the mouth of the Rio Acahuapa and along the lower courses of the 

Rio Jiboa and Rio San Miguel.

YOUNGER QUATERNARY LAVAS AND PYROCLASTIC DEPOSITS

A large part of the central highlands and adjoining areas of El 

Salvador is covered by soft to semiconsolidated pyroclastic materials 

interbedded with lava flows of probable Recent age. These materials 

make up the minor lava domes and cinder cones around the bases 

and on the flanks of the major volcanic peaks. They also compose 

much of the material in the summit areas of the volcanic peaks, 

including vent and explosion breccias in the summit craters. The 

pyroclastic materials include principally beds of ash and pumice, 

interbedded with lesser amounts of cinders and explosion breccia. The 

pyroclastic fragments are commonly less than a foot in diameter. 

The lava flows include chiefly andesite and basalt. The upper and 

basal parts of the flows are ordinarily vesicular, but the interior parts 

are compact. The tops of some of the flows are blocky and fragmental, whereas others are relatively smooth and ropy.

Most of the lava flows were extruded from adventitious vents on 

the flanks of the major volcanoes and for this reason are more localized than contemporary pyroclastic deposits, which are distributed 

by air currents. Conspicuous lava flows around the bases of San 

Miguel, San Salvador, and Santa Ana volcanoes are of such recent 

date that original volcanic surfaces have not been scarred by erosion 

and a soil cover has not been developed by weathering, even under 

the extreme tropical conditions.

Most of the pyroclastic material that blankets the central highlands 

originated in explosive eruptions at the main vents of the principal 

volcanoes of the central highlands. The coarser materials, including 

breccias, agglomerates, and cinders, were deposited on the flanks and 

in the vicinity of the volcanoes. The finer ash and pumice were 

carried farther by air currents and deposited over wider areas. The 

younger Quaternary pyroclastic materials and lavas merge downward 

imperceptibly with similar rocks of Pleistocene age and can be distinguished from them only by the absence of weathering and the degree 

of freshness of original constructional surfaces.

The finer-grained pyroclastic materials, equivalent in grain size 

to silt and clay, are essentially impermeable. The coarser materials, 

including pumice and cinders, are moderately to highly permeable.
GEOLOGY 177

Volcanic breccias and agglomerates, because fine material fills the 

interstices between large fragments, have a low but appreciable 

permeability.

The massive fades of the lava flows are essentially impermeable. 

On the other hand, there is considerable permeability in the blocky and 

fragmental zones that constitute the upper and lower parts of some 

layers, in the interspersed sheets and tongues oj: scoria, and in fractured zones. Altogether these permeable facies have considerable 

aggregate capacity to transmit water.

The younger Quaternary pyroclastic deposits and lavas lie above 

the regional water table over much of the area in which they occur 

and hence are generally rather thoroughly drained. However, tha 

permeable facies of these rocks are important as ground-water catchment areas, for they tend to divert rainwater underground rather 

than to allow it to run off over the surface.

The permeable facies of the lava flows, cinder, and pumice beds 

supply small temporary springs which are fed by local bodies of ' 

perched ground water. Such springs usually fail, a few weeks after 

the dry season begins, and they do not flow again until the first heavy 

rains of the wet season have renewed the depleted ground-water storage. Along the Pan American Highway between San Salvador and 

Cojutepeque, and in many other sections of the country, springs of 

this type are used as temporary sources of water by rural inhabitants 

and travelers. Many of these springs rise from thin beds of pumice 

that overlie impermeable ash beds. Others rise from fissures, crevices, 

or other pervious zones in aiidesite or basalt flows above compact 

lava. Most of these springs flow in direct response to heavy rainstorms, and the dry-weather flow is markedly lower. Few of the 

springs from the younger pyroclastics and lavas that were observed 

yield more than a few gallons a minute on the average.

PLEISTOCENE SERIES 

OLDER ALLUVIUM

The older alluvium forms terraces 25 to 50 feet above the present 

stream beds. It occurs as scattered remnants in protected places along 

the Eio Lempa and its larger tributaries. With the exception of these 

remnants the terraces have been largely destroyed in the present cycle 

of stream erosion.

The older alluvium consists chiefly of gravel, sand, and silt. Along 

the Eio Lempa the finer material is more abundant below the mouth

of the Eio Acahuapa, anc 

In some places the older 

stream bed, but in other

coarser materials more abundant upstream, 

alluvium appears to pass under the present 

places it is only a thin veneer on rock-cut

surfaces. The older alluvium includes fragments that are chiefly of
178 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

the resistant rock types that crop out in the headwaters of the Bio 

Lempa, which rises in the highlands of the Central American isthmus. 

The rock types include silicic and basic lavas, crystalline and metamorphic rocks, and limestone. Local rock types are not as commonly 

present as they are in the younger alluvium.

The sand and gravel facies of the older alluvium are quite permeable, and may yield moderate supplies of water to wells where 

present in the zone of saturation. However, because of their limited 

areal extent, and elevation above present stream levels, these deposits 

are not important as water-bearing materials in El Salvador.

OU>EB QUATERNARY LAVAS AND PYROCLASTIC DEPOSITS

The main masses of the large volcanoes comprising the central 

highlands of El Salvador are made up of lava and pyroclastic materials of probable Pleistocene age. These materials underlie and grade 

upward into Kecent lavas and pyroclastic deposits, from which they 

differ principally in degree of weathering and consolidation. They 

include basalt and andesite lava flows and pyroclastic rocks that are 

chiefly ash and pumice with lesser amounts of volcanic breccias, agglomerates, and cinders. The lava flows occur in compact, scoriaceous, 

and f ragmental f acies, and are intercalated with the pyroclastic rocks. 

Most of these materials apparently originated in eruptions at the 

principal vents of the central highlands.

The basin of Lago de Giiija on the Guatemala frontier was probably 

formed during the Pleistocene by lava flows from neighboring volcanoes that blocked the local drainage. Larde 19 believes this lake is 

now considerably smaller than formerly, owing to the recent filling 

of the basin by sediments and the lowering of the outlet by stream 

down cutting.

In the Apaneca-Santa Ana highland large masses of basalt and 

andesite lava of probable Pleistocene age are present on the north 

flank but are not found to the south. In pyroclastic deposits erupted 

from volcanoes composing this highland abundant remains of mastodons of Pleistocene age have been found at a place called Huesera 

in the canton of Guineo, a few miles north of Laguna de Coatepeque.

According to Larde 20 the Sonsonate area is also underlain by lava, 

ash, and cinders formed by Pleistocene eruptions of neighboring 

volcanoes.

The masses of San Salvador and Boqueron volcanoes are composed 

chiefly of basaltic and andesitic lava flows interbedded with breccias, 

ash, pumice, and cinders. Plant fossils and elephant remains have 

been found in pyroclastic materials erupted from these volcanoes near

19 Larde, Jorge, op. cit., p. 24, 1924.

20 Op. cit., p. 32.
GEOLOGY 179

Colon, near Jayque, and near the city of San Salvador. According 

to Larde these fossils resemble present forms and suggest the Pleistocene age of the main mass of these two volcanoes.

The main mass of the San Vicente highland and of the Tecapa-San 

Miguel highland also appear to be made up chiefly of Pleistocene 

lavas and pyroclastic rocks. Fossil insects and elephant remains reported to occur in the tuffs at Sisimico, near San Vicente, suggest that 

the last eruptions from volcanoes in this vicinity took place in Pleistocene time.21

The scoriaceous and fragmental facies of the lava flows are highly 

permeable to water and supply many wells and springs in the republic. 

Pumice and cinder beds ordinarily are productive water-bearing horizons when present in the zone of saturation. The ash beds have low 

permeability and yield only meager supplies of water to wells.

In the city of San Salvador some 20 wells obtain their supplies from 

the scoriaceous and fragmental zones of a basaltic lava bed of probable Pleistocene age. Wells ending in this stratum at depths ranging 

from 100 to 325 feet are reported to yield 500 to TOO gallons a minute 

with little drawdown. The springs of La Chacra and El Coro at the 

eastern outskirts of San Salvador flow from the same stratum. Each 

of these! springs discharges several hundred gallons a minute with 

little variation in flow during the year.

About 3 miles west of Nueva San Salvador on the Pan American 

Highway are the springs of Los Chorros, which issue from a bed of 

permeable cinders overlying an impermeable stratum of volcanic tuff. 

The discharge of these springs, estimated at 1,200 gallons a minute, is 

reported to be relatively constant throughout the year. Near Quezaltepeque, Antiguo Cuscatlan, and San Martin are springs rising 

from similar materials. The discharges of these springs range from 

10 to 1,500 gallons per minute.

LAKE BEDS

Water-laid deposits of clays, silts, and sands of volcanic origin 

underlie considerable portions of the plains, basins, and valleys of the 

western plateau of El Salvador. Most of these materials were probably deposited in shallow lakes or swamps, but near the highland 

margins are occasional interbedded stream deposits, lava flows, and 

subareally deposited pyroclastic materials.

The extensive plain of Candelaria, lying between Ilio.de Paz, Volcan 

Chingo, and the northern foothills of the Apaneca-Santa Ana highland, appears to be underlain in large part by lake or swamp deposits. 

Larde 22 has suggested that the basin in which these deposits were laid 

down was formed as a result of the upbuilding of the surrounding

21 Larde, Jorge, op. cit., p. 45.

22 Op. cit., p. 27.
180 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

volcanic masses. The basin was then filled with materials eroded from 

the neighboring highlands. Subsequently the Rio de Paz cut headward through the highland barrier and drained the basin. This stream 

is now entrenched, and its tributaries have deeply dissected the basin 

deposits.

Near San Lorenzo, Departameiito de Ahuachapan, elephant remains 

of probable Pleistocene age are reported to have been found in waterlaid, cream-colored pumiceous clays. In the vicinity of El Ref ugio in 

the same department, tuffaceous silt, clay, and sand underlie the surface to depths of 100 to 150 feet. Similar materials underlie the plain 

of Candelaria from the city of Santa Ana west and northwest to the 

Guatemala frontier.

Lacustrine and swamp deposits of probable Pleistocene age underlie a large part of the lowland plains and valleys between the San 

Salvador highland to the south, the Apaneca-Santa Ana highland 

to the west, the northern highlands of the Departamento de Chalatenaiigo to the north, and the Cojutepeque highland to the east. This 

lowland includes three contiguous subareas. They are the Zapotitan 

basin between the Apaneca-Santa Ana highland and the San Salvador 

highland, the plain of Aguilares lying north of the San Salvador 

highland and south of the Rio Lempa, and the plains of Chalatenango 

lying south of the city of Chalatenango and north of the Rio Lempa.

Larde 23 has suggested that a lake of considerable size may have 

existed in this lowland area during the late Pliocene or early Pleistocene. The development of such a lake is attributed to the blocking 

of the Lempa drainage by volcanic accumulation in. the area near 

the present mouth of the Rio Sumpul. Sediments carried by streams 

draining from the neighboring highlands were deposited in the basin 

area. At some later time the Rio Lempa lowered its outlet from the 

lake and- its tributary streams, adjusting to the lowered base level, 

entrenched themselves in the basin deposits.

Much of the Zapotitan basin is underlain by water-laid deposits 

of silt, clay, "and occasional beds of sand of volcanic origin. Near the 

junction of the Rio Sucio with the Rio Lempa, laminated micaceous 

clays are reported to occur. Similarly, the plains of Aguilares and 

Chalatenango appear to be underlain principally by massive tuffaceous silt and clay with occasional beds of sand.

South of San Francisco, in the eastern uplands of El Salvador, is 

a lowland area almost completely surrounded by hills and ridges. 

Larde 24 reports that earthy deposits underlying parts of the lowland 

contain remains of Pleistocene mastodons in vertical position. He 

suggests that the animals were trapped in swamps in which the sediments were deposited.

» Op. cit., p. 36. 

24 Op. cit, p. 43.
GEOLOGY 181

The silt and clay beds of the lake deposits are essentially impermeable and yield little or no water to wells. The sandy beds have 

moderate permeability and yield small supplies to wells. Locally, 

interbedded strata of cinders or pumice occur in the deposits. Where 

these strata are present in the zone of saturation, they yield moderate 

to large supplies of water to wells.

In Departamento de San Salvador, from Guazapa along the San 

Salvador-Tejutla road to the Eao Lempa, dug wells obtain small 

domestic supplies from pervious alluvial or lacustrine deposits at 

depths of less than 100 feet. Near Atiquizaya, in Departamento de 

Ahuachapan, are numerous swampy areas fed by springs issuing from 

a bed of sand and cinders. Many of the individual springs flow from 

10 to 50 gallons a minute, and aggregate discharges from the swamp 

are'as range from 500 to 2,000 gallons a minute. Dug'wells from 25 

to 35 feet deep in the town of Atiquizaya obtain domestic supplies 

from the same stratum. The lake-bed deposits also supply springs 

and wells to the northwest of Santa Ana, in the Zapotitan basin, and 

in the southern part of the Departamento de Chalatenango near the 

Rio Lempa.

TERTIARY SYSTEM

LATE TERTIARY (?) PYROCLASTIC DEPOSITS AND LAVAS

The greater part of the central highlands, the western plateau, the 

coastal plain, and the eastern uplands are underlain by volcanic rocks 

of probable late Tertiary age. These rocks do not crop out extensively 

at the surface except in the eastern uplands. They are made up in 

large part of pyroclastic materials, including extensive masses of 

volcanic agglomerate, breccia, and tuff that locally are interbedded 

with lava flows. The widespread distribution of the pyroclastic materials seems to indicate the predominance of explosive volcanic activity over liquid eruptions during the late Tertiary, for flow rocks 

are relatively restricted in their occurrence. Andesitic and basaltic 

materials are the most common flow-rock types, dacite rocks crop out 

in many places in the eastern uplands, and rhyolites occur locally.

According to Larde and the observations of the writers, andesitic 

agglomerate crops out from beneath younger rocks in many places 

in the Apaneca-Santa Ana highland, in the Sonsonate and Ahuachapan areas, and on the edges of the Zapotitan basin. North and northeast of the Zapotitan basin it crops out occasionally from beneath 

younger rocks as far as the valley of the Bio Lempa. The agglomerate strata over most of this area consist chiefly of heterogeneous, 

unsorted masses of andesite lava fragments enclosed in tufiaceous or 

clayey matrix. The rock fragments range from the size of pebblesto boulders several feet in diameter.

930754 51 5
182 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

The coast range, Cadena Costera, which lies to the south of Laguna 

de Ilopango and the city of San Salvador, is made up of volcanic 

rocks which in large part are inferred to be of late Tertiary age. These 

rocks include tuffaceous clays and compact andesitic agglomerates with 

occasional intercalated basalt and andesite lava flows.

North of Laguna de Ilopango andesitic agglomerate crops out occasionally from beneath a cover of Recent and Pleistocene pyroclastic 

deposits of Volcan de San Salvador and Volcan Guazapa.

The Cojutepeque volcanic highland is also built up on a platform 

of compact andesitic agglomerate and tuff. This relation would suggest a Pleistocene age for at least Volcan Cojutepeque and its surrounding field of soft or semiconsolidated ash and pumice deposits.

The late Tertiary (?) rocks are exposed almost continuously in the 

southward-facing escarpment overlooking the valley of the Rio 

Acahuapa. Road cuts along the Pan-American Highway, which follows this escarpment, between kilometers 50 and 55 east show a heterogeneous assortment of volcanic breccia, agglomerate, and tuff with 

occasional interbedded lava flows.

The Tecapa-San Miguel highland apparently is also built up on a 

base of late Tertiary (?) rocks, but these are almost completely covered by younger rocks erupted from the volcanoes of the highland. 

South of the valley of the Rio Sesori, clayey andesitic agglomerates 

with occasional basalt intrusions are reported to occur.23 These rocks 

are probably of late Tertiary age.

The coastal plain south of the Tecapa-San Miguel highland, between 

the Rio Lempa and Rio San Miguel, is underlain by beds of clayey 

andesitic or basaltic agglomerate. Over most of the area these beds 

are covered by younger detrital and volcanic materials. The contiguous plain to the southeast of San Miguel is underlain by similar rocks.

Larde 26 reports that clayey agglomerates intercalated with basalt 

and andesite lava flows make up most of the Colinas de Jucuaran, 

which lie near the coast southwest of Laguna del Camalotal.

The capacity of the late Tertiary (?) rocks to transmit water varies 

widely. The volcanic agglomerates, breccias, and tuffs which compose 

the pyroclastic facies of the rocks generally have low permeability. 

The low permeability of the agglomerates is due to the tight, finegrained tuffaceous material that fills the voids between rock fragments. Locally the breccias are highly permeable owing to the absence 

of fine material between angular rock fragments. Except for secondary tabular partings, the tuff beds are essentially impermeable. When 

these partings are present, the tuff beds have the capacity to transmit 

water slowly.

25 Larde, Jorge, op. cit., p. 47. 

28 Op. cit., p. 51.
GEOLOGY 183

In spite of their low permeability the late Tertiary (?) pyroclastic 

rocks yield small supplies of water to shallow dug wells and sustain 

small perennial springs in many parts of the country. For example, 

at Tejutepeque in the Departamento de Cabanas dug domestic wells 

obtain small water supplies from pumice lenses and tabular partings 

in volcanic tuff and agglomerate at depths of 20 to 30 feet. Water 

supplies from similar rocks and at comparable depths are obtained 

by domestic dug wells at Chapeltique and Chirilagua in Departamento 

de San Miguel and at San Carlos and Jocoro in Departamento de 

Morazan. At the village of El Carmen near Cojutepeque a spring 

issuing from sand streaks and partings in aiidesitic agglomerate has 

been developed for the public supply. In this same region are several 

other small springs that rise from volcanic tuff and agglomerate.

Intercalated with the pyroclastic rocks are basalt and andesite lava 

flows. The massive facies of the interior parts of the lava flows 

are essentially impermeable, but the blocky and fragmental zones that 

form the upper and lower parts of some layers may be quite permeable. These zones, together with interspersed sheets and tongues of 

scoria and fracture zones, have considerable aggregate capacity to 

transmit water. For example, near Panchimalco the springs of La 

Catarata issue from joints and fissures in a tongue of aiidesitic lava 

above an impermeable bed of tuff and breccia. The flow of these 

springs, estimated at 1,200 gallons a minute, is relatively constant 

throughout the year.

At Usulatan are the springs of Molinos, which are among the 

largest in El Salvador. The combined discharge of the three principal spring heads is estimated at 50 cubic feet per second or approximately 22,500 gallons a minute. The springs issue from a tongue 

of late Tertiary (?) andesitic lava in the scoriaceous and fractured 

zone above the contact with an underlying stratum of tuff.

The large springs of Inchanmichen and Santa Irene near 

Zacatecoluca and the springs of Las Daiitas which supply the city of 

San Salvador also issue from late Tertiary (?) flow rocks or 

open-textured volcanic breccias.

EARLY TERTIARY VOLCANIC ROCKS AND RELATED SEDIMENTARY ROCKS

A diverse group of volcanic and sedimentary rocks underlies large 

parts of the northern highlands, the eastern uplands, and adjacent 

areas bordering on the Honduras frontier. These rocks underlie late 

Tertiary (?) rocks and rest on rocks of probable Cretaceous age. 

For this reason they are considered to be of probable early Tertiary 

age. The writers have not critically examined these rocks, and hence 

the following discussion is based principally on observations by Larde 

and Sapper.

The early (?) Tertiary rocks include weathered extrusive lavas of
184 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

andesite and basalt with associated phonolite, trachyte, dacite, and 

rhyolite. These rocks are interbedded and intercalated with pyroclastic volcanic rocks and detrital sediments that include sandstones, 

conglomerates, and, locally, beds of diatomaceous materials and carbonaceous clays.

Sapper ""' suggests that the lavas were extruded principally in fissure eruptions during the upbuilding of the Central American 

Cordillera, but the widespread occurrence of interbedded pyroclastic 

materials would seem to indicate that explosive eruptions from central 

vents were common during the deposition of these materials.

During the accumulation of the lavas, streams apparently were 

actively eroding adjacent upland areas and depositing detrital materials in low areas. These materials were incorporated with the 

lava flows and pyroclastic rocks as sandstone and conglomerate. The 

diatomaceous beds and carbonaceous clays possibly were laid down in 

shallow lake basins formed by the damming action of the lava flows.

In the Sierra de Alotepe of the Metapan area, in northern Santa 

Ana, gray and green porphyries, andesites, and phonolites are reported to occur.28 Similar rocks with conglomerate, sandstone, and 

diatomaceous sediments make up much of the mass of the Sierra de 

Chalatenango in the northern part of Departamento de Chalatenango. 

Near the city of Chalatenango beds of lignite and carbonaceous clay 

are reported to be associated with the extrusive rocks.

According to Larde 29 the dissected plateau between the Rio Torola 

and Rio Sesori and to the east of the Rio Lempa is underlain by hard 

shales, conglomerates, laminated clays, carbonaceous sediments, 

porphyries, and ancient volcanic rocks. These rocks he considers to 

be equivalent to similar rocks in the northern part of Departamento 

de Cabanas near Jutiapa and Ilobasco. The hills of San Francisco 

and Sociedad in the central part of Morazan are also made up of volcanic rocks of probable early Tertiary age.

Larde 30 reports the occurrence of hard shale, conglomerates, pyroclastics, and siliceous lavas in the central and northern parts of Departamento de La Union. Near Santa Rosa, carbonaceous beds similar 

to those near Ilobasco and Jutiapa are reported.

Petrographic examinations have been made by Hague and Iddings31 

of several types of the early (?) Tertiary rocks in various parts of the 

Republic. Pyroxene andesites and hornblende-pyroxene andesites 

occur in several localities near the Rio Sumpul for a distance of 15

27 Sapper, Karl T., Los volcanes de la America Central; Studien iiber Amerika untl 

Spanien,, no. 1, p. 38, Halle (Saale), Max Niemeyer, 1925.

28 Larde. Jorgp, op. cit.. p. 22.

29 Op. cit., p. 41, 4.

30 Op. cit., p. 49.

31 Haa;ue. A., and Iddinps, .T. P.. Notes on the volcanic rocks of the Republic of El Salvador, 

Central America : Am. Jour. Sci., vol. 32, 3d ser.. pp. 26-31, 1886.
GEOLOGY 185

miles above its mouth. Da cite occurs along the highway 3 to 4 miles 

northeast of Jocoro, near Santa Rosa, about 9 miles east of Chalatenango, and in many other localities where the early (?) Tertiary rocks 

are exposed.

The tuffs and tuffaceous agglomerates that make up the pyroclastic 

facies of the rocks are usually composed of dense and impermeable 

materials. In many localities, however, small secondary joint planes 

and partings are well developed. These openings give the rock considerable permeability and capacity to transmit water.

The detrital sandstones and conglomerates interbedded with the 

lava flows and'pyroclastic materials generally have low permeability 

because their initial pore spaces have been largely destroyed by induration and cementation. Secondary openings generally are not 

well developed.

The capacity of the early (?) Tertiary rocks to transmit water varies 

widely, owing to the heterogeneity of the rock types. The lavas generally have lower permeability than similar rocks of younger age. In 

many areas they have been considerably altered by weathering or 

hydrothermal action, and as a result "their initial permeability has 

been reduced. Locally the scoriaceous and fragmental facies of the 

lava flows are sufficiently permeable to sustain small springs and yield 

small to moderate water supplies to wells.

Typical examples of the occurrence of water in the early (?) Tertiary rocks are found at Sensuntepeque, San Francisco, and Santa 

Rosa. At Sensuntepeque in Cabanas the three principal springs used 

by the townspeople for water supply rise from rocks of probable early 

Tertiary age. Each of these springs rises from tabular openings in 

dense, indurated volcanic tuff which forms the hill on which the town 

is situated. The average discharge of each spring is about 50 gallons 

a minute, and the flows are relatively constant throughout the year. 

At San Francisco and Santa Rosa dug wells 25 to 50 feet deep obtain 

small domestic supplies from tabular openings in dense tuffs and 

tuffaceous agglomerates. The springs of Las Anonas and Chorreras, 

which supply the town of Santa Rosa, issue from joint planes and 

fractures in andesitic lava flows. The combined discharge of these 

springs is about 25 gallons a minute.

CRETACEOUS AND JURASSIC SYSTEMS 

LOWER CRETACEOUS AND UPPER JURASSIC SERIES

Metapdn formation. Underlying the early Tertiary volcanic rocks 

and cropping out in several areas along the northern frontier of El 

Salvador are interbedded sandstone, shale, conglomerate, marl, and 

limestone with occasional strata of tuff and breccia. These rocks, the 

Metapan formation, are of Lower Cretaceous and Upper Jurassic age.
186 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

They are especially well developed in the Metapan region in the northern part of the Departamento de Santa Ana. Solution cavities in 

limestone beds are common, and caves with secondary stalactite and 

stalagmite deposits are reported in a few localities. ' Dolomitic limestones occur in the mountains east of the Rio Lempa on the Honduras 

frontier, and crystalline limestones are found along the headwater 

tributaries of the Rio Sumpul.

The water-bearing properties of the sedimentary rocks have not 

been examined by the writers. It is probable that they generally 

have low permeability, although locally, where solution openings are 

present, the limestone strata may supply large springs.

Locally the rocks of the Metapan formation are intruded by dikes 

and stocks of granite, granodiorite, and diorite. These rocks are 

thought to be of late Cretaceous age but possibly are early Tertiary. 

They occur extensively in the Metapan area of Departamento de Santa 

Ana. According to Larde 32 they also appear near Tejutla, Dulce 

Nombre de Maria, and San Francisco Morazan in Chalatenango. 

These rocks are of only local occurrence and are not important as 

sources of ground-water supply. Probably they are not generally 

very permeable, but fractures in them may supply small amounts of 

water to springs.

GROUND WATER

INTRODUCTION

Essentially all the water that occurs in the rocks of El Salvador 

originates as rain. Except in areas of active volcanism little of the 

water in El Salvador is so warm or contains so much dissolved matter 

that it can be considered connate or juvenile. A part of the rainfall 

returns £o the atmosphere by direct evaporation from the land surface, 

a part flows directly to the streams and is carried away, and another 

part seeps into the soil and rocks. Of this last part some is also returned to the atmosphere by evaporation from the soil and by transpiration of plants. The rest percolates downward through cracks, 

crevices, and interstices of the rocks until it reaches the water table 

the upper surface of the zone of saturation below which all openings are saturated with water. The water in the saturated zone below 

the water table is known as ground water. The water moves slowly 

under the influence of gravity toward areas of lower elevation, where 

it flows into bodies of surface water or is discharged by evaporation 

and transpiration.

Where permeable rocks are present in the space between the land 

surface and the water table, the ground-water body exists as if impounded in a reservoir and its upper surface, the water table, is free

82 Op. cit, p. 33.
DEPARTAMENTO DE AHUACHAPAN 187

to rise or fall as water is added to or discharged from the rocks. The 

water table may rise during or after protracted heavy rainfall as more 

of the rock is saturated and may fall during dry periods as part of 

the.rock is unwatered by evaporation, by transpiration, and by discharge through seeps and springs.

In El Salvador the fluctuations of the water table reflect the seasonal distribution of the rainfall. The water table reaches its highest stages in October or November at the end of the rainy season. The 

lowest stages usually occur at the end of the dry season in April or 

May.

The rise of the water table during the rainy season is a measure of 

the accumulation of water in underground storage. It indicates the 

excess of replenishment over loss by natural discharge in spring flow, 

in evaporation, and in transpiration of plants.

The water accumulated underground in the rainy season is dissipated by the flow of springs and other discharge during the dry season. The loss in storage during this season is indicated by the decline 

of the water table in wells and the gradual diminution of spring flow. 

In El Salvador the dry-season flow of streams is sustained almost 

entirely by spring discharge, as very little rainfall occurs during this 

period.

GROUND-WATER RESOURCES BY DEPARTMENTS 

DEPARTAMENTO DE AHUACHAPAN

GENERAL FEATURES

The Departamento de Ahuachapan is in the extreme western part 

of El Salvador. (See pi. 3.) It has an area of about 830 square miles 

and a population of about 91,000. The department includes the western part of the Apaneca-Santa Ana highland of the central highlands 

district, parts of the western plateau district including the southern 

extension of the plain of Candelaria, and the extreme western part of 

the coastal^plain district (pi. 3).

Within the department the Apaneca-Santa Ana highland is underlain by Recent, Pleistocene, and late Tertiary (?) pyroclastics and 

lavas. The plains of Candelaria are underlain by Pleistocene lacustrine deposits and pyroclastics. The seaward margin of the coastal 

plain is formed of beach, bar, and dune deposits. Young alluvial deposits of silt, sand, and gravel mantle the surface of the coastal plain, 

a seaward-sloping surface cut on pyroclastic and flow rocks of late 

Tertiary (?) and Pleistocene age. Similar rocks underlie the section 

of the western plateau between the Apaneca-Santa Ana highland and 

the coastal plain.
188 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA 

GROUND-WATER CONDITIONS

The lacustrine deposits that underlie the plain of Candelaria include 

water-laid tuffaceous silts with interbedded strata of pumiceous and 

cindery sand and gravel. Pyroclastic deposits of similar physical 

character are interbedded with the lacustrine deposits along the margins of the plain. The silts, clays, and fine sands that compose most 

of the lacustrine deposits are largely impermeable, but interbedded 

strata of sand and gravel yield small to moderate supplies of water 

to dug wells and springs. The position of the regional water table 

beneath the plain is controlled largely by the drainage level of the 

larger stream valleys and canyons that are tributary to the Rio de Paz. 

These streams rise on the northern slopes of the Apaneca-Santa 

Ana highland and drain north and northwest across the plain of 

Candelaria.

The lower parts of these streams are perennial, being fed in the dry 

season by springs that rise along the stream channels. Commonly the 

springs issue along seepage lines from beds of pumiceous or cindery 

sand and gravel overlying impervious strata of tuffaceous silt or clay. 

The yield of individual springs is small, but the aggregate discharge 

of the springs along a line of seepage may amount to as much as 50 

to 100 gallons a minute.

These spring lines represent outcrops of the regional water table. 

Generally wells for domestic and stock supplies in the plain of Candelaria must be dug approximately to the level of the spring lines to 

obtain adequate water supplies. In the vicinity of Atiquizaya the 

depth to water ranges from about 25 to 35 feet. At El Eefugio a 

perched water table occurs about 200 feet below the land surface, 

but 21^ miles east of town the regional water table at one well is 

reported to be more than 350 feet below the surface. About iy2 miles 

southeast of El Eefugio dug wells on the Mendoza and Salazar coffee 

plantations obtain small domestic supplies at depths of 160 to 180 feet. 

These wells end in water-bearing beds of cindery sand interbedded 

with tuffaceous silt.

In the Apaneca-Santa Ana highland of Ahuachapan department 

there are few wells, but numerous springs of small to moderate flow 

emerge in the canyons draining to the north and to the south of the 

highland ridge. Springs are the principal source of water supply in 

this region, and many have been developed for municipal and domestic 

use and for the washing of coffee at coffee plantations.

The permanence of a spring in this region depends principally on 

the size and extent of the ground-water intake area contributory to 

it. The high-level springs on the upper slopes of the volcanoes generally fail in the dry season, but springs in the deeper canyons are 

perennial. Most of the perennial springs in the Apaneca-Santa Ana
DEPARTAMENTO DE AHUACHAPAN , 189

highland issue from Pleistocene and late Tertiary (?) rocks. , The 

springs issuing from Recent rocks are generally temporary. Many of 

the larger springs in the highland issue from tongues of jointed and 

fractured Pleistocene andesitic lava interbedded with impermeable 

volcanic tuff and agglomerate. Many springs are found in the deeper 

canyons and issue from lava above the contact with underlying impermeable pyroclastic rocks. Smaller springs issue from thin beds of 

pumice or cinders in late Tertiary (?) tuffs and agglomerates.

The ground-water conditions in the coastal plain in Departamento 

de Ahuachapan are not well known, but extensive parts of this region 

are underlain by Recent sand and gravel deposits that should yield 

moderate supplies of water to wells and springs.

LOCAL SUPPLIES 

AHUACHAPAN

The city of Ahuachapan (population about 15,000) has a watei 

supply of about 210,000 gallons of water daily, or 14 gallons per 

capita. Of the total supply approximately 150,000 gallons a day is 

raised by a centrifugal pump from Aponilla spring and 60,000 gallons 

a day is obtained by gravity through a pipeline from Los Piedrones 

springs.

Aponilla spring is about a mile east of the city. It issues from a 

ledge of jointed and fractured basaltic lava about 15 to 20 feet above 

the channel of a moderately deep ravine.

Los Piedrones springs are in the Apaneca-Santa Ana highland 

about 3 miles southeast of Ahuachapan. The springs rise in two 

groups about 1,500 feet apart along the channel of a headwater tributary of the Rio Ahuachapan. The water issues as seeps from thin 

beds of pumice and cinders within massive tuff and tuff agglomerate 

strata. The total discharge of the two spring groups is about 40 

gallons a minute.

ATIQUIZAYA

The municipal water supply of Atiquizaya (population approximately 6,000) is about 72,000 gallons a day during the rainy season 

and between 40,000 and 50,000 gallons a day in the dry season. The 

water is carried by gravity through a pipeline from Tortuguero spring. 

This spring rises in a canyon on the north slope of Cerro San Juan 

approximately 4 miles south of the city. The water issues from 

joints and fractured zones in the base of a flow of a Pleistocene andesitic lava that rests on a ledge of impermeable tuff agglomerate. The 

wet-season discharge is about 75 gallons a minute.

Within the city of Atiquizaya are many open dug wells used for 

private domestic supply. All these wells are less than 35 feet deep 

and extend only a few feet below the water table., They tap a water930754 51 6
190 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

bearing stratum of coarse cindery sand that underlies much of the 

Atiquizaya area. Three groups of springs, Ahuijuyo, El Coco, and 

Talule, issue from the same water-bearing stratum in the vicinity 

of the city. In each group the water rises in a small area of general 

seepage where open valley heads have been cut into the water-bearing 

stratum. Talule springs feed into a swampy tract lying directly 

west of the city. For malarial mosquito control the swamp has been 

artificially drained by a ramified system of open ditches which have 

an estimated total discharge of about 500 gallons a minute.

DEPARTAMENTO DE CABALAS

GENERAL FEATURES

The Departamento de Cabanas is in the north-central part of El 

Salvador and includes the northern part of the Cojutepeque highland 

district and bordering areas in the western plateau district. (See 

pi. 3.) The Cojutepeque highland within the department is underlain 

by Pleistocene and late Tertiary (?) lavas and pyroclastic rocks. 

Early (?) Tertiary volcanic and related sedimentary rocks underlie 

most of the western plateau within the department.

In the Cojutepeque highland dug wells are used to a limited extent, 

but springs are the chief source of domestic and municipal water 

supply. Numerous springs of small to moderate flow emerge in the 

headwater canyons and ravines of the Rio Jiboa, Rio Titihuapa, and 

Rio Acahuapa, and smaller streams draining north to the Rio Lempa. 

The loose or semiconsolidated Pleistocene deposits of ash and pumice 

that mantle much of the Cojutepeque highland appear to be generally 

too thin and discontinuous to sustain perennial springs in Cabanas. 

Most of the perennial springs in the highland rise from late Tertiary (?) lavas and pyroclastic rocks. Near Tejutepeque several perennial springs were observed that rise from crevices or tabular partings 

in late Tertiary (?) volcanic agglomerate or tuff. The discharges 

of these springs range from about 5 to 30 gallons a minute each. The 

springs on the Santa -Rita farm, about 1% miles west of Tejutepeque, 

are typical examples.

In Tejutepeque domestic water supplies are obtained principally 

from dug wells 20 to 30 feet deep that tap pumice lenses and partings 

in volcanic tuff and agglomerate. The yields from wells are small, 

and water levels are reported to fluctuate 5 to 10 feet during the year.

In the western plateau sections of Cabanas water supplies are obtained chiefly from small springs that rise from early (?) Tertiary 

pyroclastic rocks. The high-level springs are generally temporary 

but the springs in the deeper valleys and canyons draining to the 

Rio Lempa and Rio Titihuapa usually flow throughout the dry season.
DEPARTAMENTO DE CHALATENANGO 191

LOCAL SUPPLIES

SENSUNTEPEQUE

The city of Sensimtepeque (population about 8,000) is in the eastern part of Cabanas. The municipal distribution system supplies 

about 12,000 gallons a day which is pumped from a "captacion" 

(spring-development structure) at Catorce de Julio (Fourteenth of 

July) springs. This supply is inadequate fqr the demand, so that 

washing and bathing are done principally at El Chorro and La Mina 

springs, which have been developed and improved for local use.

Catorce de Julio springs are located about a quarter of a mile south 

of the center of the city at the head of a small open valley. The 

springs appear to issue from platy partings and vertical joints in 

dense, compact volcanic tuff. The total discharge is estimated at 

about 60 gallons a minute.

La Mina and El Chorro springs are located a quarter of a mile 

northwest and north of the city in small spring alcoves. These springs 

issue from tabular openings in volcanic tuff. La Mina spring has a 

discharge of about 50 gallons a minute, and El Chorro spring about 

25 gallons a minute.

It appears that the entire hill on which Sensuntepeque is built is 

made up of early (?) Tertiary pyroclastic rocks which in this vicinity 

are compact, fine-grained, green and red tuffs with occasional thin 

stringers of scoria and cinders. Ground water in this vicinity appears 

to move principally through crevices in these rocks. The elevations 

of Catorce de Julio, La Mina, and El Chorro springs suggest that the 

water table of the water-bearing zone that feeds the springs is about

90 feet below the surface at the Alcaldia in Sensuntepeque.

The principal segment of 

ment from Honduras in tb 

in a southwesterly direction 

ment. Smaller a^eas of the

western plateau within the

DEPARTAM3SNTO DE CHALATENANGO

The Departamento de Chalatenango lies north of the Rio Lempa 

in the northern part of El Salvador. The population is approximately 102,500. Within tie department are parts of the northern 

highlands and of the western plateau, which includes the plains of 

Chalatenango. (See pi. 3.)

the northern highlands enters the departnorthwest and parallels the Rio Lempa 

along the western margin of the departnorthern highlands occur in the northern

part of the department,, south of the Rio Sumpul. The parts of the

department include the areas adjoining

the northern highlands and the plains of Chalatenango in the south.

Within the department the northern highlands are made up of early

Tertiary volcanic rocks with related sedimentary rocks, and of Upper

Jurassic and Lower Cretacesous sandstone, shale, conglomerate, marl,
192 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

and limestone, with occasional beds of tuff and breccia, of the Metapan 

formation. Locally the Metapan formation is intruded by dikes and 

stocks of granite, granodiorite, and diorite of probable Upper Cretaceous age.

Most of the western plateau area appears to be underlain by early 

(?) Tertiary volcanic and sedimentary rocks, but the plains of Chalatenango are underlain in part by late Tertiary (?) volcanic rocks and 

Pleistocene lacustrine and alluvial deposits.

In the northern highlands and adjacent sections of the western 

plateau there are few wells, and springs are the chief source of water 

supply for domestic and municipal use. Numerous springs of small 

to moderate flow occur in the headwater canyons and ravines of 

streams draining to the Rio Lempa or the Rio Sumpul. The highleval springs usually fail early in the dry season because their contributory catchment areas are small and ground-water storage is 

limited. The lower springs in the larger and deeper valleys are 

usually perennial and sustain the dry-season flow of the streams. For 

example, the Rio Soyata, about 1% miles south of Tejutla, has a dryseason discharge of about 2 cubic feet per second, or about 900 gallons 

a minute, sustained by the aggregate flow of several small springs that 

rise from crevices and joint partings in dense, fine-grained basalt or 

andesite, which forms the country rock in this vicinity. About 2^ 

to 41/2 miles south of Tejutla several small springs along the Rio de 

Salitre that rise from partings and crevices in very dense, welded 

volcanic tuff or rhyolite have an aggregate flow of about 300 gallons 

a minute. Approximately 7 miles south of Tejutla in the valley of the 

Rio de Salitre and beside the San Salvador-Tejutla road is a dug well 

about 30 feet deep which obtains a small supply for domestic use from 

dense volcanic tuff.

Along the southern margin of the plains of Chalatenango in the 

valley of the Rio Lempa, ground-water supplies are obtained in several 

places from alluvial deposits of sand and gravel by means of wells a 

few tens of feet deep. Farther north on the plains shallow dug wells 

obtain small supplies from late Tertiary (?) pyroclastic rocks or 

Pleistocene lake-bed deposits. For example, there is a dug well 40 

feet deep beside the San Salvador-Tejutla road, about a mile north 

of the Rio Lempa, that apparently obtains water from late Tertiary 

(?) volcanic tuff.

DEPARTAMENTO DE CTJSCATLAN

GENERAL FEATURES

The Departamento de Cuscutlan, in the central part of El Salvador, 

covers an area of about 626 square miles and has approximately 100,000 

inhabitants. It includes the southwest part of the Cojutepeque highland, the extreme western part of the San Salvador highland, the vol-
DEPARTAa|lENTO DE CUSCATLAN 193

cano, Volcan Guazapa, with its surrounding eruptive field, and the 

northeastern part of the plain of Aguilares. (See pi. 3.) Pleistocene, and late Tertiary (?) lavas and pyroclastic rocks form most of 

the Cojutepeque highland, Volcan Guazapa and nearby parts of the 

San Salvador highland. The plain of Aguilares is underlain chiefly 

by Pleistocene and Recent lacustrine and alluvial deposits, which in 

turn are underlain by late TJertiary (?) volcanic rocks.

GROUNJD-WATER CONDITIONS

The rocks that compose the Cojutepeque and San Salvador highland

region of the department inc 

.and pumice, interbedded wii 

1 ava flows. The pumice anc

ude irregular beds of volcanic ash, cinders, 

h andesitic and basaltic agglomerate and 

cinder beds and the interflow zones in the

lavas are usually quite perifneable and, where present in the zone of 

saturation, yield small to ijnoderate supplies of water to wells and 

springs. In this part of the department, springs are the principal 

source of domestic and municipal water supplies, but wells are used 

to a limited extent in favorable localities.

The permanence of a spring depends principally on the size and 

extent of the ground-water intake area contributory to the spring. 

The high-level springs on tjhe upper slopes generally fail completely 

or decline in flow markedly during the season. Numerous springs of 

this type are found in the vicinity of Cojutepeque, El Carmen, and 

.San Rafael Cedros. Inhabitants of the area and travelers on the 

Pan American Highway are dependent on such springs for water 

supplies. During the dry season the shortage of water is acute, and 

water must be hauled considerable distances from more permanent 

sources. The low-level springs in the deeper canyons and valleys 

usually persist throughout |the dry season and are therefore the most 

reliable sources of water skipply in the region. A typical example 

is La Cangreja spring in the valley of the Rio Cacahuatl, about 3% 

miles south of Cojutepeque] This spring issues from scoriaceous and 

iragmental zones at the base of a lava flow and has an average discharge of about 150 gallons a minute. Other springs in this vicinity 

have similar characteristics^ though few have so large a flow.

Most of the northern half of Departamento de Cojutepeque is occupied by a segment of the plain of Aguilares. This area is underlain 

chiefly by alluvial and lacustrine deposits of water-laid tuffaceous 

silts with interbedded pumice, cinders, and occasional sand and fine 

gravel. Older volcanic agglomerates and tuffs occur in the deeper 

canyons and valleys. The! position of the water table in this area is 

controlled largely by the drainage level of the principal streams tributary to the Rio Lempa arid Rio Acelhuate. In their lower courses 

these streams are perennial, being fed in the dry season by springs 

that rise along the channel^. Spring lines, some several hundred feet
194 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

long, are commonly developed where a stream valley cuts through a 

pervious bed of pumice or cinders overlying an impermeable bed of 

tuff or agglomerate. Such spring lines are generally outcrops .of the 

regional water table and indicate the approximate position of the 

water table in the interstream areas. Usually wells in these areas 

must be dug to or below the level of these spring lines to obtain adequate supplies for domestic and stock use.

LOCAL SUPPLIES

COJUTEPEQTJE

The city of Cojutepeque (population about 7,000) has a water supply of approximately 56,000 gallons a day, or about 8 gallons per capita. All the municipal supply is obtained from spring developments 

on the Rio Cacahuatl about 3% miles south of the city. The springs 

issue from soft volcanic materials at the edge of a small alluvial valley 

about 2,000 feet below Cojutepeque. The water is delivered to the 

city by a reciprocating pump, through a 5-inch steel pipeline. The 

supply is inadequate for the needs of the city and plans have been 

made to drill a well 300 to 600 feet deep near the Pan American Highway just north of the city. Such a well should encounter one or more 

water-bearing zones in the Pleistocene or late Tertiary (?) volcanic 

rocks of the area.

EL CABMEN

The village of El Carmen (population about 200) obtains its principal water supply from the municipal spring about a quarter of a 

mile west of the town, on the Pan American Highway. The spring 

issues from a thin bed of sand in tuffaceous agglomerate. It has been 

developed by three short trenches which feed into a concrete collecting 

box and ultimately to a pila (watering trough) equipped with a spring 

valve. The discharge of the spring is about 6 g-allons a minute in the 

wet season and 4 gallons a minute in the dry season. The supply is 

considered adequate for the village.

SAN KAFAEL CEDROS

The town of San Rafael Cedros (population about 1,800) has a public water supply of approximately 75,000 gallons a day in the wet 

season, but only about 7,000 gallons a day in the dry season. The 

public supply is obtained by gravity through a 2%-inch pipeline from 

San Rafael spring, about a mile west of town. The-spring issues 

from permeable zones in a ledge of tuffaceous agglomerate. The discharge is approximately 100 gallons a minute in the wet season but 

dwindles to about 5 gallons a minute in the dry season.

In the vicinity of the town there are several small undeveloped 

springs which are used for supplemental water supply, especially in
DEPARTAMENTO DE LA LIBERTAD

The present water supply

195

the dry season. These springs issue from thin pumiceous zones in 

volcanic tuff and usually flow no more than a few gallons a minute.

of San Raf ael Cedros is not adequate.

The best solution to the problem would seem to be a drilled well, perhaps 200 to 300 feet deep, tha^, would tap one or more perennial waterbearing zones in Pleistocene or late Tertiary (?) volcanic rocks.

DEPARTAMENTO DE !LA LIBEBTAD

GENERAL FEATURES

The Departamento de La Libertad is located in the west-central 

part of El Salvador. It covers an area of about 830 square miles and 

has approximately 135,000 inhabitants. It includes the western part 

of the San Salvador highland, parts of the western plateau and most 

of the Zapotitan basin, and a part of the coastal plain. (See pi. 3.)

Within the department the San Salvador highland is underlain 

by Eecent, Pleistocene, and late Tertiary (?) pyroclastics and lavas. 

The Zapotitan basin is underlain by Pleistocene alluvial, lacustrine, 

and pyroclastic deposits. The western plateau south of the San Salvador highland is underlain 

lavas and pyroclastic rocks.

by Pleistocene and late Tertiary (?) 

The part of the coastal plain within

La Libertad department is very narrow and is underlain by rocks 

similar to those of the western plateau, covered in part by a thin veneer 

of alluvial silt, sand, and gravel.

GROTTNDJWATER CONDITIONS

In the San Salvador highland of La Libertad, springs occur extensively in the stream canyons and valleys draining the slopes of 

Volcan de San Salvador and the northern and southern slopes of the 

Cadena Costera. Springs are the principal source of water for

domestic and municipal use in this area, but wells are important

sources of water in favorable localities.

As in other parts of the republic, the permanence of a spring in 

this area depends on the size and storage capacity of the contributory 

ground-water catchment area. The high-level springs issuing from 

Recent rocks on the upper slopes of Volcan de San Salvador and in 

other parts of the highland usually fail during the dry season. 

Springs rising from older roqks at a lower elevation generally persist 

through the dry season, though usually with diminished discharge.

Most of the large springs in this highland area rise from pervious 

beds of coarse volcanic scoria or cinders and to lesser extent from 

Pleistocene andesite or basalt lava flows. Usually these rocks are 

interbedded with impermeable tuff or tuffaceous agglomerate. About 

2i/£ miles west of Nueva San Salvador on the Pan American Highway'are the springs of Los Chorros, which issue from a 5-foot stratum 

of coarse volcanic cinders lying between two massive beds of volcanic
196 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

tuff. By sapping action, a spring alcove lias been cnt almost 1,000 

feet back from the canyon of the Rio Guaramal. The discharge in 

November 1943 was estimated at about 3 cubic feet per second or 

1,350 gallons a minute. Other springs issue from the same geologic 

horizon at several points on the highway between Los Chorros and 

the village of Colon. They flowT at rates ranging from a few tens to 

a few hundred gallons a minute and are perennial.

South of the San Salvador highland, in the western plateau and 

coastal-plain districts of the department, springs most commonly rise 

from, permeable zones in tongues of Pleistocene andesitic or basaltic 

lava. The pyroclastic volcanic materials in these districts apparently 

are generally less permeable to ground water than elsewhere in the 

department. The spring of Ayagualo, about 3y2 miles south of 

Xueva San Salvador on the highway to La Libertad, is typical. It 

issues from a ledge of jointed and fractured andesite above a mass 

of impermeable volcanic agglomerate. The discharge is estimated 

at about 150 gallons a minute. Approximately a mile north of La 

Libertad on the highway to Nueva San Salvador, a well 105 feet deep 

encountered permeable water-bearing zones in andesitic lava. It is 

reported that the water is under some artesian pressure and rises to 

a static level 52 feet below the surface. The well yields 50 gallons 

a minute with only a few inches of drawdown.

The part of Departamento de La Libertad north and west of the 

San Salvador highland is occupied by the Zapotitan basin. This area 

is underlain chiefly by alluvial and lacustrine materials derived from 

the neighboring highlands. They include deposits of water-laid tuffaceous silt, pumice, and cinders with interbedcled sand and occasionally fine gravel. The pumice, cinder, sand, and gravel beds are 

generally quite permeable and are water bearing over a large part 

of the area.

In most places the water table is not deep and in some places it 

intersects the land surface, giving rise to springs, spring-fed lakes, and 

swampy tracts. Laguna de Zapotitan, at the head of the Rio Sucio, is 

a feature of this type. Approximately 2 miles southeast of the Rio 

Sucio bridge on the Pan American Highway, the water table is only 

about 10 feet below the land surface. In the well at El Recreo finca, 

approximately 2y2 miles northwest of the bridge, it was 25 feet below 

the land surface in December 1943.

In and near Quezaltepeque many wells 20 to 60 feet deep tap beds 

of water-bearing volcanic cinders interbedded with impermeable tuffaceous silt. The depth to water in these wells ranges from about 15 

to 55 feet, and water levels fluctuate 5 to 10 feet with the wet and 

dry seasons. The same water-bearing beds supply the springs of 

Poluncuilo, which rise on the side of a shallow ravine just west of
DEPARTAMENTO DE LA LIBERTAD 197

Quezaltepeque. These springs flow at the rate of about 100 gallons 

a minute.

LOCAL SUPPLIES 

ANTIGUO CTJ3CATLAN

The municipal water supplies of the village of Aiitiguo Cuscatlan 

(population 1,000) and the neighboring cantons of La Ceiba (population 1,600) and La Puerta de La Laguna (population 1,300) are 

obtained from a development of the springs of La Montana. The 

cantons of La Ceiba and La Puerta de La Laguna receive their supplies by gravity pipeline. Antiguo Cuscatlan obtains its supply by 

gravity and a booster pump. The water supplies of these villages are 

more than adequate for present requirements, but the development 

needs extensive sanitary improvements.

Directly west of Antiguo Cuscatlan is an almost circular volcanic 

sink or crater about 1,500 feet wide and 150 feet deep. The rocks 

forming the crater walls are composed of interbedded layers of highly 

permeable volcanic scoria with explosion breccia and impervious finegrained tuff. All along the south rim of the crater is an extensive 

water-bearing bed from which the springs of La Montana issue in 

permeable zones in volcanic cinders at levels ranging from the crater 

floor to about 50 feet above it. The total spring discharge from this 

bed may amount to several thousand gallons a minute.

QUEZALTEPEQUE

The city of Quezaltpeque (population 7,000) has a municipal water 

supply of approximately 32,000 gallons a day, or about 4% gallons per 

capita. Water from private wells and the springs of Poluncuilo is 

used to supplement the municipal supply, which comes from a well in 

the southern part of the city. The well is 169 feet deep and penetrates 

seven water-bearing beds in Pleistocene cinders or pumice interbedded with tuff. The water-bearing beds above 130 feet were cased 

off so that the horizons now supplying the well are below that depth. 

The static water level is approximately 52 feet below the surface, and 

the well yields 30 gallons a minute with very little drawdown.

NUEVA SAN SALVADOR (SANTA TECLA)

The city of Nueva San Salvador, formerly called Santa Tecla (estimated population about 21,000), is supplied with approximately 

400,000 gallons of water daily, or about 19 gallons per capita. The 

supplies are obtained from a series of nine small spring developments, 

a pumping plant at the springs of Ayagualo, and a deep well near the 

northern edge of the city.

Of the total supply approximately 100,000 gallons a day is delivered by gravity through pipelines from the nine spring developments
198 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

located in the hills southwest of Nueva San Salvador. Two of the 

springs, San Andres and Loma Larga, issue from tabular partings 

in Pleistocene or late Tertiary (?) andesite lava flows interbedded in 

massive tuff. These springs contribute most of the gravity supply of 

the city. The remaining seven springs contribute almost negligible 

flows. They issue at relatively high elevation from thin permeable 

lenses of pumice in massive impermeable tuff. In the dry season four 

of the springs fail completely, and the remaining three supply less 

than 3 gallons a minute to the gravity system.

A pumping plant at the spring of Ayagualo supplies approximately 

170,000 gallons a day to Nueva San Salvador. The water is raised 

by pumping some 670 feet above the spring development to a 300,000- 

gallon storage tank, and from there it is delivered by gravity pipeline 

to the city.

A deep well on the Larreynaga finca at the northern outskirts of 

Nueva San Salvador furnishes about 130,000 gallons a day to the 

city supply. The well was completed in May 1942 at a depth of 630 

feet. The static water level is reported to be about 513 feet below the 

land surface. An 11-stage, 8-inch turbine pump set in the well produces 330 gallons a minute with a drawdown of 26 feet in the water 

level. The water-bearing beds supplying the well lie between 545 

and 572 feet below the surface. These beds appear to be in volcanic 

scoria or sand interbedded with basaltic lava flows, tuff, and ash beds 

of Pleistocene or late Tertiary (?) age. The well was improperly 

constructed and poorly developed when completed; as a result the 

pumping equipment has operated inefficiently and the withdrawal is 

much less than the potential yield.

The present water supply of Nueva San Salvador is inadequate for 

the needs and future growth of the city. It has been recommended 

that a new well be drilled in the lower part of the city to obtain additional water. Such a well would need to be between 500 and 600 feet 

deep in order to tap the water-bearing beds that supply the Larreynaga 

well. If the well is properly alined, constructed, developed, and 

equipped, an adequate supply for the present and immediate future 

needs of the city can be obtained.

I>EPARTAMENTO DE LA PAZ

GENERAL FEATURES

The Departamento de La Paz is in the south-central part of El 

Salvador. It has an area of approximately 895 square miles and has 

a population of about 99,000. The department includes the eastern 

extension of the San Salvador highland south of Laguna de Ilopango, 

the southern half of the San Vicente highland, a part of the western 

plateau south of the highland areas, and a broad segment of the coastal 

plain. (See pi. 3.)
DEPARTAMENTO DE LA PAZ 199

Within the department the San Salvador highland is coextensive 

with the Cadena Costera of El Salvador. Together with the western 

plateau and the inland margin of the coastal plain, it is made up 

largely of late Tertiary (?) pyroclastic rocks and lava flows. The 

San Vicente highland is underlain principally by Recent and Pleistocene volcanic rocks. The seaward margin of the coastal plain is underlain chiefly by Recent and Pleistocene alluvial deposits, but in places 

late Tertiary (?) rocks crop out from beneath the alluvial cover.

GROUND-WATER CONDITIONS

The rocks that compose the San Salvador highland and the western 

plateau with adjacent parts of the coastal plain include late Tertiary 

(?) tuffs, tuffaceous clays, and compact andesitic agglomerates with 

occasional intercalated basalt and andesite lava flows.

The tuffs and clays are largely impermeable and hence yield little 

water to wells and springs. The agglomerates are somewhat more 

permeable, and where present in the zone of saturation they furnish 

small to moderate quantities of water to wells and springs from joints 

and other secondary partings in the rock. Shallow dug domestic wells 

in and near Santiago and Zacatecoluca obtain water supplies from 

this source.

Permeable zones in lava flows interbeclded with the pyroclastic 

materials yield moderate to abundant supplies to wells and springs 

where present in the zone of saturation. In the vicinity of Zacatecoluca 

are several small springs and two large spring groups that apparently 

rise from bouldery deposits, probably formed from broken or highly 

jointed andesite lava flows that are interbedded with volcanic agglomerate and tuff. One of the spring groups, Santa Irene, about l1/^ 

miles southwest of Zacatecoluca discharges at a rate of approximately 

3,000 gallons a minute. The group includes one major and three 

minor springs that rise within a few score feet of one another. About 

a mile south of the city is the spring group of Inchanmichen, quite 

similar to that of Santa Irene. The Inchanmichen springs discharge 

roughly 2,500 gallons a minute and are used to generate power at a 

small hydroelectric plant.

The alluvial deposits that mantle much of the coastal plain thicken 

toward the coast and finally merge with estuarine clay, silt, and beach 

sand near the shore line. Along the lower reaches of the Rio Jiboa, 

the Rio Amate, and other smaller streams that flow southwest across 

the coastal plain to the ocean, there are extensive deposits of sand 

and fine gravel that yield moderate to large supplies of water to wells 

at shallow depth. On a narrow barrier beach that extends along the 

shore of La Paz for about 10 miles near Estero Grande de Jaltepeque, 

small fishing communities and beach resorts obtain small domestic 

water supplies from shallow wells dug in beach sand. The water
200 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

becomes somewhat saline in the dry season because of insufficient 

fresh-water recharge from rain to replace ground water dissipated by 

springs at the shore.

LOCAL SUPPLIES

ZACATECOLUCA

The city of Zacatecoluca, with a population of approximately 10,000, 

has a public water supply of approximately 70,000 gallons a day or 

7 gallons per capita. About half the city supply is delivered through 

a gravity pipeline from four collecting boxes at the springs of 

Apantes. The rest of the city supply is obtained from a well in the 

northern outskirts of the city. The springs of Apantes are about 5 

miles northeast of the city. They issue from tabular partings in 

tuffaceous agglomerate and thin lenses of cinders interbedded with 

volcanic tuff. The discharge has declined since the spring developments were made in 1940, a condition which probably has been brought 

about by a cycle of dry years.

The municipal well of Zacatecoluca is approximately 400 feet deep 

and is cased to the bottom with 8-inch casing. The water level is 

about 325 feet below the land surface. The wTell is equipped with a 

reciprocating pump powered by a Diesel engine that delivers 60 

gallons a minute for 9 hours a day.

The existing water supply of Zacatecoluca is inadequate, and a new 

source of water is needed. An adequate supply could be obtained 

from a well drilled near the present storage tanks to a depth of about 

400 feet. The necessary depth of a well drilled down the slope near 

the center of town would be considerably less. The springs of Inchanmichen and Santa Irene and the municipal well indicate that there 

is an extensive water-bearing bed beneath the city. One or two properly constructed wells completed in this bed and fitted with modern 

pumping equipment could adequately supply water for the city.

DEPARTAMENTO DE LA UNION

GENERAL FEATURES

The Departamento de La Union includes all of the extreme eastern 

part of El Salvador. It covers about 860 square miles and has approximately 94,500 inhabitants. The northern half of the department is 

included in the eastern upland and the southern part in the coastal 

plain. (See pi. 3.)

Most of the eastern upland in Departamento de La Union is a moderately dissected hilly region with a wT ell-integrated drainage pattern. 

The area is underlain principally by lava and pyroclastic rocks probably of early (?) Tertiary age, with thin alluvial deposits of sand 

and gravel in the principal stream valleys.

The coastal plain in the department is underlain by late Tertiary (?)
DEPARTAMENTO DE LA UNION 201

volcanic rocks that are mantled by Pleistocene and Kecent alluvial 

deposits of silt, sand, and gravel derived from the upland areas. 

Rising above the coastal plain south of the city of La Union is Volcan 

Conchagua (elevation 4,100 feet). The volcano and the immediate 

surrounding area are composed of Eeeent and Pleistocene pyroclastic 

materials and lava flows.

GROUND-WATER CONDITIONS

The rocks that underlie the eastern, upland and adjacent areas of 

the coastal plain include weathered lavas of andesite and basalt with 

associated siliceous lavas of Tertiary age. These rocks are intercalated with pyroclastic tuffs and agglomerates and, occasionally, 

detrital sandstones and conglomerates. The permeability of the volcanic rocks is generally lower than that of similar rocks of younger 

age. In many areas their initial permeability has been reduced by 

weathering and induration. However, in many areas water stored 

in tabular openings and fragmental zones sustains small springs and 

supplies wells of small to moderate yield.

About 3 miles west of Santa Eosa on the highway to San Miguel are 

the springs of El Jicaro. They issue from fractures and tabular partings in dense, altered tuffaceous agglomerate in a zone about 75 feet 

long. The spring has been improved through development by a covered cut-off trench and collecting box, which delivers about 30 gallons 

a minute to a roadside watering place for travelers.

In the vicinity of the canton of Albornoz on the highway about 4% 

miles west of Santa Eosa, dug wells 30 to 50 feet deep obtain small 

domestic supplies from joint or fracture partings in volcanic tuff or 

andesite. The water table at these wells is reported to fluctuate annually through a range of 15 to 20 feet with seasonal variations in 

rainfall.

Over much of the coastal plain, alluvial sand and gravel deposits 

yield moderate to large supplies to shallow wells. The water table 

is not deep in most of the area and in places is at the land surface, 

giving rise to swampy tracts and springs such as those near Laguna 

del: Camalotal. Where the alluvial deposits are above the zone of 

saturation, small to moderate supplies of water are obtained from 

wells in the underlying Tertiary volcanic rocks.

LOCAL SUPPLIES

SANTA ROSA

The town of Santa Eosa (estimated population 5,500) has a public' 

water supply of approximately 30,000 gallons a day or about 6 gallons 

per capita. The town supply is delivered by gravity pipeline from 

two springs, La Chorrera and Las Anonas, about 2 miles southwest of 

town.
202 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

The springs are about a quarter of a mile apart on the flank of a 

ridge. The water issues from tabular partings in fractured andesite 

lava overlying tuffaceous agglomerate. The discharge of La Chorrera 

is about 20 gallons a minute and that of Las Anonas about 5 gallons a 

minute.

In Santa Rosa and vicinity are numerous dug wells ranging in depth 

from 25 to 55 feet. The water-bearing bed is in volcanic tuff or tuffaceous agglomerate, which yields only small to moderate supplies of 

water to wells. Water levels jn these wells are reported to fluctuate 

10 to 15 feet through the annual wet-dry cycle.

DEPARTAMENTO DE MORAZAN

GENERAL FEATURES

The Departamento de Morazan, in the northeastern part of El Salvador, covers an area of approximately 895 square miles and has about 

88,000 inhabitants. With the exception of a small segment of the 

northern highlands, all of the department is included in the eastern 

upland. (See pi. 3.)

GROUND-WATER CONDITIONS

Most of Morazan is a moderately dissected hilly to mountainous upland whose relief increases gradually from south to north. The surface drainage is well integrated in the Rio Torola, the Rio San Miguel, 

and their tributaries. The principal rocks of the upland area are 

interbedded pyroclastic and flow rocks of probable early (?) Tertiary 

age. Andesites with basalt are common rock types but siliceous rocks 

occur locally. Rhyolite and dacite lava flows interbedded with pyroclastic rocks were observed by the writers at various points along the 

highway 3 to 4 miles northeast of Jocoro, as well as in other scattered 

localities in the department.

Generally the early (?) Tertiary rocks in the department yield only, 

small or moderate supplies of water to wells and springs. At Jocoro 

and in the vicinity several domestic dug wells 15 to 25 feet deep yield 

small supplies from a water-bearing zone in dense tuff or tuffaceous 

agglomerate. The water table at these wells is reported to fluctuate 

only a few feet through the annual wet-dry cycle.

In San Carlos moderate water supplies are obtained from dug wells 

30 to 35 feet deep. The water-bearing bed is apparently in tabular 

openings in dense tuff or tuff breccia. About half a mile west of the 

village on a low ridge two small springs issue from crevices in an 

'andesitic lava flow overlying dense tuff. Each of the springs discharges about 4 gallons a minute and is reported to flow throughout 

the year.

In the northern highland area of Morazan sedimentary rocks of
DEPARTAMENO DE MORAZAN 203

probable Jurassic and Cretaceous age are reported to occur. This 

area was not examined by the writers, and no comment can be made 

regarding the water-bearing properties of the rocks in that area.

LOCAL SUPPLIES 

JOCOBO

The town of Jocoro (population approximately 2,000) has a public 

water supply of approximately 86,000 gallons a day or 43 gallons per 

capita. The supply is delivered by gravity pipeline from the springs 

of El Pital. The springs are in a deep canyon about 1% miles southeast of the town. They issue from fractures in a ledge of volcanic 

breccia. The combined flow from the three springs was estimated to 

be 60 gallons a minute.

The present supply is entirely adequate for the needs of the town, 

but the sanitary quality of the water could be greatly improved by a 

few small repairs in the spring-development structures.

SAN FRANCISCO

The city of San Francisco (population 6,000) obtains its water from 

two sources: Chilanga spring, about 3 miles north-northwest of the 

town, and a subsurface diversion of underflow in the channel of the 

Rio Agua Fria, about 1^ miles north-northeast.

The existing supply is inadequate for the present and immediate 

future needs of the city. The supply furnished by the Agua Fria system could perhaps be doubled by developing the springs that feed the 

Rio Agua Fria.

Supplemental water supplies in and near the city are obtained from 

dug wells 25 to 35 feet deep. The water in these wells appears to issue 

from crevices in dense volcanic tuff. Water levels are reported to 

fluctuate 10 to 15 feet through the annual wet-dry cycle.

DEPARTAMENTO DE SAN MIGUEL

GENERAL FEATURES

The Departamento de San Miguel is in the eastern part of El Salvador and covers an area of approximately 1,325 square miles. It has 

about 150,000 inhabitants. Within the boundaries of the department 

are Volcan de San Miguel, a part of the eastern upland, a part of the 

coastal plain, and the Colinas de Jucuaran. (See pi. 3.)

The eastern upland areas are underlain chiefly by sedimentary and 

volcanic rocks of probable early (?) Tertiary age. Volcan de San 

Miguel and the area immediately surrounding it are underlain by Recent and Pleistocene volcanic rocks. The coastal plain is mantled by 

Recent and Pleistocene alluvial deposits but is underlain by late 

Tertiary (?) volcanic rocks, which also make up most of the Colinas de 

Jucuaran.
204 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA 

GROUND-WATER CONDITIONS

The rocks underlying the eastern upland region in the northern part 

of the department include a somewhat heterogeneous assemblage of 

pyroclastic materials interbedded with andesitic and siliceous lava 

flows, conglomerates, laminated clays, and carbonaceous beds. Most 

of these rocks are well indurated or altered by weathering. As a 

result, initial openings in the rocks have been largely destroyed and 

their capacity to transmit warer has been considerably reduced. However, numerous small springs in this area, especially in the valleys of 

the tributaries of the Bio Chapeltique, issue principally from joint 

partings or fracture zones in dense pryoclastic rocks or lava flows.

In Chapeltique and vicinity fracture and joint openings in dense 

tuffaceous agglomerate yield small domestic supplies to dug wells 20 

to 30 feet deep. Water levels in these wells fluctuate as much as 10 to 

15 feet with seasonal rainfall distribution. Similar ground-water conditions are found in the lowland areas between Chapeltique and 

Moncagua.

Near San Miguel the coastal plain merges gradually with the eastern 

upland. Much of the coastal plain is mantled by alluvial deposits 

of silt, sand, and gravel derived from adjacent higher areas of volcanic 

rock. The water table is fairly shallow and water is found in saturated 

sand and gravel of the alluvial deposits over much of the coastal 

plain. In places the water table intersects the land surface, giving 

rise to swampy tracts and shallow spring-fed lakes. In the vicinity 

of San Miguel many large springs rise in swampy tracts from the 

water-bearing beds of sand or water-laid cinders. Numerous dug 

wells 20 to 40 feet deep obtain domestic supplies from this source.

The Colinas de Jucuaran, which parallel the coast line of Departamento de San Miguel, are composed chiefly of clayey agglomerates 

intercalated with basalt and andesite lava flows. Most of the springs 

observed in this area issue from joint partings in the lava flows.

In Chirilagua all domestic water supplies are obtained from dug 

wells 35 to 45 feet deep. The wells, on the west side of the town, obtain 

supplies from water-bearing zones in tuffaceous agglomerate. Water 

levels in the wells are reported to fluctuate 10 to 15 feet annually. In 

the center of the town is an andesitic lava flow overlain by the tuffaceous agglomerate. The water-bearing zone in the agglomerate on 

the west side of town apparently does not extend eastward, as a holedug in the plaza to a depth of 155 feet penetrated andesitic lava for 

its entire depth.

DEPARTAMENTO DE SAN SALVADOR

GENERAL FEATURES

The Departamento de San Salvador lies in the central part of El 

Salvador. It covers about 780 square miles and has 207,000 inhabit-
DEPARTAMENTO DE LA SALVADOR 205

ants. Within the department are included the central part of the 

San Salvador highland, part of the plain of Aguilares and the contiguous Zapotitan basin, and a small part of the western plateau. 

(See pi. 3.)

The San Salvador highland and the western plateau to the south 

are underlain chiefly by Pleistocene and late Tertiary (?) pyroclastic 

rocks and lava flows. The plain of Aguilares and the Zapotitan basin 

Are mantled by Pleistocene alluvial and lacustrine deposits which rest 

on late Tertiary (?) volcanic rocks.

GROUND-WATER CONDITIONS

The San Salvador highland and the western plateau are made up 

of a heterogeneous assemblage of volcanic rocks formed by both explosive and liquid eruptions. The explosive rock types include extensive 

beds of tuff, pumice, cinders, agglomerate, and breccia. Intercalated 

with these are scattered flows of basalt and andesite lava.

The pumice and cinder beds are productive water bearers where 

present in the zone of saturation. The scoriaceous and fragmental 

facies of the lava flows are quite permeable and supply many wells 

and springs in the department. Typical examples of such wells and 

springs occur near Panchimalco, Mejicanos, San Martin, and Prusia.

About half a mile southeast of Panchimalco are Cataracta springs, 

which issue near the bottom of an alcove or box canyon formed by 

the recession of a waterfall of the Rio Cuitapan. The springs issue 

from joints and fractures in an andesite lava flow above impermeable 

volcanic tuff, in a zone about 50 feet long. The discharge of the 

springs, estimated at 1,200 gallons a minute, is sustained throughout 

the year. About half a mile west of 'Panchimalco are San Roman 

springs, which issue on a hill slope to form a small stream that flows 

south toward the Pacific. The springs issue from volcanic sand or 

cinders overlying agglomerate in two adjacent cup-shaped depressions. The combined flow of the two springs was estimated to be 

500 gallons a minute.

About half a mile southeast of Mejicanos (a suburb of San Salvador) are the springs of El Borbollon which rise in the ravine of Rio 

Borbollon, a tributary of Rio Acelhuate. The springs issue from a 

permeable zone in broken and fragmental basaltic lava beneath a 

bed of tuffaceous agglomerate. The discharge is estimated to be about 

1,500 gallons a minute.

In the vicinity of San Martin an extensive water-bearing horizon 

occurs at the base of a highly permeable pumice stratum that overlies 

an impermeable stratum of volcanic tuff. Numerous spring lines occur 

where canyons and valleys of the areas are cut below this contact. 

Typical examples in the vicinity of San Martin are Don Jose springs, 

2 miles northeast, Ayalapa spring, 2 miles north, and numerous small
206 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

springs along the Arenal Colochos. It has been estiiriated that this 

water-bearing bed is about 250 to 300 feet below the surface at San. 

Martin.

In the vicinity of Prusia one or more water-bearing beds occur from 

60 to 200 feet below the surface in strata of highly permeable volcanic 

sand or pumice interbedded with tuff. These beds are tapped by the 

well of the San Salvador municipal slaughterhouse, that of the Prusia 

mill, and other wells. Yields ranging from 75 to 200 gallons a minute 

are obtained from wells drawing upon these water-bearing strata.

The plain of Aguilares and the adjacent Zapotitan basin in the 

northern part of the department are underlain by alluvial and lacustrine deposits of water-laid tuffaceous clay, silt, and sand, with some 

gravel. These deposits are in turn underlain by late Tertiary (?) 

volcanic rocks.

In the vicinity of Guazapa dug wells less than 100 feet deep obtain 

domestic supplies from alluvial or lacustrine deposits and the underlying volcanic rocks. Small springs that issue from permeable beds 

in the alluvial deposits occur at several points near the San SalvadorTejutla road 4 to 5 miles south of the Rio Lempa.

LOCAL SUPPLIES

SAN SALVADOE

The city of San Salvador (population 104,000) has a water supply 

of approximately 9 million gallons a day, or 86 gallons per capita. 

These supplies are obtained from five wells widely spaced throughout 

the city, from a pumping plant at El Coro springs, and from four pipelines that deliver by gravity the flow of 20 developed springs. Of the 

total daily supply about 2,640,000 gallons is obtained from the five 

wells, about 3,170,000 gallons from the pumping plant at El Coro, and 

about 3,195,000 gallons by gravity from the 20 springs.

The municipal wells and numerous private wells obtain supplies 

from water-bearing zones in an extensive bed of basaltic lava that 

underlies most of San Salvador. Just east of the city this bed crops 

out along the canyon of the Rio Acelhuate in the vicinity of El Coro 

and La Chacra. Beneath the city the lava bed is overlain by younger 

pyroclastic materials that include tuff, agglomerate, cinders, and explosion breccia. These materials range in thickness from about 30 

feet in the eastern part of the city to about 250 feet at the west end of 

the city.

The principal water-bearing bed tapped by wells in the city is 

apparently in the upper part of the lava bed. This stratum is full of 

cavernous openings, contraction partings, and scoriaceous material, 

which in the aggregate contain a considerable volume of water. The 

municipal wells, which are 205 to 370 feet deep, yield 300 to 600 gallons
DEPARTAMENTO DE LA SALVADOR 207

a minute each from this stratum. Several springs that issue from the 

lava bed in its line of outcrop along the Kio Acelhuate yield several 

hundred gallons a minute. La Chacra and El Coro, from which part 

of the municipal water supply is pumped, are the largest and most 

important of these springs.

The gravity water supply of San Salvador is obtained from 

developed springs that rise in the ravines of headwater tributaries of 

the Rio Acelhuate south of the city. The springs of Ilohuapa, about 

3 miles south of the city, rise in three adjacent spring heads from a 

stratum of pumice or cinders interbedded with volcanic tuff. The 

total flow of these springs is about 200 gallons a minute.

In a canyon on the southern outskirts of San Salvador is the spring 

of Monserrat, which issues from crevices and cavities in the upper 

part of a lava flow and contributes about 30 gallons a minute to the 

city supply.

Las Dantas springs are located along the canyon of the Rio Acelhuate from 1 to 2 miles south of San Salvador. In all, three groups 

of springs, which in successive order upstream are Danta Vieja, 

Fuentes Intermedias, and Danta Nueva, have been developed.

The springs of Danta Vieja issue from crevices in a fractured, 

blocky bed of andesitic or basaltic lava at the base of a gentle slope 

adjacent to the Rio Acelhuate. About a quarter of a mile upstream 

from Danta Vieja are the springs Fuentes Intermedias. Several 

small springs in the group issue from scoriaceous or fragmental zones 

in one or more flows of andesitic lava at levels 20 to 150 feet above the 

channel of the river. The springs of Danta Nueva also issue from 

an extensive fractured zone in an andesitic lava flow. These springs 

rise along the channel of the river about a mile upstream from Danta 

Vieja. The total contribution of the spring developments of Las 

Dantas to the water supply of San Salvador is approximately 2,000 

gallons a minute.

MEJICANOS

The city of Mejicanos, about iy2 miles north of San Salvador, has an 

estimated population of 8,000. The municipal water supply is about 

17,300 gallons a day or an average of only 2 gallons per capita. The 

supply is obtained from La Bomba spring, in a small ravine about a 

quarter of a mile northeast of the city hall. The spring issues from 

a thin stratum of scoria or pumice interbedded with dense volcanic 

tuff. It flows at a rate of about 18 gallons a minute. During part of 

the day this flow is delivered direct to the city distribution system 

by a small reciprocating pump. During the rest of the day the spring 

flows to waste for lack of storage facilities at the spring or in the city.

Within Mejicanos numerous private dug wells furnish small domestic water supplies that supplement the inadequate municipal supply.
208 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

These wells range in depth from about 75 feet in the central part to 

about 125 feet in the higher western part of the city. Most of the-wells 

in the central and northern parts of the city tap a water-bearing, bed 

of volcanic pumice or cinders 75 to 95 feet below the surface. The 

springs of La Bomba apparently rise from the same water-bearing 

zone. The Chacon well in the western part of the city taps a deeper 

water-bearing zone at a depth of 125 feet in scoriaceous basalt, apparently in the upper part of a lava flow. This may be the same zone as 

that supplying the springs of El Borbollon southeast of Mejicanos. 

The existing wells and springs indicate the presence of one or more 

extensive water-bearing zones at depths of less than 200 feet beneath 

the city. An adequate water supply for Mejicanos could be obtained 

from one or two drilled wells finished and properly developed in these 

zones and furnished with efficient pumping equipment.

VILLA DELGADO

The city of Villa Delgado, about 2 miles east of San Salvador, has 

a population of about 10,000. It has a public water supply of approximately 70,000 gallons a day or about 7 gallons per capita. An infiltration tunnel at the springs of La Bomba is the source of the municipal 

supply. Two small reciprocating pumps raise water from the springs 

to a 7,000-gallon distribution tank, in the higher part of the city. The 

springs of La Bomba issue from a bed of pumice aBove a layer of 

volcanic tuff in a tributary ravine of the Rio Urbina in the northern 

outskirts of the city. The springs discharge at a rate of about 100 

gallons a minute. In the suburb of Paleca are many dug wells that 

obtain small domestic supplies from water-bearing volcanic sand or 

pumice at depths ranging from 100 to 125 feet below the surface.

The springs along the Kio Urbina and the wells in Paleca indicate 

that one or more water-bearing beds occur beneath much of Villa 

Delgado at depths of less than 200 feet. One or two drilled wells 

finished and properly developed in these beds and equipped with efficient pumps could furnish the present and immediate future water 

requirements of the city.

SAN MARTIN

The town of San Martin (estimated population 5,000) has a public 

water supply of about 30,000 gallons daily, or about 6 gallons per 

capita. The supply is obtained by gravity pipeline from captations 

on three springs about 5 miles west of the town. The springs issue 

from a short lens of pumice interbedded with massive, impermeable 

volcanic tuff. They have a total flow in the wet season of about 20 

gallons a minute but in the dry season perhaps only half that amount. 

As mentioned in the general discussion on ground-water conditions 

in the Departamento de San Salvador, there is believed to be an ex-
DEPARTAMENTO DE SAN VICENTE 209

tensive water-bearing zone about 250 to 300 feet below the surface 

at San Martin. One well properly developed and finished in this zone 

and equipped with an efficient pump could furnish the town with an 

adequate water supply.

TONACATEPEQUE

The town of Tonacatepeque (population about 3,000) has a public 

water supply of about 43,000 gallons a day, or about 14 gallons per 

capita. The supply is delivered by gravity pipeline to the town from 

La Fuente spring, which is about 2% miles southeast of the town on a 

hill slope adjacent to a waterfall of the Rio Izmatapa. The spring 

issues from the base of a platy flow of andesitic lava that is overlain 

by flow breccia and underlain by volcanic tuff with lenses of pumice. 

The flow is about 30 gallons a minute in the wet season and somewhat 

less in the dry season.

About iy2 miles south of Tonacatepeque are the springs of Los 

Chorros, which discharge about 75 gallons a minute. Additional 

water supplies for the town could be obtained through gravity pipeline 

by development of these springs.

DEPARTAMENTO DE SAN VICENTE *

GENERAL FEATURES

The Departamento de San Vicente lies in the central part of El Salvador. It has an area of about 870 square miles and a population 

of about 90,000. The department covers a part of the western plateau 

with a contiguous segment of the Cojutepeque highland, the northern 

part of the San Vicente highland, and a part of the coastal plain 

including the lower valley of the Rio Lempa. (See pi. 3.)

Within the department the western plateau is underlain chiefly by 

late Tertiary (?) pyroclastic rocks with interbedded lava flows. 

Pleistocene volcanic rocks underlie much of the Cojutepeque highland and limited areas of the western plateau. The San Vicente highland is underlain by Pleistocene and Recent volcanic rocks. The seaward margin of the coastal plain and the lower valley of the Rio 

Lempa are underlain chiefly by Recent and Pleistocene alluvial deposits, but in many places late Tertiary (?) rocks crop out from 

beneath the alluvial cover.

GROUND-WATER CONDITIONS

The late Tertiary (?) rocks that constitute the western plateau of 

Departamento de San Vicente include a heterogeneous assortment of 

volcanic breccias, agglomerates, and tuffs with occasional interbedded 

lava flows, In the Cojutepeque highland and limited areas of the 

western plateau, tKese rocks are overlain by soft or semiconsolidated 

ash and pumice deposits of probable Pleistocene age.
210 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

The tuffs, agglomerates, and breccias are not generally permeable 

and hence yield only meager supplies of water to wells and springs. 

The strata of pumice and cinders and the scoriaceous and f ragmental 

zones in the lava flows are important aquifers where present in the 

zone of saturation.

As in other parts of the republic, most of the high-level springs 

issuing from these rocks fail in the dry season, but most springs at 

lower elevation have greater catchment areas and are perennial. In 

the vicinity of Santo Domingo, for example, numerous small springs 

issue from thin lenses of pumice "interbedded with volcanic ash. 

Most of these fail in the dry season, but a few, such as Encuentras 

spring about half a mile north-northeast of town, flow throughout 

the dry season. This spring discharges about 2 gallons a minute and 

is the principal source of drinking water for the people of Santo 

Domingo.

Southeastward along the Pan American Highway from kilometer 

45 at Santo Domingo to kilometer 60, perennial springs are rare, and 

those that.persist through the dry season become increasingly important despite their small yields and relative inaccessibility. A typical 

example is La Leona spring, which issues 011 a steep slope about 600 

feet north of the highway at kilometer 54 and about 2 miles southwest 

of San Esteban. The spring issues from a fractured zone in a flow 

of vitreous lava that is interbedded with volcanic agglomerate and 

tuff. A flow of about 3 gallons a minute is sustained throughout the 

dry season and provides water for rural inhabitants of the area and 

travelers on the highway. Another example is Petaca spring, about 

600 feet north of the highway at kilometer 56!/2- This spring issues 

from tabular partings in a ledge of dense volcanic agglomerate sind 

discharges about 2 gallons a minute.

Between kilometer 60 and kilometer 62 the Pan American Highway 

crosses the basin of Laguna Apastepeque. In this area the water 

table is generally less than 50 feet below the surface, and numerous 

small springs feed into Laguna Apastepeque, Laguna Ciego, Bio 

Izmatapa, and other small streams of the area. The water-bearing 

beds beneath this basin occur in beds of volcanic sand or cinders interbedded with ash or tuff.

Between kilometer 62 and kilometer 80 along the highway perennial 

springs occur only infrequently. Near kilometer 6&y2 is the spring 

of El Carrizo, which issues from a blocky andesitic lava flow overlying a bed of dense clayey tuff. The dry-season flow is about 5 

gallons a minute. At kilometer 78*4 the highway crosses the Quebrada 

Seca. About a quarter of a mile upstream from this crossing several 

springs issue from permeable zones in an extensive flow of andesite 

lava. These springs flow at rates ranging from about 5 to 15 gallons a 

minute and persist throughout the dry season.
DEPARTAMENTO DE SAN VICENTE 211

In most of the coastal plain and the, lower Eio Lempa valley the 

vrater table is not far below the surface. Near the coast and along 

the Rio Lempa extensive swampy tracts are fed by ground-water discharge, and in the adjoining areas the water table occurs at depths of 

a few feet to a few tens of feet. Shallow dug wells are the principal 

source of domestic and public water supplies in this region. The 

wells tap water-bearing zones in alluvial deposits of sand and gravel 

or, where these are thin or absent, in the underlying late Tertiary (?) 

Tolcanic rocks.

The San Vicente highland is made up of pyroclastic tuffs, agglomerates, 'and breccias interbedded with andesitic and basaltic lava flows. 

The pumice and cinder beds in the pyroclastic materials and the f ragmental and scoriaceous zones in the lava flows are quite permeable and 

yield moderate supplies of water to wells and springs. Locally 

permeable sand and gravel deposits are found in alluvial fans around 

the base of Volcan Chichontepec. Where these are in the zone of 

saturation, they yield small to moderate supplies to wells and springs.

About a quarter of a mile north of Tepetitan numerous small springs 

issue from a saturated zone in sand and gravel in the channel of the 

Quebrada del Blanco, a tributary of Eio Acahuapa. The aggregate 

discharge of the springs is about 100 gallons a minute a few hundred 

feet below the uppermost spring head. In this same vicinity are the 

springs of El Almendro, which issue from a thin bed of pumice 

between beds of volcanic ash. The springs flow at the rate of about 

25 gallons a minute.

Just west of the town of Verapaz are the springs of Verapaz. The 

springs issue from an extensive saturated zone a few hundred feet 

long on the east bank of the stream channel. The saturated zone occurs in a bed of sand and gravel lying between beds of volcanic ash. 

The aggregate flow of the springs about 200 feet below the uppermost 

spring head is approximately 150 gallons a minute. In the town of 

Yerapaz dug domestic wells 60 to 75 feet deep obtain supplies from 

beds of pumice or volcanic sand interbedded with ash or agglomerate.

The springs of San Cayetano, about 2 miles west of San Vicente, 

rise in a small spring basin from a bed of cinders or sand interbedded 

with ash. The flow of the springs is about 100 gallons a minute in 

the wet season but diminishes to about 50 gallons a minute in the 

dry season. Near the village of Ixtepeque are the springs of El 

Zapote, whose origin and occurrence are similar to those of San 

Cayetano. These springs discharge about 150 gallons a minute.

LOCAL SUPPLIES

GTTADALUPE

The town of Guadalupe (population 4,000) has a public water supply of approximately 14,000 gallons a day in the wet season and about
212 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

3,500 gallons a day in the dry, season. This is equivalent to an available supply of about 3 gallons per capita in the wet season and less 

than 1 gallon per capita in the dry season. The public supply is 

delivered by gravity pipeline from El Pinar spring, about 2 miles 

east of town on the slope of San Vicente volcano.

This supply is hardly sufficient in the wet season and almost fails 

entirely in the dry season. To alleviate the water shortage a well 

315 feet deep has recently been dug by the Department of Public 

Works. The water-bearing zone, at the bottom of the well, consists 

of scoriaceous material about 6 feet thick beneath a dense basaltic 

lava flow 30 feet thick. The materials removed from the well above 

the lava flow are chiefly volcanic tuff, agglomerate, and pumice. This 

well will furnish an adequate water supply for Guadalupe if it is 

properly developed, completed, and fitted with an efficient pump.

SAN VICENTE

The city of San Vicente (population 12.500) has a water supply 

of approximately 280,000 gallons a day or about 22 gallons a day per 

capita. The supply is delivered by gravity pipelines from the springs 

of El Cubo, La Quinta, and Agua Caliente. The spring of El Cubo, 

about 2 miles southwest of San Vicente, issues from tabular partings 

in tuffaceous agglomerate. The flow is estimated to be about 25 gallons a minute. La Quinta springs, about 1^ miles west of the city, 

issue from two orifices in tabular partings in volcanic flow breccia. 

These springs discharge about 75 gallons a minute. The principal 

source of municipal water is Agua Caliente spring, about half a mile 

south of the city. The spring issues from tabular partings in a bed 

of platy lava and discharges about 100 gallons a minute.

DEPARTAMENTO DE SANTA ANA 

GENERAL FEATURES

The Departamento de Santa Ana, in the northwestern part of El Salvador (pi. 3), covers an area of about 1,350 square miles and has a 

population of approximately 180,000. Within the department are 

included the central and eastern parts of the Apaneca-Santa Ana highland, a part of the northern highlands, a part of the western plateau 

with adjacent sections of the Zapotitan basin, and the plain of Candelaria. (See pi. 3.)

The rocks of the Apaneca-Santa Ana highland are chiefly Recent, 

Pleistocene, and late Tertiary (?) pyroclastic materials and lava flows. 

The area near Lago de Giiija, the plain of Candelaria, and the 

Zapotitan basin are underlain chiefly by alluvial and lacustrine deposits of silt, sand, and clay of Pleistocene age. In many places, 

however,' they are underlain by late Tertiary (?) volcanics or interbedded with Pleistocene volcanic rocks. The rocks of the northern
DEPARTAMENTO DE SANTA ANA 213

highland belong to the Metapan formation and early (?) Tertiary 

volcanic and sedimentary rocks.

GROUND-WATER CONDITIONS

In the Apaneca-Santa Ana highland springs are the principal 

source of domestic and municipal water supplies. The springs, issuing from Recent rocks on the upper slopes of the volcanoes, are generally temporary and fail in the dry season. Most of the permanent 

springs in the highland issue from Pleistocene or late Tertiary (?) 

rocks. Many of the larger ones issue from tongues of jointed and 

fractured lava of Pleistocene age interbedded with impermeable tuff 

and agglomerate. The smaller springs issue from thin beds of pumice 

or cinders in late Tertiary (?) tuff and agglomerate.

Underlying the plain of Candelaria and much of the area near Lago 

de Giiija are water-laid tuffaceous silts with interbedded strata of 

pumiceous and cindery sand and gravel. Pyroclastic materials of 

similar physical character are interbedded with these deposits along 

the margins of the lowland areas. The silts, clays, and fine sands 

that comprise most of the water-laid deposits are rather impermeable, 

but interbedded sand and gravel yield small to moderate supplies of 

water to dug wells and springs. The position of the regional water 

table beneath most of the lowland areas is controlled chiefly by the 

drainage level of the larger streams tributary to the Rio de Paz and 

Rio Lempa. Commonly springs rise along the stream channels in 

seepage lines from beds of pumiceous or cindery sand and gravel overlying impermeable strata of tuffaceous silt or sand. The yield of 

individual springs is small, but the aggregate discharge of a seepage 

line may be 50 to 100 gallons a minute or more. These spring lines 

represent outcrops of the water table. In the interstream areas wells 

for domestic and stock supplies must be dug approximately to the 

level of the spring lines to obtain adequate water supplies.

In the vicinity of kilometer 72 on the Pan American Highway, 

about 3y2 miles northwest of Santa Ana, the water table in December 

1943 was 78 feet below the land surface at two dug wells that are 85 

feet deep. These wells tap a stratum of water-bearing cindery sand 

interbedded with tuffaceous silt. The same stratum apparently crops 

out in a ravine near the crossing with the highway at kilometer 71. 

In this vicinity small springs issue along a line several hundred feet 

long and discharge in the aggregate about 100 gallons a minute. At 

kilometer 73 the water table is only 40 feet below the surface, but 

from this point westward to kilometer 77 on the highway the depth 

to the water table increases to 60 or 70 feet. Near kilometer 80, 4% 

miles southeast of Candelaria, water-bearing strata occur from about 

110 to 120 feet below the surface, and the water level in wells is at a 

depth of 105 to 115 feet.
214 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

In the section of the western plateau lying between Santa Ana and 

Coatepeque most of the wells and springs are supplied by water-bearing beds in Pleistocene pyroclastic rocks. About 650 feet north of the 

Pan American Highway, between kilometer 60 and 61 on the Arrara 

coffee plantation, is a dug well 52 feet deep. The well is reported to 

have penetrated several feet of water-bearing pumice underlying volcanic ash or tuff. The water level in the well was 48 feet below the 

surface in December 1943. The well yields a moderate supply of 

water throughout the year. At kilometer 61% a dug well on the farm 

of Jose Manuel Siguenza encountered a stratum of water-bearing 

cinders at a depth of 194 feet. The water level was 190 feet below 

the land surface in December 1943.

Approximately 1 mile northwest of Coatepeque, near kilometer 55 

on the Pan American Highway, is the spring of El Milagro. It 

rises in a semicircular spring-sapped alcove about 50 feet wide. The 

water-bearing bed is a 4-foot stratum of volcanic cinders that lies between massive beds of tuff. The flow is approximately 75 gallons a 

minute and is perennial.

Southwest of Coatepeque the regional water table in the upland areas 

is generally deep, and small springs fed by perched ground-water 

bodies are the chief sources of water. Typical are the springs on the 

Los Angeles plantation near Potosi. These springs issue from thin 

stringers of pumice in volcanic tuff. The dry-season flow is less than 

2 gallons a minute. At kilometer 48% on the highway a well 137 feet 

deep obtains a small domestic supply from a stratum of volcanic sand. 

The depth to water is reported to fluctuate between 123 and 129 feet 

below the land surface. At one time the owner attempted to deepen 

the well to obtain a greater yield, unsaturated permeable material was 

encountered and water from the sand stratum started to leak away, 

the well to obtain a greater yield; unsaturated permeable material was 

low the sand stratum. These conditions suggest that in this vicinity 

the water-bearing sand stratum is perched with respect to the regional 

water table.

Near the western edge of the Zapotitan basin, in the vicinity of 

Chilamatal, the low-lying springs that issue from the pyroclastic 

rocks are generally outcrops of the regional water table. In the valley 

of the Rio La Joya west and northwest of Chilamatal are several 

springs of considerable size. Nearly all of them issue from permeable 

beds of volcanic cinders or sand interbedded with volcanic tuff, agglomerate, and lava flows. The uppermost springs of the Rio La Joya 

rise along the stream channel about li/4 miles northwest of Chilamatal. 

A few hundred feet below the highest spring head the discharge of 

the stream is perhaps 5 cubic feet per second. Downstream the flow 

is augmented from place to place by smaller springs. Directly west 

of Oiilamatal at the base of a steep bluff is the spring of El Jute,
DEPARTAMENTO DE SONSONATE 215

which furnishes most of the domestic requirements of the townspeople. 

This spring issues from a thin bed of volcanic cinders overlying tuff 

in a small spring-sapped recess. The flow of approximately 50 gallons 

a minute finds its way to the Rio La Joya, a few hundred feet below 

the spring orifice.

In the Metapan region and the adjacent northern highland areas 

of Departamento de Santa Ana, sandstone, shale, conglomerate, marl, 

and limestone of Upper Jurassic and Lower Cretaceous age are reported. These rocks belong to the Metapan formation. They are in 

part overlain by weathered porphyries, andesites, and phonolites with 

intercalated pyroclastic rocks and detrital sediments, including sandstone and conglomerate of probable early (?) Tertiary age. The 

ground-water conditions of this region are not well known, but it 

is probable that the rocks generally have low permeability, owing to 

cementation and induration of sedimentary beds and alteration of 

volcanic materials. Locally the fragmental and scoriaceous facies of 

the lava flows may yield moderate to large supplies of water to wells 

and springs.

DEPARTAMENTO DE SONSONATE

GENERAL FEATURES

The Departamento de Sonsonate lies in the western part of El Salvador. It covers an area of approximately 740 square miles and has 

a population of 110,550. Within the department are parts of the 

coastal plain and the western plateau with adjacent sections of the 

Apaneca-Santa Ana highland and Zapotitan basin. (See pi. 3.)

The rocks underlying the western plateau are chiefly Pleistocene and 

late Tertiary (?) pyroclastic materials with interbedded lava flows. 

Similar rocks underlie the coastal plain, but they are venee.red in part 

by stream deposits of the Rio Grande and neighboring strea-ms. The 

Zapotitan basin is underlain chiefly by lacustrine and alluvial materials derived from pyroclastic rocks in the neighboring highlands.

GROUND-WATER CONDITIONS

The rocks underlying the western plateau and much of the coastal 

plain include large masses of volcanic tuff, agglomerate, pumice, and 

cinders interbedded with andesite lava flows. The beds of pumice and 

cinders and the fragmental and scoriaceous zones of the lava flows are 

generally permeable. Where they lie in the zone of saturation they 

supply many of the wells and springs in the department. For example, 

Chilata springs, which furnish the water supply of San Julian, rise 

from fragmental zones in andesite lava flow that lies above a mass of 

f dense volcanic tuff. The springs issue from three closely adjacent 

orifices, and the discharges are united at a central collecting box. The 

flow is delivered by gravity through a pipeline to the town. The
216 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

total discharge of the springs is about 100 gallons a minute. In San 

Julian and the surrounding valley area the water table is at relatively 

shallow depth,. and domestic dug wells tap water-bearing beds of 

pumice or cinders interbedded with volcanic tuff 15 to 25 feet below 

the surface in and near the town.

In the vicinity of Armenia, along the courses of the Rio Agua 

Caliente and the Rio Teguaya, numerous small perennial springs issue 

from beds of pumice overlying tuff. A typical example is Totonilco 

spring, l!/2 miles east of Armenia near the track of Salvador Railway. 

The spring issues from a thick bed of pumice in a .steep bluff overlooking the Rio Teguaya. It discharges about 25 gallons a minute. 

A well dug along the Nueva San Salvador-Armenia road about half a 

mile northeast of Armenia, at the Plan del Coco farm, encountered a 

stratum of water-bearing pumice interbedded with volcanic ash at a 

depth of 17 feet. The well is reported to furnish an adequate water 

supply for domestic use throughout the year. In the vicinity of Sonsonate near Nahulingo a number of large springs in a swampy tract 

rise from Pleistocene or late Tertiary (?) volcanic rocks. The discharge from these springs is several cubic- feet per second. Other 

large springs that issue from permeable zones in late Tertiary (?) 

volcanic rocks in the western plateau and coastal-plain areas contribute most of the low-water flow of the tributaries of the Rio Grande, 

the Rio Chiquihuatl, and the Rio Tazulate. Along the lower reaches 

of these streams near the coast the thickness of the alluvial deposits 

increases and the basal parts are in the zone of saturation. In limited 

areas they are tapped for domestic water supplies by dug wells a few 

tens of feet deep.

The ground-water conditions in the Apaneca-Santa Ana highland 

have not been studied in Sonsonate, but it is probable that they are 

quite similar to conditions in the highland in neighboring Santa Ana 

and Ahuachapan.

LOCAL SUPPLIES

ARMENIA

The city of Armenia (population 8,500) has an inadequate public 

water supply of doubtful sanitary quality. It is obtained from two 

spring developments and a small surface-water dam on the San Eugenio plantation 1 to 1% miles south-southwest of the city. The 

spring nearest the city is on a hillside in the narrow valley of the 

Rio Teguaya. It issues from fractures or small openings in tuffaceous 

agglomerate. About a quarter of a mile upstream a smaller spring, 

which also issues from volcanic agglomerate, discharges about 15 

gallons a minute.

Along the Rio Agua Caliente and the Rio Teguaya, which border 

Armenia on two sides, numerous small perennial springs issue from
DEPARTAMENTO DE TJSULATAN 217

a bed of pumice overlying impermeable tuff. These springs are fed 

by a water-bearing bed that underlies the city and the adjacent area. 

The position and location of the springs suggest that in the vicinity of 

the plaza the water table should be approximately 200 feet below the 

surface, and that one or more water-bearing beds would be encountered by a well drilled 250 feet deep. One or two wells of this depth, 

if properly developed, completed, and fitted with efficient pumping 

equipment, should furnish an adequate water supply for Armenia.

SAN JULIAN

The town of San Julian (population 1,500) has a water supply of 

about 144,000 gallons a day, or 96 gallons per capita. The supply is 

obtained by gravity pipeline from the springs of Chilata, ajbout 1*4 

miles south of the town, and is more than adequate for the present 

needs.

DEPARTAMENTO DE T7ST7LATAN

GENERAL FEATURES

The department of Usulatan lies in the east-central part of El Salvador. It has an area of approximately 1,270 square miles and a 

population of 150,000. The area includes most of the Tecapa-San 

Miguel highland, with bordering sections of the western plateau, and 

a part of the coastal plain with the lower valley of the Rio Lempa. 

(See pi. 3.)

Within the department the Tecapa-San Miguel highland is underlain chiefly by pyroclastic rocks and lava flows of Recent and Pleistocene age. The western plateau and the inland margin of the coastal 

plain are underlain chiefly by late Tertiary (?) volcanic rocks. Along 

the seaward margin of the coastal plain the late Tertiary (?) rocks 

are veneered by Pleistocene and Recent alluvial deposits.

GROUND-WATER 'CONDITIONS

The rocks that compose the Tecapa-San Miguel highland include 

a heterogeneous assortment of pyroclastic tuffs, agglomerates, pumice, 

and cinders, with interbedded tongues of andesitic and basaltic lava. 

The scoriaceous and fragmental zones in the lava flows and the pumice 

and cinder beds are highly permeable. Where they are present in the 

zone of saturation they yield moderate to large supplies of water to 

wells and springs. The volcanic tuffs and agglomerates are not generally permeable but locally they yield small supplies of water to wells 

and springs.

Near California, in the low area between Usulatan and Cerro del 

Tigre volcanoes, a local perched water-bearing zone occurs in a thin 

pumice bed in volcanic tuff. Numerous dug wells ending in this zone 

obtain small but perennial domestic supplies.
218 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

In a community well, "El Pozon," about half a mile north of California, this water-bearing zone is 52 feet below the surface and the water 

level is 48 feet.' The well furnishes a perennial domestic water supply for several families. A well dug in the plaza of California encountered the same water-bearing zone at a depth of 50 feet. In an 

attempt to obtain a more abundant supply this well was deepened to 

196 feet. At this depth the well was abandoned when permeable but 

unsaturated material in the upper part of an andesitic lava flow was 

encountered and the water from the higher perched zone began to 

leak away.

The city of Santiago de Maria obtains its water supply from a 

drilled well 272 feet deep which is located at the western outskirts. 

The principal water-bearing zone occurs in a scoriaceous and fragmental zone in a basaltic lava flow between 260 and 272 feet. The 

water from this zone rises in the well to 196 feet below the surface. 

The well yields 60 gallons a minute with no noticeable drawdown.

About 2% miles northeast of Berlin on the road to Mercedes Umaiia 

are the springs of Guallinac. They issue from tabular partings and 

scoriaceous zones in the base of a narrow tongue of andesitic lava overlying dense volcanic tuff. The total flow 'of the springs is estimated 

at 80 gallons a minute. They have been developed for the washing 

of coffee at two nearby coffee plantations.

The western plateau and the coastal plain are underlain chiefly 

by late Tertiary (?) pyroclastic rocks with interbedded lava flows. 

Similar rocks of Pleistocene age occur locally. The pyroclastic rocks 

are chiefly massive tuffs, and tuffaceous agglomerates with interbedded strata of cinders and pumice. Lava flows .exist locally but are 

not as extensive in the late Tertiary (?) as in the Pleistocene rocks. 

The pumiceous and cindery beds and the scoriaceous and f ragmental 

zones in the lava flows are permeable to water and where present in 

the zone of saturation yield small to moderate supplies to wells and 

springs.

In and near Jiquilisco an extensive water-bearing bed occurs in 

pumiceous zones and tabular partings in massive tuffaceous agglomerate. Many dug wells in the town obtain small domestic supplies 

from this bed at depths ranging from 25 to 35 feet below the surface. 

East of Jiquilisco, a quarter of a mile and half a mile, respectively, 

are the spring groups of El Chuchu and El Cacao, which rise in numerous minor orifices from the same water-bearing zone. The aggregate discharge of the springs of El Chuchu is perhaps 200 gallons a 

minute, and that of El Cacao is about 300 gallons a minute.

Just south of Usulatan are the springs of El Molino, which are 

among the largest in El Salvador. They rise from six adjacent orifices in a shallow spring basin. All the springs apparently issue from 

permeable material in a brecciated zone at the base of an extensive
DEPART AMENTO DE TJSULATAN 219

bed of andesitic lava overlying volcanic tuff. The total discharge 

of the springs is estimated to be about 50 second-feet. Directly west 

of Usulatan is a group of several springs which have an aggregate discharge of about 500 gallons a minute. They rise in adjacent springsapped alcoves from a pumice bed in massive volcanic tuff. This 

same water-bearing bed apparently supplies dug domestic wells 35 to 

45 feet deep in Usulatan and appears to lie above the beds which supply the springs of El Molino.

Just north of Mercedes Umafia, near kilometer 101 on the Pan 

American Highway, are the springs of the Bio Uinaria. They issue 

from a lenticular tongue of highly permeable andesitic lava 150 feet 

or more wide and 40 feet thick at the maximum. Around the spring 

zone the lava tongue is completely enclosed by dense massive tuff and 

tuffaceous agglomerate so that the lava tongue acts as a conduit or 

ground-water artery from which the water issues with considerable 

force. The discharge is estimated to be 10 cubic feet per second or 

approximately 4,500 gallons a minute. The springs are the chief 

source of water for the townspeople of Mercedes Umana and for 

travellers along the highway for a distance of several miles in either 

direction.

El Guiligiiiste springs, about a quarter of a mile northeast of Nueva 

Granada, are the principal source of water supply for that town. The 

springs issue from small cavities and. crevices in dense volcanic tuff 

in a line of small seeps about 150 feet long and have an aggregate discharge of about 15 gallons a minute. About 600 feet east of El Giiiligiiiste springs is the spring of El Chorro de Zapate, which rises from 

a ledge of andesitic or basaltic lava beneath a layer of volcanic tuff 

and discharges approximately 25 gallons a minute. Because neither 

of these springs is considered an adequate source of water supply, 

the Salvadorean Department of Public Works has undertaken the construction of a dug well in the town plaza. In October 1943 the well 

had reached a depth of 171 feet in tuff and agglomerate of late Tertiary (?) age and had encountered no important water-bearing materials. It is believed that if the construction of the well is continued 

to a depth of at least 325 feet one or more perennial water-bearing 

zones should be encountered. The well when properly developed, 

finished in the water-bearing zone, and fitted with an efficient pump 

should furnish an adequate water supply for Nueva Granada.

The townspeople of El Trinnfo obtained their principal water supplies from three small springs that rise from rocks of late Tertiary 

(?) age in the vicinity of the town. El Ujustal spring rises in the 

bottom of a deep canyon about half a mile north-northwest of the 

town. It flows about 5 gallons a minute from a thin, short lens of 

pumice and cinders that lies within a mass of volcanic tuff. About a 

mile north of town is the spring of El Riito, which also issues from a
220 GROUND-WATER RESOURCES OF EL SALVADOR, CENTRAL AMERICA

thin lens of cinders in dense tuff and tuffaceous agglomerate. The 

discharge is about 2 gallons a minute in the wet season. About 1% 

miles west of town is the spring of La Cueva. It issues from a thin 

bed of volcanic cinders overlying tuff and discharges about 4 gallons 

a minute.

To alleviate the shortage of water in El Triunfo, the Salvadorean 

Department of Public Works has undertaken the construction of a 

dug well in the town plaza. In August 1943 the well had reached a 

depth of 232 feet, about 50 feet below the top of a flow of dense 

andesitic lava. One or more water-bearing zones will probably be 

penetrated within a depth of 32-5 feet. When properly finished in the 

water-bearing zone, developed, and fitted with an efficient pump, the 

well should furnish an adequate water supply for El Triunfo.

LOCAL SUPPLIES 

ALEGRfA

The town of Alegria (population about 2,000) has a public water 

supply of approximately 6,000 gallons daily, or 3 gallons per capita. 

The supply is delivered by gravity pipeline from two collection tunnels on small springs about half a mile west of the town. These 

springs discharge about 4 gallons a minute from tabular partings in 

tuffaceous agglomerate.

JUCUAPA

The city of Jucuapa (population 5,500) has a public water supply 

of approximately 86,000 gallons a day, equivalent to about 16 gallons 

per capita. The supply reaches the city by gravity through two pipelines from the springs of Los Naranjos, Pico Blanco, Chahuite, and 

Agua Caliente.

Los Naranjos spring, about 1*4 miles northeast of the city, rises in 

a ravine near the top" of a hill. It issues from volcanic agglomerate 

and discharges approximately 30 gallons a minute. Chahuite spring, 

about li/4 miles east of the city, issues from a bed of volcanic cinders. 

The discharge of this spring, together with that of Pico Blanco, is 

about 17 gallons a minute. Agua Caliente spring discharges about 

13 gallons a minute, and the flow reaches the city by an independent 

gravity pipeline.

Near Jucuapa are two wells constructed for the supply of two coffee 

mills. One of these is 325 feet deep; the other, at lower elevation, is 

221 feet deep and yields 15 gallons a minute. A large part of Jucuapa 

is underlain by beds of highly permeable pumice and volcanic cinders. 

A well drilled in the vicinity of Jucuapa would encounter one or more 

productive water-bearing beds of these materials within a depth of 

400 feet. Such a well would considerably augment the existing water 

supply.
DEPARTAMENTO DE USULATAN 221 

tlStTLATi-N

The city of Usulatan (population 8,000) has a public water supply 

of approximately 100,000 gallons a day, or an average of abput 12 

gallons per capita. The supply is obtained from a pumping plant 

at one of the springs of Molino just south of the city. The water is 

raised to a storage tank in the upper part of the city and from there is 

distributed by gravity.

The present developed water supply is inadequate for the needs of 

the city. The additonal available supply at El Molino springs is 40 

to 50 cubic feet per second. By installation of larger and more efficient pumping equipment, by increasing and enlarging storage facilities in the city, and by improvements in the delivery and distribution 

pipelines, the developed water supply of the city would be increased 

threefold or fourfold.

INDEX

Page 

Acknowledgments _____________ 157

Agua Caliente, spring near Jucuapa____________ 220

spring, near San Vicente__ 212 

Aguila.________________ 164

Aguilares, plain of_____________ 168,

193-194, 206, pi. 3 

Ahuachapdn, city of, water supply____________.___________ 189

Departamento de______ 189-190

Algeria, municipal water supply. 220 

Alluvial fans__________ 174-175 

Alluvium, terraces_________ 177-178

Andesitic lavas____________ 181-184

Antiguo Cuscatlan, municipal

water supply____ 197

Apaneca, Volcdn de__ _ 163-164, pi. 3

Apaneca-Santa Ana highland. 163-165,

187-189, 212-213

Apantes, springs._____________ 200

Aponilla, spring_______________ 189

Area_.________---._______ 158

Armenia, municipal water supply____---_-_-.________ 216-217

Atiquizaya, municipal water supply for._.___-..__-.______ 189-190

Ayagualo, spring.___.__.__ 196, 198

Beach deposits________________ 173

Cabanas, Departamento de___ 190-191 

Cadena Costera.__________ 166, 182

California, ground-water conditions_________________ 217-218

Candelaria, plains of ________ 168-169,

187-188, 212-213, pi. 3 

Catorce de Julio, springs.______ 191

Central highlands, description

of-_-_-_____.__________ 163-168

Cerro del Tigre..-.-_._ 167, pi. 3 

Cerro San Juan, volcano. _ _ _ 163, pi. 3 

Chahuita, spring._____________ 220

Chalatenango, Departamento de. 191-

192

Page 

Chalatenango, plains of._______ 169,

191-192, pi. 3

Chichontepec, Volcan___ 166-167, pi. 3 

Chilamatal, springs near_ _ _ _ _ 214-2S5

Chilanga, spring._ __________ 203

Chilata, springs._____ 215-216, 217 

Chinameca, Volcdn ______._. 167, pi. 3

Civil divisions.______._--___ 158-159

Climate.----.-------------- 159-161

Coast Range. See Cadena Costera.

Coastal plain. _ _ 169-170, 200-201, 211 

Coatepeque, caldera sink of_____ 164

Cojutepeque, municipal water

supply____------_ 194

Cojutepeque, Volcd,n____ 166, 182, pi. 3

Cojutepeque highland________ 166,

190, 192-193, 209-210 

Colinas de Jucuaran. __ 170, 203-204 

Cretaceous rocks____________ 185-186

Cu«catld,n, Departamento de__ 192-195

Dacite.__________ 184 

Dolomitic limestone__ ______ 185-186

Eastern upland- 169, 200, 201, 203-204 

El Almendro, springs_________ 211

El Cacao, spring_____________ 218

El Carmen, municipal water

supply_-__-----_- 194

El Carrizo, spring. _________ 210

El Chorro, spring._____________ 191

El Chorro de Zapate, springs. _ _ _ 219 

El Chuchu, spring.____________ 218

El Coro, springs _.__... _ _ _ _ 206-207

ElCubo,spring________---_-_- 212

El Giiiliguiste, springs.... .. 219

El Jicaro, springs______________ 201

El Jute, spring. _________ 214-215 

El Milagro, spring.____________ 214

El Molino, springs. _. 183, 218-219, 221 

El Pinar, spring.______________ 212

El Pital, springs._... 203 

EIRiito, spring_____--.__-__- 219-220

223
224 INDEX

Page

El Triunfo, water supply for__ 219-220 

El Ujustal, spring____________ 219

El Zapote, springs.____________ 211

Encuentras, spring_____________ 210

Estuarine deposits-____________ 174

Fossils._____________ 178-180

Geographic setting_________ 158-159

Geologic history, summary of. 170-173 

(ground water, source of ______ 186-187

Ground-water conditions. See 

names of civil divisions. 

Guadalupe, municipal water supply_________ 211-212 

Guallinac, springs _____________ 218

Guazapa, Volcan___________ 169, pi. 3

Guija, Lago de____________ 178-213

Historical background _________ 158

Hot springs_____________ 163-164

Ilohuapa, springs______________ 207

Ilopango, Laguna de________ 166, pi. 3

Inchanmichen, springs-______ 199,200

Intermontane basins______-__ 168-169

Introduction. _ ______________ 157-162

Izalco, Volcan______________ 165, pi. 3

Jiquilisco, water supply for_____ 218 

Jocoro, municipal water supply. _ 203 

Jucuapa, municipal water supply 220 

Jurassic rocks_ _ _____________ 185-186

LaBomba, spring__________ 207-208

La Cangreja, spring.___________ 193

La Catarata, spring.___________ 183

La Chacra, springs_________ 206-207

La Chorreras, spring. _ _ _ _ 185, 201-202

La Cu'eva, spring.,.___________ 220

La Fuente, spring.____________ 209

Laguna de Rana, volcano.._ 164, pi. 3 

Laguna Verde, volcano._____ 163, pi. 3

Lake deposits, of Pleistocene

age____________ 179-181

La Lagunita, volcano.______ 163, pi. 3

La Leona, spring._____________ 210

La Libertad, Departamento

de___._________ 195-198

La Mina, spring.______________ 191

La Montana, springs_________ 197

Landslides_ _ ---____-________ 174

Page 

La Paz, Departamento de____ 198-200

La Quinta, spring_____________ 212

Las Anonas__ _ ____ __ 185, 201-202

Las Dantas, springs _________ 183, 207

La Uni6n, Departamento de__ 200-202 

Local water supplies. See under

names of cities. 

Location. __________________ 158, 159

Loma Larga, springs.__________ 198

Los Chorros springs, near Nueva

San Salvador. _ _ 179,

195-196

near Tonacatepeque_______ 209

Los Naranjos, spring.________ 220

Los Piedrones, spring._________ 189

Mastodons, remains of _______ 178, 180

Mejicanos, municipal water supply__--___---_- 207-208 

Mercedes Umana, water supply

for_-________---_ 219

Metapan formation. _____ 185-186, 215

Monserrat, springs____________ 207

Morazan, Departamento de__ 202-203

Naranjo, volcanic cone___._--_- 164 

Northern highlands.___________ 169

Nueva San Salvador, municipal

water supply. __ 197-198

Petaca, spring ________________ 210

Phonolite.___________-._ 184

Physiographic districts....-.- 162-170

Physiography, general features._ 162 

Pico Blanco, springs.__________ 220

Pleistocene deposits._______ 177-181

Population, ________________ 158-159

Potosi, springs near__________ 214

Prusia, wells near.____________ 206

Pumice-.-.. 178-179

Purpose of the investigation...- 157 

Pyroclastic deposits________ 178-179

Pyroxene andesites____________ 184

Quaternary lavas, of Pleistocene

age------..---- 178-179

of recent age__________ 176-177

Quezaltepeque, municipal water

supply.____-._-_- 197

Rainfall, table of_---__--- - 161 

Recent series, deposits of the____ 172,

173-177
INDEX 225

Page 

Rio Lempa___._____________ 162

Rhyolite__.____________ 184

San Andres, springs ___________ 198

San Cayetano, springs.--______ 211

San Francisco, municipal water

supply______-____ 203

San Julian, municipal water supPly___________-._ 217

San Martin, municipal water supply____________ 208-209

San Miguel, Departamento de_ 203-204 

Volcan de_____.__ 167-168, pi. 3

San Rafael Cedros, municipal

water supply. _____ 194

San Salvador, city of, water supply______---__.__ 206-207

Departamento de______ 204-209

Volcan de___.__ 165-166, pi. 3 

San Salvador highland.__ ___ 165-166,

193, 195-196, 199, 205-206

Santji Ana, Departamento de_ 212-215

Volcan de_ _________ 164-165, pi. 3

Santa Irene, springs.________ 199,200

Santa Rosa, municipal water

supply_________ 201-202

Santa Tecla. See Nueva San

Salvador.

Santiago de Marfa, water supply of____________ 218

San Vicente, city of, water supply___.__________ 212

Departamento de______ 209-212

San Vicente highland. 166-167, 199, 211 

Sensuntepeque, municipal water

supply.._________ 191

Sequence of rocks.____________ 170

Sonsonate, Departamento de__ 215-217 

Springs. See name of spring. 

Springs, temporary ____________ 177

Page

Stalactite and stalagmite deposits. 186 

Stratigraphic section.._______ 172-173

Talule, spring_________________ 190

Talus_________-___.__-_-_-- 174, 175

Tecapa, Volcan de________ 167, pi. 3

Tecapa-San Miguel highland. 167-168,

217 

Tertiary rocks__________ 181-185

Tonacatepeque, municipal water

supply._______ 209 

Tortuguero, spring ____________ 189

Totonilco, spring-_____________ 216

Trachyte________ _____________ 184

Tuff___________---___-___-- 178-186

Usulatan, Departamento de__ 217-221 

springs at city of __________ 183

water supply of city of_ ____ 221

Volcan_______________ W7, pi. 3

Verapaz, springs_____--_------ 211

Villa Delgado, municipal water

supply_____-_____ 208

Volcanoes ____________________ 163

See also names of individual 

volcanoes as listed 

on pi. 3.

Water-bearing properties of the

rocks___:______ 173-186

Water table, fluctuation._______ 187

See also under names of civil

divisions. 

Western plateau._________ 168-169,

199, 205-206, 209, 214, 215

Zacatecoluca, municipal water

supply___________ 200

Zapotitan basin____-_______ 168-169,

180, 181, 195-196, 206, 212-213