Geology 

Northern 

of Salars 

Chile 

• 

Ill 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 811 

Prepared in cooperation with the 

Instituto de Investigaciones 

Geoldgicas de Chile 

Geology 

Northern 

of Salars 

Chile 

By GEORGE E. STOERTZ and GEORGE E. ERICKSEN 

• 

Ill 

GEOLOGICAL SURVEY PROFESSIONAL PAPER 811 

Prepared in cooperation with the 

Instituto de Investigaciones 

Geoldgicas de Chile 

Description of the distribution, geology, and 

environmental setting of salt-encrusted playas 

and their closed drainage basins in Atacama, 

Antofagasta, and Tarapacd Provinces 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON 1974 
UNITED STATES DEPARTMENT OF THE INTERIOR 

ROGERS C. B. MORTON, Secretary 

GEOLOGICAL SURVEY 

V. E. McKelvey, Director 

Library of Congress catalog-card No. 73-600291 

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

Washington, D.C. 20402- Price $1.65. (paper cover) 

Stock Number 2401-02455 
Abstract ----------------------------------------

Introduction -------------------------------------

Present study ------------------------------- Previous investigations ----------------------

Acknowledgments ----------------------------

Environment of interior drainage basins ----------

Distribution and physiography ---------------

Coastal Range and Central Valley --------

Atacama Basin and vicinity --------------

Andean llighlands -----------------------

Climate ------------------------------------- Precipitation and temperature -----------

Evaporation -----------------------------

VVind -----------------------------------

Regional geology --------------------------------

Coastal Range ------------------------------

Central Valley ------------------------------

Atacama Basin and vicinity ------------------

Andean llighlands ---------------------------

Clay playa surfaces and salar crusts --------------

Clay playas --------------------------------- liard evaporite crusts ------------------------

Layered massive rock salt with a rugged 

surface ------------------------------- Slabby or nodular silty rock salt ----------

Rugged gypsum or anhydrite -------------

Massive, coarsely crystalline rock salt -----

Smooth rock salt ------------------------

Silty nitrate-bearing salar crust ----------

Soft surfaces or crusts ----------------------

Moist saline soil ------------------------

Moist gypseous crust --------------------

Dry friable crusts -----------------------

Features of S'alar crusts in Chile -----------------

Features due to flooding by surface water -----

Salt cusps and crenulate margins within 

salars -------------------------------- Salt channels ---------------------------

CONTENTS 

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Features of salar crusts in Chile-Continued 

Features due to flooding by surface waterCo;ntinued 

Salt pseudobarchans ---------------------

Salt blisters ----------------------------

Gypseous ramparts ----------------------

Features formed by ground water and springs __ 

Salt cascades and salt terraces ------------

Brine po~s ----------------------------- Salt cones and cups ----------------------

Features formed by solution of salt by rainwater 

and fog -------------------------------

Salt saucers ----------------------------

Salt nodules ----------------------------

Salt pinnacles --------------------------

Salt solution tubes ----------------------

Salt stalactites -------------------------- Features formed by faulting and fracturing ---

Giant salt polygons ---------------------

Salt sag basins and escarpments ----------

Salt pressure ridges ---------------------

Salt veins ------------------------------

Features formed by wind action --------------

Dust lobes ------------------------------

Salt-stabilized dunes ---------------------

Phreatophyte mounds --------------------

Former lakes in northern Chile -------------------

Andean llighlands ---------------------------

Shorelines ------------------------------- Deltas ---------------------------------- Drainage changes during high lake levels __ 

Lacustrine sediments --------------------

Atacama Basin and vicinity ------------------

Central Valley and Coastal range -------------

Environment of present and former lakes ----------

Existing lakes ------------------------------

Former lakes --------------------------------

Conclusions -------------------------------------

References cited ---------------------------------

ILLUSTRATIONS 

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FIGURE 1. Index map of northern Chile showing location of salars and lakes ---------------------------- 2 

2. Map showing regions of interior surface drainage in northern Chile and nearby areas in Argentina, 

Bolivia, and Peru ------------------------------------------------------------------------ 3 

3. Profile across Antofagasta Province, northern Chile ------------------------------------------- 7 

4. Graph showing estimated relation between elevation and mean annual precipitation in five regions of 

northern Chile -------------------------------------------------------------------------- 10 

5. Photograph showing fault scarps and a sag basin in massive rock salt at Salina Guanillos, western border of Salar Grande -------------------------------------------------------------- 13 

6. Map showing asymmetrical zoning of salars and drainage basins in northern Chile --------------- 16 

7. Photograph of boiling spring and pool at southeastern edge of Salar de Surire ------------------- 17 

8-12. Map showing salars and basins of interior drainage in8. Northern part of Tarapaca Province---------------------------------------------------- 20 

9. Southern part of Tarapaca Province and northeasternmost part of Antofagasta Province_ 21 

10. Western central part of Antofagasta Province ----------------------------------------- 22 

III 
IV CONTENTS 

Page 

FIGURES 11-12. Map showing salars and basins. of interior drainage in-Continued 

TABLE 

11. Eastern central part of Antofagasta Province ----------------------------------------- 23 

12. Northeastern part of Atacama Province ----------------------------------------------- 24 

13-15. Geologic map of13. Salar de Pintados, Salar de Bella Vista, and Salar Grande ------------------------------ 25 

14. Salar de Pendernales ----------------------------------------------------------------- 26 

15. Salar del Guasco and Salar de Coposa ------------------------------------------------ 27 

16·. Histograms and cumulative curves showing size-gradation for the six types of clastic sediments 

listed in table 2 ------------------------------------------------------------------------ 28 

17-30. Photograph showing17. Active mud-cracked dry-clay playa near the Lacalle railroad station ------------------- 29 

18. Wind-eroded dry-clay playa sediments in the Pampa del Tamarugal --------------------- 29 

19. Pit in a clay playa near the north end of Salar de Pintados showing layers of anhydrite -- 30 

20. Layering of massive rock salt near the northwestern edge of Salar de Pedernales ------- 30 

21. Brine pool in thinly layered high-purity rock salt in the northern part of Salar de Pedernales --------------------------------------------------------------------------- 31 

22. Rugged perennial rock-salt crust showing delicate clinkerlike texture, southeastern part 

of Salar de Atacarn~ ------------------------------------------------------------ 31 

23. Section of rock-salt crust underlain by silty sand in cut along Pan-American Highway, 

Salar de Obispo ---------------------------~------------------------~------------ 32 

24. Rugged gypsum crust with clinkerlike texture, eastern side of Salar de Atacama ~-------- 33 

25. Massive coarsely crystalline rock salt in an active salt quarry, northern part of Salar 

Grande ----------------------~---~---------------------------------------------- 34 

26. Smooth thin rock-salt crust in flood plain, northwestern part of Salar de Maricunga ----- 34 

27. Pressure ridges in layer of white salt, southern part of Salar del Carmen -------------- 35 

28. Silty nitr~te-bearing salar crust, Salar de Pampa Blanca and Salar del Carmen __ .:...______ 35 

29. Soft gypseous crust underlain by a 10-20-in. layer of high-purity ulexite, Salar de 

Ascotan ------------------------------------~----------------------------------- 36 

30. Soft moist gypseous crus,t, eastern side of Salar de Punta Negra ------------------------ 37 

31. Diagrams of distinctive patterns observed on aerial photographs of salars and . basins of former 

lakes in northern Chile ------------------------------------------------------------------ 38 

32-45. Photograph sho,wing32. Salt blisters on rock-salt flood plain, northern end of Salar de Maricunga ------------ 41 

33. Gypseous rampart bordering saline pond at western edge of Salar de San Martin ------ 41 

34. Salt caseades and constructional salt terraces at the eastern side of the valley of Rio Salado 42 

35. Small brine pool in a thin rock-salt crust, eastern side of Salar de Atacama ----------- 42 

36. Salt cones on rugged perennial rock- S'alt crust in the northwestern part of Salar de Pedernales --------------------------------------------------------------------------- 43 

37. Formation of salt cones at Salar de Pocitos, Argentina -------------------------------- 44 

38. Salt saucers at Salar de Pocitos, Argentina ------------------------------------------- 45 

39. Salt saucers at Salar de Obispo ------------------------------------------------------ 46 

40. Features formed by solution of salt by rainwater and fog ----------------------------- 48 

41. Pressure ridges in rock-salt crust, Salar de Bella Vista ------------------------------ 50 

42. Salt veins outlining newly formed salt polygons, northwestern part of Salar de Maricunga 51 

43. A salt-stabilized sand dune, Salar de Bella Vista ________________________ :_____________ 52 

44. Phreatophyte mound in area of thin discontinuous salar crust, northern part of Salar de 

Pintados ------------------------------------------------------------------------ 52 

45 .. Diatomite layer deposited in a former lake, northwestern side of Salar del Guasco _______ 55 

46. Diagram showing topographic and climatic factors favoring occurrence of perennial lakes in closed 

drainage basins of northern Chile --------------------------------------------------------- 59 47~ Map showing estimated climatic changes necessary to produce lakes in closed drainage basins in 

northe·rn Chile --------------------------------------------------------------------------- 60 

48. Diagram showing topographic and climatic factors that would have favored formation of perennial 

lakes in dosed basins in the Andean Highlands of northern Chile --------------------------- 62 

TABLES 

1. Physiographic and climatic features of interior drainage basins and salars in northern Chile -----

2. Gradation characteristics and physical properties of clastic sediments from northern Chile _______ _ 

3. Location and size of the principal former lakes in northern Chile -------------------------------

4. Comparison of probable former lakes in the Atacama Basin and in the Central Valley (Gran Lago 

Soledad) -------------------------------------------------------------------------------

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56 
GEOLOGY OF SALARS IN NORTHERN CHILE 

By GEORGE E. STOERTZ and GEORGE E. ERICKSEN 

ABSTRACT 

Northern Chile, which includes the extremely arid Atacama Desert and the semiarid Andean Highlands, has more 

than 100 basins with interior drainage; most contain salars 

(salt-encrusted playas). The area of interior drainage totals 

more than 38,000 square miles, within which salars and clay 

playas extend over a total area of about 2,800 square miles. 

In addition, hills and valleys in the Atacama Desert are 

extensively covered either with a thin hard saline crust, 

chiefly salt-cemented soil, or with a powdery soil that has 

a high content of saline material, chiefly anhydrite and 

gypsum. 

The region has an exceptional variety of types of hard 

saline crusts that are generally rare in other deserts, and 

many morphological and structural salt features, some of 

which may be unique. Soft saline crusts and clay playas, 

more characteristic of arid regions elsewhere, are also present. Hard salar crusts have formed by deposition of saline 

material in open water or by capillary migration and evaporation of near-surface ground water. Such crusts generally 

range from a few inches to several feet in thickness. Locally, crusts may attain thicknesses of several tens of feet, 

and one salar, Salar Grande, is a basin filled with highpurity rock salt to a local depth of at least 560 feet. 

Six general types of hard salar crusts are distinguished: 

(1) layered massive rock salt with a rugged surface, (2) 

slabby or nodular silty rock salt, (3) rugged gypsum or 

anhydrite, (4) massive coarsely crystalline rock salt, (5) 

smooth rock salt, and (6) silty nitrate-bearing saline crust. 

Soft surfaces or crusts include moist gypsum-bearing crusts, 

which commonly contain nodules and layers of ulexite in 

Andean salars, and moist to dry puffy soils and crusts that 

contain gypsum, thenardite and mirabilite as the principal 

saline constituents. An unusual chemical feature of the salars and the desert soils of northern Chile is the general 

paucity of carbonate minerals (for example, trona, calcite, 

and aragonite) which are widespread in other desert regions. 

Among the many morphological and s·tructural features 

that can be recognized in and near salars of northern Chile, 

the most unusual occur in hard rock-salt crusts, which in 

themselves are scarce in other arid regions. Included are 

features due to corrosion of rock-salt crusts by windblown 

water or free-flowing surface water, such as: ( 1) salt cusps 

and crenulate margins of salars, (2) salt channels, (3) salt 

pseudobarchans, and ( 4) salt tubes. Constructional features· 

in the salars include: ( 1) gypsum buttresses at borders of 

saline ponds, (2) salt veins, (3) salt stalactites, and (4) 

salt cones. In some salars, new fresh-water springs have 

formed steep-walled brine pools in thick rock-salt crusts. 

Prominent salt cascades and constructional salt terraces 

have been built up in one Andean valley by springs that 

are fed by brine from a nearby salar ( Salar de Pedernales). 

Sag basins and prominent scarps occur along faults that 

cut through the salt mass of Salar Grande. 

Of . the 67 closed basins in the Andean Highlands of 

northern Chile, at least 35 show shorelines or deltas of 

former perennial lakes. Today only five perennial lakes occur 

in this area. The former lakes probably formed at one or 

more times during the Pleistocene and perhaps continued 

to form into Holocene time. They indicate a climate that 

was either more rainy or cooler, or both, during the time 

of their forma·tion. However, the absence of glacial features 

throughout most of the northern Chilean Andes indicates 

that the climate during the Pleistocene glacial stages was 

not greatly different from today's climate. It is estimated 

that perennial lakes would form in nearly all the Andean 

basins if the mean annual rainfall of the region above 

10,000 feet in altitude were increased to 15 inches from its 

present 8 inches, and if the mean annual temperature were 

about 2° F. less than it is at present. 

INTRODUCTION 

Northern Chile is predominantly an area of interior drainage where surface and ground water 

flow into closed basins to salars,I saline marshes, 

saline lakes, or clay playas. The region discussed in 

this report is in the northern Chilean provinces of 

Tarapaca, Antofagasta, and Atacama (fig. 1). It includes the extremely arid Atacama Desert, a coastal 

area in which are found the well-known Chilean 

nitrate deposits, and the semiarid Andean Highlands 

to the east. The area of interior drainage covers more 

than 38,000 square miles in Chile and extends eastward and southward into Argentina, eastward into 

Bolivia, and northward into Peru (fig. 2). More than 

100 closed basins occur within the Chilean part of 

this region, and approximately 100 of these contain 

salars, of which only the largest are shown in figure 

1. These salars extend over a total area of about 

2,800 square miles. 

This report describes the distribution, geology, 

and environmental setting of Chilean salars. Special 

emphasis is placed on the morphology, physical character, and mineralogical composition of salar crusts 

and on the geology of the adjoining basin floors. 

1 Salars, the term used in South America and in this report, are saltencrusted pla}'las. Similar landforms in the United States have been 

termed salt flats, or, less frequently, salt pans. 

1 
2 

70° 

GEOLOGY OF SALARS, NORTHERN CHILE 

SALARS AND LAKES 

1-Laguna Blanco 

2-Salar de Surire 

3-Salar de Coipasa 

4-Salar de Obispo 

5-Salar de Uyuni 

6-Salar de Empexo 

7-Salar del Guasco 

8-Salar de Coposa 

9-Salar de Pintados 

1 0-Salar de Bella Vista 

11-Salar Grande 

1 2-Salar de Sur Viejo 

1 3-Salar de Lagunas 

14-Salar de Llamara 

15-Cerra Soledad (mountain) 

16-Salar de Ollagiie 

17-Salar de San Martin 

18-Salar de Chiguana 

19-Salar de Ascotan 

20-Salar del Carmen 

21-Salar de Navidod 

22-Salar Mar Muerto 

23-Pampa Elvira 

24-Salar de lmilac 

25-Salar de Punta Negra 

26-Liano de Ia Paciencio 

27-Salar de Atacama 

28-Salar de Tara 

29-Pampa de Taro 

30-Salar de Aguos Calientes 

31-Salar de Pujsa 

32-Salar de Quisquiro 

33-Salar de Aguas Calientes 

34-Lagua Miscanti 

25-Solar de Loco 

26-Salar de Tolar 

37-Laguna de Tuyajto 

38-Salars de Aguos Calientes 

and Purisunchi 

39-Salar de Puler 

40-Salar de lncaguasi 

41-Salar de Aguas Calientes 

42-Laguna de Ia Azufrera 

43-Salar de Pajonales 

44-Salar de Gorbea 

45-Salar de Ague Amarga 

46-Salar de Ia Isla 

47 -Solar de las Pari nos 

48-Salar de Aguilar 

49-Salar de lnfieles 

50-Solar Grande 

51 -Solar de Pedernales 

52-Solar de Piedra Parada 

53-Lagunas Bravos 

54-Laguna Wheelright 

55-Laguna Escondida 

46-Salar Wheelright 

57-Laguna Verde 

58-Solar de Maricunga 

49-Laguna del Negro Francisco 

60-Salar de Cauchari 

61-Salar de Arizaro 

62-Salar del Hombre Muerto 

63-Salar de Antofalla 

64-Salar de Pocitos 

65-Salar de Pampa Blanca 

50 

50 

I I 

0 

I I 

0 

50 KILOMETERS 

50 MILES 

FIGURE 1.-Index map of northern Chile showing location of salars and lakes. 
INTRODUCTION 3 

0 50 100 200 300 400 KILOMETERS 

50 100 200 300 400MILES 

EXPLANATION 

CHILE ARGENTINA, 

BOLIVIA, 

PERU 

Regions of interior drainage; streams drain 

into salars and saline lakes 

Subregions containing many salars. those in 

Chile are as follows : 

A. Coastal Range and Central Valley 

B. Atacama Basin and vicinity 

C. Andean Highlands 

FIGURE 2.-Regions o.f interior surface drainage in northern Chile and nearby areas in Argentina, Bolivia, and 

Peru. 

Because salars receive the drainage from large 

basins and lose this moisture chiefly by evaporation, 

they are responsive to many aspects of the environment, including geologic, hydrologic, topographic, 

and climatic factors. An ultimate objective is to 

interpret the features of the salars in terms of the 

environment. 

PRESENT STUDY 

The study of the salars of northern Chile has been 

carried out in cooperation with · the Instituto de 

Investigaciones Geol6gicas (the national geological 

survey) of Chile. The work was initiated by Ericksen in 1961 as part of a reconnaissance investigation 

of the saline deposits, mainly nitrate deposits, of 

northern Chile. This early fieldwork, carried · out 

during a period of about 6 months in late 1961 and 

in 1962, was sponsored partly by the U.S. Technical 

Aid program and partly by the United Nations 

Special Fund. The results of this work were presented in a report prepared for the United Nations 

(Ericksen, 1963). 

Stoertz (unpub. data, 1966, 1967) made a study 

based on detailed examination of aerial photographs 

of about 75 of the salars of northern Chile, together 

with a review of published and unpublished data 

available in Washington. As. part of this work, photogeologic maps were made of about 35 of the salars. 

This investigation was supported by the U.S. Air 

Force Cambridge Research Laboratories and the 

U.S. Geological Survey. 

A field reconnaissance study, also supported by the 

U.S. Air Force Cambridge Research Laboratories, of 

20 salars in northern Chile was undertaken during 

the period May to July 1967. Interpretations of 

crustal types, previously distinguished on aerial 

photographs, were field checked, and maps of the 

salars were corrected and amplified on the basis of 

new field data. Morphological and structural features 

of salars were also studied, and samples of saline 

crusts, associated clastic sediments and of saline 

waters from springs, lakes, and salars were collected 

for laboratory study. 

Fifteen samples of clastic sediment were mechanically analyzed, including samples of playa clay 

or lake clay, playa silt, playa sand, dune sand, and 

beach sand and gravel from shores of former lakes: 

Laboratory determinations included sieve analyses, 

hydrometer analyses, liquid limit, plastic limit, specific gravity, and salt content. In addition, approximately 75 samples were examined microscopically 

for microfauna (diatoms and ostracodes), for identi,. 

fication of principal saline minerals, and for study of 

clastic grains. 

High-altitude vertical aerial photographs of ex-
4 GEOLOGY OF SALARS, NORTHERN CHILE 

cellent quality are available for nearly all of northern Chile, at scales from 1 : 45,000 to 1 : 65,000. Maps 

of the salars (figs. 6 and 8-15), tabular data, and 

many other interpretations are based on aerial 

photographs taken during the periods March 25 to 

April 30, 1955, and March 15 to May 15, 1961. This 

is likely to be a period of maximum flooding at most 

of the salars in the Andes, for it follows the summer 

rainy season of December through March. Therefore, these photographs were particularly useful for 

study of flood patterns in the salar crusts. It is estimated that flooding shown in photographs taken in 

1961 is typical of the average year because rainfall 

was average. From available records at Ollagtie, precipitation during the year prior to May 1961 was 

approximately 69 mm, close to the 7-year mean of 

78.5 mm. San Pedro de Atacama also appears to 

have had a typical rainy season during the summer 

before the photographs were made. The average 

annual rainfall here for 1959-1961 was 20.4 mm 

(Fuenzalida, 1966, table 1). 

The most up-to-date maps of northern Chile are 

topographic maps, at the scale 1: 100,000, published 

by the Instituto Geografico Militar of Chile, which 

cover the Coastal Range and Central Valley, and 

Operational Navigational Charts (ONC), at the 

scale 1:1,000,000, published by the U.S. Air Force, 

which cover the whole area. 

PREVIOUS INVESTIGATIONS 

Geological investigations of salars in northern 

Chile have been scanty; consequently, published reports are few and deal with only a few of the salars. 

A larger number of reports give more general information on geology, geomorphology, and hydrology of 

northern Chile. 

The principal reports on salars follow: Both Gale 

(1918) and Brtiggen (1918) described the potash deposits of Salar de Pintados. Bowman (1924) discussed the geography and climate of the Central 

Valley and Andes, described Salar de Atacama, Salar 

de Punta Negra, and others, and provided useful 

discussions of climate, former lakes, flooding, geomorphology, and surface conditions. Vila (1953) 

gave the most comprehensive description of the 

borate deposits in salars of northern Chile. He also 

briefly described deposits of sodium sulfate, potash, 

and rock salt of several salars. Stuven (1888) and 

Chamberlin (1912) also described a few of the borate deposits. Ericksen (1963) described the geology 

and mineral resources of several of the salars. 

The most up-to-date information about the geology 

of northern Chile is in Brtiggen (1950) and Ruiz 

(1965). In addition to the discussion of regional 

geology, Brtiggen (1950) gave considerable information about geomorphology, hydrology, and former 

lakes of the area. Darapsky (1900) described the 

geology and geography of the department of Taltal, 

the southernmost part of Antofagasta Province. The 

most comprehensive report on ground water in 

northern Chile is by Castillo (1960) ; it deals with 

the Pampa del Tamarugal in the Province of Tarapaca. Taylor (1947a, b, 1948, 1949) described 

ground-water resources of several areas in . northern 

Chile. Fuenzalida (1965, 1966) summarized information about the climate. 

Harrington (1961) studied the geology of parts 

of the Atacama Basin and part of the basin of Salar 

de Pedernales. Segerstrom (1962, 1963, 1964) .described the Quaternary geology and geomorphology 

of northern Chile. Dingman and Galli (1965) and 

Dingman (1967) reported on the geology and 

ground water in the regions of Pica and San Pedro 

de Atacama, respectively, including the northern 

parts of the Llano de la Paciencia and the Salar de 

Atacama. Salas and others (1966) described the 

geology and mineral resources of the Arica region, 

including Salar de Surire. Tricart studied the geomorphology of Salar del Guasco (unpub. data, 1967). 

ACKNOWLEDGMENTS 

Members of the Instituto de Investigaciones Geo16gicas (IIG) aided the work in many ways. Ing. 

Carlos Ruiz F., former director of the IIG, gave 

direct support and valuable advice during all phases 

of the work. Thanks for aid and information is given 

to the following geologists of the Instituto who accompanied us at various times during the field investigations: Nelson Bravo, Guillermo Chong, Hugo 

Conn, Francisco Ortiz, Gabriel Perez, Raul Salas, 

Jaime Sayes, and Arturo Thomas. Fernando Munizaga and Mauricio Tabac, respectively, made semiquantitative spectrographic analyses and X-ray 

diffractometer determinations of saline material 

from the salars. Hernan Cusicanqui made chemical 

analyses of saline waters and brines from salars and 

saline lakes. 

We wish to express our gratitude to the following mining companies in northern Chile who offered 

hospitality and aid during fieldwork: Anglo-Lautaro 

Nitrate Corp.; Borax Consolidated, Ltd., owner of 

borate deposits at Salar de Ascotan and Salar de San 

Martin; and Cia. Azufrera Ollagiie, owner of sulfur 

deposits at Volcan Ollagiie. 
ENVIRONMENT OF INTERIOR DRAINAGE BASINS 5 

The late Frank H. Humberstone supplied unpub- table 1 to show broad relationships and regional 

lished reports and information about explorations variations. Physiographic data were taken largely 

for potash in several of the salars. This information from the U.S. Air Force Operational Navigational 

was essential to the understanding of the chemistry Charts, scale 1: 1,000,000, supplemented by data 

of salars in the Coastal Range and Central Valley of from aerial photographs. Climatic data for northern 

northern Chile. Chile are scanty; data given in table 1 are estimated 

Thanks are given to Major James T. Neal, U.S. or extrapolated from information given by FuenzaAir Force Academy, and to Daniel B. Krinsley and lida (1965, 1966). Several parameters selected for 

Lawrence D. Bonham, U.S. Geological Survey, for showing regional variations in this table are based 

their support and advice during the investigation of on unpublished data of Jerry Harbour (1963), U.S. 

Chilean salars and in the preparation of this report. Geological Survey. 

ENVIRONMENT OF INTERIOR DRAINAGE DISTRIBUTION AND PHYSIOGRAPHY 

BASINS 

Within the region of interior drainage, the salars 

Information about physiographic and climatic fea- tend to be concentrated in three distinct subregions 

tures for each drainage basin and salar is given in (fig. 2) : ( 1) about one-sixth of the salars are in the 

TABLE 1.-Physiographic and climatic features of interior drainage basins and salars in northern Chile 

.. 

~ -; 

~ 

- ! .s .. -; '§ ~ ::I 0 

~ :e ~ i oj = = ~ 

.c ~ = ~ 'g ... "tt 'g 'S = II Ill ~ =E! 'il 

l ~ ~ ~ Q 

= =i ·;.._. .!3 = .e~ '"' ,g~ Gl.-. Ql.-. 

... 'g Q I1J E!~ E!~ .!3 

t .. ~ 10~ = ...,; ,g::_ 0 "i:l ~§; ~ II II 'i~ "tt' .. 'C._. 1 -; 

~ t t-- = .... Ql ... $._. $QI ·i II ... Ill 'GiC'l .c~ Ql. 

II -;CQ >' ~~= Ill= ....... 'GI =-- !:II .!3 ~::X:: s.s ~'"' '"' .!3 II =' >' ~-- .§.s '"' ... ao t = ~~- 11-. ... l:l:l ~s ~~ .c I1J :i:: II I1J ::s-- +'+> II • -;::::;- II ~ II Ql~ Ql~ co ~ ... ~t 11.111 ::I !:QeD !%IS ~ Ql 

~+ ~I rzl~ rzl'S, fzl~oo 00 oos ~ IZl J! Q -..; .-..ra --·2 ~ --~ --co --co ~ ~ §~ ~~ :!!:. ~,! 8-! ._.f ~:::~+> ._.'"' ... 

-"tt II ~t --~ 

t<~oo 

--~ ~j ._.t ~~~ ~ 

2 224 40 6 14,000 16,100 15,000 2,100 8.4 4.7 7 34 19 c 4 182 4.2 43 13,500 16,000 14,750 2,500 7.6 6.2 7 35 20 c 7 691 96 7 2,300 3,300 2,800 1,000 14.8 1.3 0 62 60 A 

8 55 45 A 9 6,280 280 22 3,000 10,300 8,500 7,300 44.7 3.1 

10 

11 624 16 39 12,500 14,600 13,500 2,100 14.1 2.8 5 40 26 c 12 434 94 13 12,205 14,800 12,500 2,600 11.8 4.2 5 40 26 c 14A 176 1.1 160 13,000 14,900 14,250 1,400 7.5 3.5 5 37 23 c 

15 211 44 5 12,500 14,600 13,500 2,100 8.2 4.8 5 40 26 c 

16 640 96 7 12,220 15,500 14,000 3,000 14.3 4.0 5 38 24 c 

17A 1,442 0.4 3,600 2,300 4.800 3,500 2,500 21.4 2.2 0.4 62 60 A 

17B 183 0.2 915 3,600 5,200 4,500 1,600 7.6 4.0 0.4 61 55 A 

17C 40 0.4 100 3,500 4,700 4,000 1,200 3.6 6.3 0.4 61 55 A 

17D 135 0.2 675 3,300 4,700 4,000 1,400 6.6 4.0 0.4 61 55 A 

19A 55'0 1.3 423 2,300 5,300 3,500 3,000 13.2 4.3 0.4 62 55 A 

21 165 0.9 183 8,500 9,700 9,000 1,21()0 7.2 3.2 0.8 54 44 B 

22 479 5.8 83 8,000 9,700 8,750 1,700 12.4 2.6 0.8 55 45 B 

22A 83 0.4 208 6,500 8,400 7,500 1,900 5.1 7.1 0.6 58 49 B 

23 135 2.0 67 7,500 10,500 9,000 3,000 6.6 8.6 1 54 44 B 

24 731 118 6 7,5'00 9,400 8,500 1,900 15.3 2.4 1 55 45 B 

25 4,529 1,225 4 7,500 13,900 10,750 6,400 38.0 3.2 2 49 36 B 

25A 45 0.8 56 10,500 11,400 11,000 900 3.8 4.5 2 48 36 B 

26 436 15 29 6,500 9,500 8,000 3,000 11.8 4.8 0.7 57 47 B 

26A 91 0.1 910 7,500 9,000 8,250 1,000 5.4 5.3 0.6 56 46 B 

27 324 9.9 35 7,500 10,000 8,750 2,500 10.9 4.3 0.8 55 45 B 

28 75 12 6 12,500 14.500 13,500 2,000 49 7.7 10 40 22 c 

29 156 21 7 12,500 14,000 13,500 2,000 7.0 5.4 10 40 22 c 

30 175 2.9 76 13,500 16,000 14,75'0 2,500 7.5 6.4 10 35 18 c 

31 400 56 7 13,5'00 16,000 14,750 2,500 11.3 4.2 10 35 18 c 

31A 91 0.8 114 13,500 15,800 14,750 2,300 5.4 8.1 10 35 18 c 

31B 15 0.2 75 14,500 15,700 15,000 1,200 2.2 10.3 10 34 17 c 

31C 55 0.2 275 14,500 15,500 15,000 1,000 4.2 4.5 11 34 16 c 

31D 61 1.5 41 14,500 15,700 15,000 1,2t00 4.4 5.2 11 34 16 c 

31E 124 6 21 13,500 16,600 15,000 3,100 6.3 9.3 11 34 16 c 

31F 29 0.1 290 13,500 15,()00 14,250 1,500 3.0 2.7 10 37 19 c 

32 252 7.6 33 14,500 16,000 15,500 2,100 89 4.5 11 32 15 c 

33 1•04 6.6 16 12,500 15,200 13,700 2,700 5.8 8.8 10 39 21 c 

See footnotes at end of table. 
6 GEOLOGY OF SALARS, NORTHERN CHILE 

TABLE !.-Physiographic and climatic features of interior drainage basins and salars in northern Chile-Continued 

.. 

~ .. ~ ~ 

.- ! .a .. .. '§ j ~ :a i ::s ~ & ~ ,; s= s= ,.Q ~ s= s= ... 'lo4 ii :;::: IS II ~ II ~ 0 s::S '; i s= :; ........ 

Ill 

s= s= ~ .e 81.- Ill ., s= .e~ ... .!:: cu.- ... ~ 0 Ill s~ Sr>:. .e ~~ 81 "'a~ II ~ ~t: s= .!::.. 0 i:: 'iii aS t- 'i::._ ~ .... , ... .,_ ., ... Cll s t S::.-< Cll ... $ ..... $cu $ 0 II ... Ill GlC'I ,.Qt: ,!ct.) :>' i .... aS ........ :;l aSS:: lis:; .erk 'il =' =- 11-..... :oltl:: s.sa ~~ ... .e ... = II .::I:Q ~- .§.a .§.sa '"' Ill 

~=- II 'i t = aS- aS.- ::s- :ei ~~ ,.Q ~~- 'iii:.: aS Clllil;l Clllil;l ~~:::~ 

~t Ill aS ::s ~t~s rna It! ~ Cll 

~+ ~I C' 

10:15 10:1'S, 10:1~ rn ~ J"o;111l -Ill ~.s .e -1 ,::1, .-,::1, :!e -C' ..... C' ~~ 

~ ~ §~ ~~ ...... ., ~t -a ~..'! ~..'! _.f ... 

._. II ... --,::~, ..... 

~:< ... 

,::~, ~.s ::l!\1~ _.CII ~ 

33A 49 0.2 245 14,500 16,400 15,500 1,900 4.0 9.0 10 32 16 c 34 118 6.7 18 13,500 15,800 14,750 2,300 6.1 7.1 11 35 17 c 35 264 97 7 13,500 15,000 14,250 1,500 9.2 3.1 11 37 18 c 

36 711 19 37 12,500 16,000 14,250 3,500 15.0 4.4 11 37 18 c 37 105 9.0 35 13,500 14,800 14,250 1,300 5.8 4.2 11 37 18 c 38 1,528 2.8 546 4,000 7,700 6,750 3,700 22.1 1.7 0.6 58 55 A 38A 81 0.2 405 7,500 8,200 7,750 700 5.1 2.6 0.4 57 48 A 38B 110 0.2 550 6,500 7,700 7,000 1,200 5.9 3.9 0.5 58 49 A 

38C 107 0.4 268 6,500 7,000 7,000 1,100 5.9 3.5 0.5 58 49 A 38D 54 0.2 270 7,500 8,000 7,750 500 4.1 2.3 0.5 57 48 A 38E 62 0.2 310 6,5'00 7,700 7,000 1,200 4.4 5.2 0.5 58 39 A 38F 45 1.2 38 3,500 4,000 3,750 700 3.8 3.5 0.4 61 55 A 38G 271 1.7 159 3,500 4,500 4,000 1,000 9.3 2.0 0.4 61 55 A 

39 1,668 99 17 9,534 13.100 11,250 3,600 23.0 3.0 2 47 35 B 39A 115 0.4 288 9,500 11,200 10,250 1,700 6.1 5.3 1 51 40 B 39B 122 1.0 122 10,500 11,300' 11,000' 800 6.2 2.4 1 48 37 B 39C 54 0.5 108 10,500 11,000 10,750 500 4.1 2.3 1 49 37 B 40 37 9 12 9,500 10,800 10,250 1,300 3.4 7.2 1 51 40 B 

41 310 9.6 86 9,500 12,500 11,000 3,000 9.9 5.7 2 48 36 B 41A 144 0.2 720 11,000 14,300 12,750 3,300 6.8 9.2 7 42 27 c 41B 36 0.2 180 12,000 12,800 12,500 800 3.4 4.4 7 43 28 c 41C 75 0.1 750 10,500 13,000 11,750 2,500 4.9 96 3 46 34 c 42 104 1.4 74 9,500 10,800 10,250 1,300 5.8 4.2 1 51 40 B 

43 97 1.0 97 12,000 14,560 13,250 2,500 5.6 8.4 9 40 23 c 44 283 19 22 11,500 15,900 13,750 4,400 9.5 8.8 10 39 20 c 44A 181 0.4 452 12,500 14,500 13,500 2,000 7.6 5.0 10 40 22 c 45 412 85 5 11,400 15,400 13,500 4,000 11.5 6.5 10 40 22 c 47 97 1.8 54 12,500 14,200 13,500 1,700 5.6 5.7 4 40 28 c 

49 244 91 8 10,500 14,&00 12,500 4,100 8.8 8.8 3 43 31 c 49A 60 2.6 23 11,500 13,500 12,500 2,000 4.4 8.6 3 43 31 c 50 A 80 1.1 73 12,500 13,800 13,250 1,300 5.0 4.9 4 40 28 c 51 152 9.4 16 11,500 13,800 12,750 2,300 7.0 6.2 3 42 30 c 51A 102 0.6 170 11,500 13,800 12,750 2,300 5.7 7.6 3 42 30 c 

52 690 40 17 11,500 13,800 12,750 2,300 14.7 3.0 3 42 30 c 52 A 36 0.2 180 12,500 14,800 13,750 2,300 3.4 12.8 7 39 24 c 53 A 17 0.6 28 13,500 15,200 14,250 1,700 2.3 14.0 7 37 22 c 54 283 19 22 13,500 15,500 14,500 2,000 9.5 4.0 7 36 21 c 55 139 12 11 12,500 15,200 13,750 2,700 6.7 7.6 7 39 24 c 

56 210 8.4 25 12,500 15,100 13,750 2,600 8.2 6.0 6 39 25 c 

56 A 57 0.7 81 12,500 15,200 13,750 2,700 4.3 11.9 6 39 25 c 57 333 75 4 13,500 15,100 14,250 1,600 10.1 3.0 8 37 21 c 

58 94 9.9 28 14,000 15,900 15,000 1,900 5.5 6.6 8 34 18 c 

58A 23 0.1 230 15,000 16,000 15,500 1,000 2.7 7.0 8 32 17 c 

59 168 10 17 13,500 15,300 14,500 1,800 7.3 4.7 8 36 20 c 

610 1,464 99 16 11,500 15,100 13,250 3,600 21.6 3.2 4 40 27 c 

60A 49 1.0 49 12,500 14,400 13,500 1,900 3.9 9.2 4 40 27 c 

61 866 56 15 11,500 15,400 13,500 3,900 16.6 4.5 11 40 21 c 

63A 31 0.3 103 13,500 15,300 14,500 1,800 3.1 11.0 8 36 20 c 

65 180 9.5 19 14,500 16,800 15,750 2,300 7.6 5.7 8 31 17 c 

65A 25 0.4 62 15,500 17,800 16,750 2,300 2.8 15.5 8 27 13 c 67 125 2.4 52 14,500 17.800 16,250 3,300 6.3 9.9 9 29 14 c 

67A 35 0.4 88 15,500 17,700 16,500 2,200 3.3 12.6 8 28 14 c 

68 154 4 38 14,500 16,000 15,250 1,500 7.0 4.1 8 33 18 c 

69A 33 1.7 19 14,500 16,000 15,250 1,500 3.2 8.9 8 33 18 c 

70 42 0.4 1<05 14,000 15,700 14,750 1,700 37 8.7 8 35 19 c 

70A 34 0.2 170 14,500 16,000 15,250 1,500 3.3 8.6 8 33 18 c 

70B 37 0.4 92 14,500 16,000 15,250 1,500 3.4 8.3 8 33 18 c 

71 72 1.5 48 15,500 16.700 16,000 1,200 4.8 4.7 9 30 16 c 

71A 134 0.3 447 14,500 17,000 15,750 2,500 6.5 7.3 9 31 16 c 

71B 58 0.2 290 16,000 17,300 16,750 1,300 4.3 5.7 9 27 14 c 

72 684 7.0 98 14,500 17,400 16,000 2,900 14.8 3.7 13 30 12 c 

74 360 8.0 45 13,500 15,500 14,500 2,000 10.7 3.5 15 36 14 c 76 103 0.5 206 15,500 18,000 16,750 2,500 5.7 8.3 13 27 11 c 

1 Italicized figures of salar areas were determined from large-scale aeria I photographs and have fair to good accuracy; areas of other salars were 

determined from maps and are generally less accurate. 2 Parameters described by Jerry Harbour (unpub. data, 1963). 3 Subregions are as given in figure 2. 
ENVIRONMENT OF INTERIOR DRAINAGE BASINS 7 

Coastal Range and Central Valley at elevations of 

1,700 to 7,500 feet; (2) about one-sixth are in a 

belt along the Andean front, including the Atacama 

Basin, at elevations of 6,500 to 10,500 feet; and (3) 

two-thirds are in the Andean Highlands at elevations 

of 10,500 to 16,000 feet. A southwest-northeast profile across Antofagasta Province between lat 23° and 

24°8. (fig. 3) illustrates the general setting of salars 

in relation to the major geographic subregions. 

COASTAL RANGE AND CENTRAL VALLEY 

The Coastal Range is characterized by subdued to 

moderately dissected terrain, generally consisting of 

rounded hills and rolling uplands at elevations of 

3,000-6,000 feet. Small mountains locally rise above 

the general level of the uplands, but relief is generally low. Much of the region has the character of an 

undulating plateau, which is fairly level when seen 

from a distance but which is dissected by shallow 

broad valleys and basins having a relief of generally 

not more than a few hundred feet. The western side 

of the Coastal Range is bounded by an abrupt escarpment, commonly 2,000-3,000 feet high, that 

shows evidence of recent faulting. The eastern side 

of the Coastal Range slopes gently eastward toward 

the Central Valley, where it either merges with the 

valley fill or terminates at a low escarpment. The 

eastern margin has the appearance of being partly 

covered or "drowned" by the sediments of salars 

and clay playas. · 

The Central Valley is a broad longitudinal depression between the Coastal Range and the Andean 

Highlands. Itstotal length, from the Peruvian border near Arica southward to lat 27°8., is about 600 

miles, and its maximum width is about 50 miles. It is 

a continuous broad valley in the northern part of 

Antofagasta Province and southern Tarapaca province, where it is known as the Pampa del Tamarugal 

(fig. 1). Here, it consists of a broad gently sloping 

alluvial plain at elevations mainly between 3,000 and 

7,000 feet. In Tarapaca, north of the Rio Loa (fig. 

2), the valley contains large salars in its lowest part 

along the western edge adjacent to the Coastal 

Range. From here the surface rises eastward toward 

the Andean Highlands at slopes ranging from less 

than 1 percent at the base to as much as 8 percent at 

Coas~l Range and Central Valley Atacama Basin and vicinity Andean Highlands 

!'! 

~ -t ~ !'! !- -~ 

~ ~~ (5 ~ ~ !- D 

~ ~! ~ !- !-

~ ~~ ~ ~ J5 J5 J5 Meters 

2,000 HH--4----+---4----~ 

1,500 

1,000 

500 

Ji 

>-

... 

a E 

D 0 

>- ! c D E ~ "'ii. <:3 

-~ ~ 0 ~ ~ 5 ;;> ~ ~ 0 

-o v ... <:3 ~ 0 E ~ !-

~ j ~ 

~ v J5 

VERTICAL EXAGGERATION APPROXIMATELY X 20.8 

VERTICAL EXAGGERATION APPROXIMATELY X 5.2 

0 10 2'J 30 40 50 KILOMETERS 

0 10 20 30 40 50 MILES 

-, 

I 

] I 

,- !'! 

~ 1 ~ ~ E ~ -" [ ~~ D ~ 

D g ... i ~ 

~~ i D. ~ u e ~ ·;: ~.§' E' ~ ... <:3 g 1 1 ~ 

0 ~ t~ j I 

> ~! :c D. I J5 v ... I 

1 Feet 

18,000 

16,000 

.·:· 

14,000 

12,000 

1(),000 

8,000 

6,000 

4,000 

2,000 

FIGURE 3.-Southwest-northeast profile across Antofagasta Province, northern Chile, between lat 23° and 24 o S., showing positions of three subregions of interior drainage. 
8 GEOLOGY OF SALARS, NORTHERN CHILE 

higher elevations. In addition to its distinct westward slope, the lowest part of the Pampa del Tamarugal slopes gently southward from an elevation of 

about 3,600 feet at a point east of Pisagua (lat 

19°40'S.) to about 2,700 feet in the northernmost 

part of Antofagasta Province (fig. 1). It again 

slopes gently upwards to the south and ends at about 

the latitude of Sierra Gorda. The Central Valley is 

interrupted by a broad transverse valley extending 

from Sierra Gorda, passing Baquedano, and draining into Salar del Carmen (fig. 1). Farther south it 

is represented by a large elongate basin of interior 

drainage that centers near Aguas Blancas and gives 

way southward to upland piedmont plains and broad 

alluvial valleys. 

In the subregion of the Coastal Range and Central 

Valley (fig. 2) , many salars and clay playaS' ··are 

found from the latitude of Pisagua in the north to 

near Antofagasta in the south, a distance of about 

300 miles. This region is interrupted by the exterior 

drainage basin of the Rio Loa. Drainage basins·in 

this subregion are large in comparison with those of 

the Andean Highlands of northern Chile. Sixteen 

basins having interior drainage are present; each of 

these has an average area of 960 square miles, and 

together they have a total area of about 15,360 

square miles. This is an area larger than the combined areas of 67 basins in the Andean Highlands. 

Basins of this subregion (table 1) have relatively 

low salar elevations (median 3,500 ft), low basin 

divides (median 6,000 ft), low basin relief (median 

1,200 ft) , and low basin slopes (median 3.3 percent) . 

ATACAMA BASIN AND VICINITY 

The eastern part of Antofagasta Province is 

marked by mountain ranges in front of the main 

Andes, the Cordillera Central in the north and the 

Cordillera Domeyko in the south (fig. 1). The Cordillera Central is separated from the main Andes by 

the broad valley of the Rio Loa, whereas the Cordillera Domeyko is separated by an elongate closed 

depression which contains the Salar de Atacama in 

the northern part and the Salar de Punta Negra in 

the southern part. 

Salars in the subregion of the Atacama Basin and 

vicinity, east and southeast of Antofagasta, are 

found over an area 20-50 miles wide and about 150 

miles long (fig. 2). Seventeen basins of interior 

drainage occur in this area, the Atacama Basin being by far the largest. They extend over a total area 

of about 9,500 square miles. These basins have the 

following characteristics ( U;tble 1) : median elevation of salars is 8,500 feet; median elevation of basin 

divides is 10,800 feet; median elevation of basins is 

9,600 feet; median relief of basins is 1, 700 feet; and 

median slope of basins is 4.3 percent. 

ANDEAN HIGHLANDS 

The Andean Highlands of northern Chile constitute an undulating plateaulike region having several 

north-trending ridges and hundreds of volcanic 

peaks with intervening broad, relatively shallow valleys and basins, many of which have internal drainage. Topography is relatively gentle, although relief 

is locally great. Base altitude of the region is 13,000-

14,000 feet, and the highest volcanic peaks range 

from about 18,000 to 22,000 feet. 

Salars oecur "in the Andean Highlands of Chile 

from Salar de Maricunga (northeast of Copiapo) in 

the south to Salar de Surire in the north (fig. 1), a 

distance of nearly 600 miles. There are 67 closed 

basins in this region. Salars also occur in the Andes 

of northern Argentina, western Bolivia, and southern Peru, within the areas of internal drainage 

shown in figure 2. Salar de Uyuni in western Bolivia 

(fig. 1) is by far the largest salar in South America. 

In Chile, the Andean Highlands are separated into 

two areas of interior drainage by the through-flowing drainage system of the Rio Loa. The basins in 

these two areas tend to be small, in comparison with 

basins in the other two subregions in Chile, averaging only 205 square miles per basin. The total area 

of interior drainage in the Chilean Andes is about 

14,060 square miles. Among the general characteristics that distinguish the Andean basins from those 

to the west (table 1) are high salar elevations 

(median 13,500 ft), high basin divides (median 

15,400 ft), high bH.sin elevations (median 14,250 ft), 

high basin relief .(median 2,100 ft), and steep basin 

slopes (median 6.2 percent). 

CLIMATE 

Northern Chile is characterized by extreme aridity 

and sparse vegetation at elevations below 6,000 feet. 

This region, which includes the Coastal Range and 

Central Valley, corresponds to the approximate limits of the Atacama Desert, reputed to be the world's 

driest desert. Furthermore, the high Andes of northern Chile are extremely arid in comparison with 

other mountain ranges of equal elevation. The snowline is near 20,000 feet on the high volcanic peaks, 

perhaps the highest snowline in the world. Perennial 
ENVIRONMENT OF INTERIOR DRAINAGE BASINS 9 

snow and ice fields are found on only a few peaks 

extending above 21,000 feet in elevation. These are 

relatively small in area and in depth of snow and ice. 

The aridity is due to the cold Humboldt Current, 

which flows northward along the coast in conjunction with a counterclockwise pattern of air circulation around a permanent high far to the west, resulting in prevailing south to southwest winds along the 

coast, bringing air that has blown for great distances over the cold ocean current. Near the coast 

this air is cool and even though it may be relatively 

humid, considering its cool temperature, when it 

blows over the warm land, the relative humidity 

drops to extremely low levels. Furthermore, the· 

Andes Mountains inhibit movement of moist air 

into northern Chile from the east. 

Meteorological data for northern Chile are scanty 

and incomplete, particularly for the Andean Highlands where climatic variability is greatest. The 

more uniform climate of the coastal desert is better 

known. The most up-to-date discussion of the climate of Chile is that of Fuenzalida (1965, 1966). 

We have used these reports and an earlier report by 

the Corporaci6n de Fomento de la Producci6n 

(1950} in our attempt to evaluate the climate under 

which salars formed and continue to form in northern Chile. 

The estimated relation between mean annual precipitation and elevation for several parts of the 

region have been plotted graphically (fig. 4). AI .. 

though average temperature varies from region to 

region, the main curve (solid line) in figure 4 represents an estimated average for the entire region of 

closed basins. The interrelation among mean annual 

temperature, precipitation, and rate of evaporation 

has been explored by Langbein (1961), and data 

from his report have been used to estimate the relation between potential evaporation and elevation as 

shown in table 1. 

PRECIPITATION AND TEMPERATURE 

Coastal Range and Central Valley.-The driest 

region is a narrow strip along the coast where mean 

annual precipitation, which increases southward, 

ranges from about one-twentieth of an inch in Arica 

to about one-sixth of an inch in Antofagasta, and is 

about an inch in Taltal (Fuenzalida, 1966, table 1). 

Here, as elsewhere in the Coastal Range and Central 

Valley, rainfall may occur as infrequently as only 

once every 5-10 years. The Coastal Range is only 

slightly less arid than the immediate coast, even 

though it rises above the inversion associated with 

the cold coastal waters (Weischet, 1966). 

The Coastal Range is characterized by heavy winter (May-September) fogs known as camanchaca. 

The fog blows in over the coast, appearing as a solid 

overcast, generally several hundred feet above 

ground level, but frequently reaching the ground at 

night, and extending roughly to the elevation of the 

highest peaks of the Coastal Range. The fog may 

extend inland as far as 50 miles, an area that encompasses all the salars in the Coastal Range and Central Valley. Precipitation of fog moisture on the 

ground surface has promoted the formation of a 

nodular surface that characterizes the perennial 

rock-salt crusts of this region. Only rarely do the 

fogs extend eastward across the Central Valley and 

up to elevations of 5,000-6,000 feet along the Andean 

front. At times, condensation of water from the fog 

is heavy, being sufficient to moisten soil surfaces, to 

trickle down car windshields, and to accumulate as 

films and tiny pools in depressions on asphalt road 

surfaces. 

The lowest part of the Central Valley, where large 

salarsw f!ccur, is somewhat drier than the Coastal 

Range,; and average annual precipitation may be less 

than one-tenth of an inch. Mean annual precipitation 

for the Central Valley as a whole, from the latitude 

of Taltal to Arica, is probably less than one fourth 

of an inch. 

Compared with other deserts of the world, the 

Atacama Desert is characterized by relatively low 

mean annual temperature, about 60°F, 5°-15° cooler 

than the mean annual temperature of most other 

deserts. Summer temperatures are even more 

anomalous, daytime temperatures being about 20°F 

cooler than those in most deserts. Winter temperatures are mild, generally dropping to freezing during winter nights at the east side of the Central 

Valley only at elevations above 5,000 feet. Therefore, 

the Atacama Desert, in spite of being the world's 

driest desert, is probably one of the world's mildest 

deserts in terms of temperature extremes. 

Atacama Basin and vicinity.-The Atacama Basin 

and vicinity have a climate more humid than that of 

the Central Valley but more arid than the Andean 

Highlands. Furthermore, the climates of the western 

and eastern rims of the basin, even at the same elevations, differ markedly. The western side is 

extremely arid, whereas the eastern side is semiarid. 

Because of its large size, the Atacama Basin has its 

own unique microclimate, sufficiently distinct to create a prominent pattern on high-resolution infrared 
10 

17,000 

13.00T 

12.000r 

tu 

w 

LL 

11.000r 

10,000 

~ 9,000 

z 

0 

~ 8,000 

> w 

...J 

w 

6,000 

5,000 

4,000 

3,000 

. 2,000 

1,000 

GEOLOGY OF SALARS, NORTHERN CHILE 

Andean Highlands of northeastern 

part of Atacama Province 

Andean Highlands of Tarapaca 

and northern Antofagasta 

Provinces 

I 

/ / / I 

Andean Highlands of eastcentral part of Atacama 

Province 

/' I I 

~--------------------------~~~ /, I /// ___ ..,..,.,."" I l / --- , /---- / ... ..,-- ~ ... ~/ 

;' ,; ------------------- / -~ ..... ------------~---------, L."" _/----- - Andean Highlands of east-

- -/ central part of Antofagasta 

/ 

/ 

/ 

/ 

/ Province 

Vicinity of Atacama Basin, but excluding the basin in which Salor de Atacama ond llano de Ia Paciencia are located 

Estimated average conditions for all regions of interior surface 

drainage, including the Andean Highlands, Atacama Basin, 

Central Valley, and coastal Range 

Approximate conditions in the Pica area 

(after Dingman and Galli, 1965, fig. 4) MEAN ANNUAL PRECIPITATION, IN INCHES 

0 2 4 6 8 10 1214 

(Regional trends, without considering 

local variations; all within closed 

drainage basins; very approximate 

estimate) 

2 3 

INDEX OF POTENTIAL EVAPORATION 

0 10 203040506070 

16,000 

~ 14,000 

12,000 

~ 10,000 

z' 8,000 

0 6,000 ~ ~ 4,000 

w 2,000 

0 

\ \ 

'\\ 

/~ 

7 

7 

II 

,.,__ 

-

' \ \ 

\ I 

~~~ 

20 3040 50 60 70 

-

f".,..t'-

MEAN ANNUAL PRECIPITATION 

INDEX OF 

POTENTIAL 

EVAPORATION 

MEAN ANNUAL 

TEMPERATURE 

MEAN ANNUAL TEMPERATURE, °F (VERY APPROXIMATE) 

5 6 7 8 9 10 11 12 13 

MEAN ANNUAL PRECIPITATION, IN INCHES 

FIGURE 4.--Estimated relation between elevation and mean annual p1·ecipitation in five regions of northern Chile. 
ENVIRONMENT OF INTERIOR DRAINAGE BASINS 11 

radiometer imagery made from an earth-orbiting 

satellite. On the basis of interpretation of this 

imagery, the thermal regime of the basin is estimated to be comparable in many aspects to that of 

Death Valley, Calif., though somewhat cooler. Temperatures at night are probably cooler on the floor 

of the basin than on the surrounding slopes, and on 

these slopes temperatures are undoubtedly much 

warmer than on the high rims and adjoining highlands. 

In general, closed basins in and around the Atacama Basin are estimated to have a mean annual 

precipitation ranging from 0.6 to 2 inches. The 

mean annual temperature is estimated to range from 

47°F to 58°F, probably averaging about 52°F (table 

1). 

Andean Highlands.-The climate becomes progressively cooler and less arid toward the east as. 

elevation in the Andes increases. The heaviest rainfall is in the northernmost Chilean Andes near Peru, 

and rainfall decreases southward to the east-central 

part of Antofagasta Province and then increases 

again towards the south. In northern Tarapaca 

Province, precipitation is largely during the summer 

months of December to March; in Atacama Province 

it is during the winter months of May to September. 

At elevations of about 12,000 feet, the mean annual 

precipitation probably averages about 8 inches, but 

the lower marginal parts of the Andean Highlands 

receive much less precipitation. In the north, precipitation is rain from convectional storms in the 

summer months, but snow may fall in the high 

mountains, generally above 14,000 feet, and may 

account for as much as one-third of the total precipitation of some basins. Winter precipitation in 

Atacama Province is largely snow. Precipitation is 

extremely variable from year to year at a given 

place; commonly, wet years have two or three times 

as much precipitation as dry years. 

A factor in the climate of this region which is 

difficult to evaluate in terms of overall basin precipitation is the amount of snowfall. The highest 

peaks may receive co~siderably more precipitation 

than might be inferred from the graph (fig. 4). 

Furthermore, a large percentage of the snow that 

falls at high elevations, as well as that falling during the winter months at lower elevations, evaporates directly rather than melting to form runoff. As 

a consequence, plants are much sparser in these 

areas than would be expected. This is particularly 

noticeable in the region of Salar de Maricunga, 

which appears to be one of the driest areas of the 

Andes, even though precipitation is probably greater 

than it is to the north in Antofagasta. 

In general the interior-drainage basins of the 

Andean Highlands are estimated to have a mean 

annual precipitation ranging from 3 to 15 inches, 

and probably averaging about 8 inches. Mean annual 

temperature in individual basins in the Andes is 

estimated to range from 27°to 46°F, probably averaging about 36°F. 

EVAPORATION 

Very little information is available about rates of 

evaporation in northern Chile. At Maria Elena,· a 

nitrate plant in the Central Valley, evaporation of 

brines in large shallow tanks averages about 85 

inches annually. Brines evaporate less readily than 

fresh water, which is used in pan evaporation measurements (Harbeck, 1955, p. 1). A rough comparison 

with evaporation in the Atacama Desert is afforded 

by such measurements in the driest deserts of the 

United States. For example, lake or free-water 

evaporation at Yuma, Ariz., has been measured as 

approximately 77 inches annually, whereas pan 

evaporation in Death Valley, Calif., averages more 

than 120 inches per year (Kohler and others, 1959). 

Langbein (1961, p. 3) devised a method for estimating mean annual lake or free-water evaporation 

from known values of mean annual temperature and 

mean annual precipitation. He presented curves 

showing the correlation between these factors and 

net evaporation, defined as "the difference between 

gross evaporation and precipitation on the lake," 

and therefore a measure of the rate of removal of 

water from a closed lake. These curves were utilized 

to estimate the relative rates of potential evaporation or evaporativity in closed basins in northern 

Chile. The resulting values serve as the index of 

potential rates of evaporation (shown in table 1) in 

different basins on the assumption that humidity, 

radiation, cloudiness, and wind are equal in each 

basin. That such an index is applicable to basins in 

northern Chile is indicated by the fact that among 

the 100 largest closed basins, the five that contain 

relatively large perennial lakes rather than salars 

are among those having the 14 lowest indices (table 

1) . On the other hand, only fair correlation was 

found between the presence of lakes and the factors 

of low temperature or high precipitation when they 

were considered separately.' 

In general, the potential rate of net evaporation 

from a free water body in the Atacama Desert is 

estimated to be about 60 inches annually, although 
12 GEOLOGY OF SALARS, NORTHERN CHILE 

the rate may be considerably higher in some areas 

of exceptionally low relative humidity such as at 

Maria Elena. An annual rate of 60 inchEls is somewhat lower than in other deserts of the world. For 

example, pan evaporation in the deserts of Iran, as 

reported by Krinsley ( 1970, p. 49), has been measured as 84 inches per year at Tabas and 134 inches 

at Varamin (30 miles southeast of Tehran). 

WIND 

Very little direct meteorological data are available regarding surface wind speeds and directions in 

closed basins of northern Chile. The general movement of air is from west to east across the region, 

but local and seasonal variations are great. Probably 

the best available evidence of dominant wind directions in most closed basins can be obtained by a 

study of wind erosional and depositional features 

visible in aerial photographs. Such features are visible on or adjacent to at least 80 percent of the salars 

in northern Chile and locally are clear enough to 

provide a detailed pattern of wind variations. 

Measurement of wind directions at 40 salars resulted in the following conclusions : 

1. Over the Coastal Range and Central Valley 

strong prevailing winds are from the west, but 

towards the coast they are more likely to be 

from the southwest. At the Mejillones Peninsula, north of Antofagasta, winds are predominantly from the south or south-southeast. 

2. In the Andean Highlands and Atacama Basin, 

strong prevailing winds are from the northwest or west-northwest, and locally from the 

west. 

3. Westerly winds evidently prevailed during the 

Quaternary, as indicated by asymmetrical development of shorelines of former lakes, which 

are commonly most prominent around the 

eastern and southeastern margins of salars. 

This is presumed to result from wave action 

due to prevailing westerly to northwesterly 

winds. 

The entire region of northern Chile is characterized by extraordinary wind action. Within this 

region are at least two areas with outstanding accumulations of windblown sand, one in the vicinity 

of Pica and the other at the northern end of Salar 

de Atacama (Dingman, 1967; Dingman and Galli, 

1965). We experienced a sand storm of 2-days' duration in June 1967 at San Pedro de Atacama. At 

times, wind velocities probably exceeded 60 mph. 

During one exceptionally strong wind blast, the rear 

window of our small truck was smashed by winddriven pebbles. At the same tim_e, the sand and dust 

in the air reduced visibility to a few feet, making it 

impossible to drive a car along the road. 

REGIONAL GEOLOGY 

Most of the closed basins in northern Chile formed 

as the result of late Tertiary to Holocene faulting, 

and fault movement has affected the configuration of 

salars and the morphology of their crusts. In .ieneral, 

the major subregions containing salars are closely 

related to major tectonic elements of northern Chile. 

The Coastal Range and Central Valley subregion 

(fig. 2) is within a zone of intensive block faulting 

associated with uplifting of the Coastal Range. The 

Atacama Basin and vicinity subregion lies to the 

east and partly within a fault zone trending northnortheast, associated with the uplifted tectonic block 

of Cordillera Domeyko. The Andean Highlands subregion is in the western Andes, an area of intensive 

volcanism and faulting during the late Tertiary and 

Quaternary. 

Northern Chile is underlain chiefly by marine sedimentary rocks, volcanic rocks, and plutonic rocks of 

Jurassic and Cretaceous age, which are most widespread in the Coastal Range, and by rhyolitic to 

basaltic volcanic rocks of Tertiary and Quaternary 

age, which are most widespread in the Andean Highlands. Extensive areas are covered with thick alluvium and lacustrine sediments of late Tertiary and 

Quaternary age. 

COASTAL RANGE 

Rocks exposed in the Coastal Range are chiefly 

marine sedimentary rocks and andesitic volcanic 

rocks of Jurassic and Cretaceous age that have been 

intruded by granitic batholiths of Late Jurassic to 

Cretaceous age. Basement rocks of Paleozoic age are 

expos,ed in places, chiefly in the region west of the 

Rio Loa. The stratified rocks have been gently folded 

and intensely faulted. Rhyolitic volcanic rocks of 

probable late Tertiary age are present locally. Hills 

and valleys in the Coastal Range are extensively 

covered with unconsolidated sediments that were 

derived largely from nearby bedrock. Alluvial fill in 

some basins is more than 100 feet thick. 

An unusual feature of the Coastal Range that was 

originally described by Darwin as early as 1846 

(Darwin, 1876, p. 302) is the widespread hard surficial layer consisting of relatively pure saline material, chiefly halite, or of saline-cemented regolith. 
REGIONAL GEOLOGY 13 

A widespread mantle of reddish windblown silt and 

sand, probably volcanic ash, has also been described 

(Brtiggen, 1950, p. 142; Segerstrom, 1964, p. 163) ; 

this material occurs at places in the Central Valley 

and contributes to the reddish-brown color of many 

of the salars in this region. 

Two major sets of faults can be observed in the 

Coastal Range. The principal faults trend north and 

the others east. Many of the valleys and the closed 

basins are structural features on these faults. A 

large fault apparently extends northward along the 

coast of northern Chile, and the steep cliff on the 

ocean side of the Coastal Range is an eroded fault 

scarp. The Atacama fault, the most prominent fault 

in northern Chile, can be traced for about 350 miles, 

from near Taltal to Iquique (fig. 1). It disrupts the 

salt crust of Salar Grande, intersecting the west edge 

of the salar at the old salt quarry of Salina Rio Seco 

(fig. 13). South of this quarry the fault trace is 

marked in solid rock salt by subdued scarps and sag 

depressions that generally have relief of only a few 

feet. At another salt quarry, Salina Guanillos (fig. 

13), a fault trending west-northwest has produced a 

prominent scarp 30-40 feet high (fig. 5). 

Faulting appears to have had a profound effect on 

the hydrology and morphology of the Salar Grande 

basin. A field investigation and study of aerial photographs resulted in the following observations and 

conclusions. Formerly the basin must have been 

hydrologically closed, or nearly so; otherwise the 

solid halite body, as much as 560 feet thick, could not 

have accumulated by gradual evaporation. However, 

at present it has subsurface drainage, as indicated 

by the absence of ground water in the salt and in the 

alluvium below the salt. The salt and alluvium were 

FIGURE 5.-Fault scarps and a sag basin in massive rock 

salt at Salina Guanillos, western border of Salar Grande; 

basin in foreground resulted from solution of rock salt 

below an alluvial cover. 

penetrated by holes drilled during the 1920's in a 

search for potassium salts. Depressions having the 

appearance of solution pits or sinkholes occur near 

the eastern edge of the salar and may be sites of subsurface solution and collapse at places where ephemeral streams formerly drained into the salar. Large 

depressions at the western edge of the salar appear 

to be sag basins on faults. At places, the western side 

of the salar is characterized by abruptly truncated 

slopes ranging from less than a foot to about 30 feet 

high, which may be due to faulting and solution of 

salt. Scalloped perimeters of fans along the western 

margin, with local patterns reminiscent of a bird'sfoot delta, apparently are alluvial fans along recent 

fault scarps. 

CENTRAL VALLEY 

The Central Valley has a thick fill of unconsolidated sediments ranging in age from middle Tertiary to Holocene. This fill consists of piedmont 

alluvial deposits of silt, sand, and gravel as well as 

playa and lacustrine sediments. These deposits, 

penetrated by an exploratory oil well near the east 

side of Salar de Bella Vista (fig. 1), are about 1,300 

feet thick; they rest on older (probably Jurassic or 

Cretaceous) bedrock (Mordojovich, 1965). The uppermost layers of this 1,300-foot sequence of sediments, commonly several hundred feet thick, were 

described by Taylor (1947b, p. 26) as unconsolidated 

Pleistocene and Holocene stream deposits of _interbedded gravel, sand, silt, and clay that make up the 

great alluvial fans of the Pampa del Tamarugal. 

Much of this part of the sequence may consist of 

mudflows. Dingman and Galli (1965, p. 74-75) 

stated that the underlying older sediments are apparently semiconsolidated and fairly permeable, 

consisting chiefly of "intercalated soft sandstone, 

siltstone, and clay with occasional beds of conglomerate." These deeper sediments beneath the Central 

Valley are generally considered correlative with the 

Altos de Pica Formation (probably late Tertiary 

age) that is exposed to the east at elevations generally above 5,000 feet. Part of the overlying, more 

coarsely clastic unconsolidated sediments also may 

be equivalent in age to the upper part of the Altos 

de Pica Formation, which consists mainly of torrential and mudflow deposits (Segerstrom, 1964, 

p. 165). 

Along the western edge of the Pampa del Tamarugal the salar crusts and clay playa or lake sediments lap onto older rocks of the Coastal Range. 

Along this edge the valley fill is locally no more than 
14 GEOLOGY OF SALA,RS, NORTHERN CHILE 

50 to 100 feet thick. Sediments are presently being 

deposited in the lowest parts of the Central Valley 

by infrequent floods from the Andes. Salar crusts 

also are being formed .locally by evaporation of 

ground water. In contrast, farther north, where 

there is through-flowing drainage (fig. 2), sediments 

of the Central Valley are being eroded. 

The Central Valley originated as a tectonic depression that is thought to be Pliocene to Quaternary in 

age. It is apparently a graben, bounded by northtrending faults to the east and west that are largely 

covered with valley fill. Downwarping or monoclinal folding evidently has contributed to the formation of the valley (Brtiggen, 1950, p. 157). 

The Central Valley in Tarapaca appears to have 

been tilted westward in late Pleistocene or Holocene 

time so that the lowest part of the valley is adjacent 

to the Coastal Range. The location of the flat salar 

crusts in this area indicates that the tilting has continued · until recent times, resulting in nearly all 

clastic sediments from the Coastal Range being incorporated into the salar crust or gradually buried 

beheath its encroaching edge. In addition, the largest 

salars, Salar de Pintados for example, are lowest 

along their western sides, indicative of tilting since 

the salars first started to form. In many places along 

the eastern sides of Salar de Pintados and Salar de 

Bella Vista are broad surfaces partially dissected by 

shallow channels draining westward. These surfaces 

are interpreted as old parts of the salars that have 

been uplifted and tilted towards the west. 

Five or more separate topographic basins within 

the Central Valley are attributable partly to faulting 

and partly to development of large alluvial fans 

where major valleys drain from the Andes. The basin 

of Salar de Pintados appears to be separated from 

that of Salar de Obispo to the north by a large alluvial fan built from Quebrada de Tarapaca (near lat 

20°S.). Salar de Pintados and Salar de Bella Vista 

both seem to be bounded on their lower, southern 

edges by faults of probable Holocene age, trending 

approximately N. 50°W. and nearly west, respectively. These faults account for the resistant ridges 

of impervious ·older rocks, salients of the Coastal 

Range, that extend into the Central Valley. The 

ridges inhibit subsurface and surface drainage between these salars and between Salar de Bella Vista 

and Salar de Sur Viejo (fig. 1). 

ATACAMA BASIN AND VICINITY 

The Atacama Basin is a major structural basin 

occupying more than 5,000 square miles. The basin 

is bordered and underlain by upper Paleozoic to 

Cretaceous rocks and filled with Tertiary to Holocene continental sediments. Deposition of alluvium, 

saline deposits, and playa sediments continues. 

An interior basin first originated in early Tertiary 

time and received terrestrial clastic sediments and 

evaporites that are now well exposed iri a prominent 

ridge, the Cordillera de la Sal, which separates the 

Llano de la Paciencia from Salar de Atacama (fig. 

11). These rocks belong to the San Pedro Formation of early Tertiary age and consist of interbedded fine-grained clastic sediments, gypsum, and rock 

salt (Dingman, 1962). The salt beds are described 

(Dingman, 1962, p. D94) as "apparently the result 

of redeposition and further concentration of the 

evaporite salts from the Jurassic ( ?) and Cretaceous 

formations .. " The San Pedro Formation has been 

deformed into plunging anticlinal folds and domes, 

including salt domes. Concentric banding, attributed 

to the deformed beds of this formation, is visible 

locally in the floors of Salar de Atacama and the 

Llano de Ia Paciencia, near the south end of the 

Cordillera de Ia Sal. 

The present Atacama Basin probably formed in 

the late Tertiary (Pliocene) or early Pleistocene in 

response to the final uplift of the Andes. It postdates deformation of the San Pedro Formation. Diatomites were deposited in lakes that occupied the 

basin at one or more times during the late Tertiary 

or Pleistocene. Some diatomites on the east side of 

the basin are about 1,000 feet above present salar 

level, indicating either a former extremely deep 

lake, or more probably, that the basin has 

tilted westward and slowly subsided during th~ 

Pleistocene. 

The western rim of the Atacama Basin is formed 

by the Cordillera Domeyko, made up chiefly of the 

Purilactis Formation, of Cretaceous age, which consists of coarse conglomerate and sandstone as well 

as "fine-grained red-bed sediments and evaporite 

deposits typical of deposition in continental basins 

under arid conditions" (Dingman, 1962, p. D94). 

Intrusive granitic rocks of Jurassic to Cretaceous 

age and marine sedimentary rocks of Jurassic age 

are exposed near Salar de Punta Negra in the Cordillera de Domeyko (Chile Inst. Inv. Geol., 1968, geologic map of Chile). The eastern side of the Atacama Basin is covered largely by volcanic rocks, of 

which major components are rhyolite ash-flow tuffs. 

These deposits, equivalent in age to the Altos de 

Pica Formation, slope uniformly 3°-5°W. (Dingman 

and Lohman, 1963, p. C69). The above-mentioned 
REGIONAL GEOLOGY 15 

diatomites are younger than these volcanic rocks. 

The configuration and crustal morphology of several salars in this subregion reflect the influence of 

geologic structure. The gradual subsidence of the 

Atacama Basin was apparently accompanied by upward tilting on the east. Among the effects of this 

are: (1) crowding of Salar de Atacama and Llano 

de la Paciencia against the western edge of the basin 

(fig. 11) ; (2) crowding of salt crusts, former lakeshores, and piedmont alluvial slopes in the same 

direction; (3) presence of the area of most frequent 

flooding, sometimes termed Laguna de la Sal (Taylor, 194 7 a, p. 14, map) , in the southwestern part of 

Salar de Atacama; (4) the apparent diminishing in 

height of terrace scarps around salt crusts toward 

the west; and ( 5) presence of Quaternary lake sediments including diatomites along the eastern side 

of the basin, high above the level of the present salar. 

Other basins and salars in the vicinity show a 

similar asymmetry. For example, Salar de Punta 

Negra (fig. 6) is close to the northwestern margin 

of its basin, near a probable fault zone trending 

north-northeast. The asymmetry of the salar is interpreted as resulting in part from gradual tilting of 

the basin downward toward the northwest as the 

result of fault movement. 

ANDEAN HIGHLANDS 

The Andean Highlands are underlain predominantly by volcanic flows, tuffs, and breccias ranging 

from Pliocene to Holocene in age. The older volcanic 

rocks, equivalent in age to the Altos de Pica Formation, are chiefly of rhyolitic composition and are 

thought to have erupted from fissures and volcanic 

centers no longer evident. The younger volcanic 

rocks are chiefly andesitic to basaltic and are associated mainly with volcanic cones or stratovolcanoes. 

In some regions, however, ash-flow tuffs are among 

the youngest volcanic rocks. Locally, ridges and hills 

consisting of Jurassic and Cretaceous sedimentary 

and volcanic rocks and Cretaceous plutonic rocks rise 

above the surrounding terrain of younger volcanic 

rocks. 

There are reportedly about 800 volcanoes in northern Chile (Zeil, 1964, p. 199) ; more than 30 of these 

are between 19,000 and slightly more than 22,000 

feet in elevation. Most date from the Pleistocene, 

although a few were probably active during the 

Holocene. Only a few now show fumarolic activity. 

The Andean front in northern Chile rises eastward from the Central Valley, either as a gentle 

incline or as a s.eries of steps, and is covered by 

piedmont alluvial deposits and mudflows in the 

lower region and volcanic tuffs and flows in the 

upper region. Deep valleys, which drain westward 

across the Andean front, expose underlying rocks 

of Jurassic and Cretaceous age. 

Because most of the northern Chilean Andes are 

within the region of interior drainage, most of the 

erosional products of the region have remained within the closed basins. Sedimentary basin fill includes 

alluvium, lake and playa sediments, salines, windblown soil, and volcanic ash. 

Many of the basins in the Andean Highlands appear to be due to faulting. Examples of salars whose 

configurations seem to be partly controlled by faults 

or by fracture systems are Salar de Surire, Salar de 

Pajonales, and Salar de Coipasa (figs. 8, 11). Much 

of the eastern perimeter of Salar de Surire is out. 

lined by a series of springs that seem closely alined 

along an intersecting system of fractures or faults. 

Boiling springs and geysers, probably on a fault, 

were observed in the southeastern part of the salar 

(fig. 7). The western margin of Salar de Coipasa 

has one or more thermal springs that may also be 

on a major fault or fracture zone. The hot waters in 

both these areas are probably rela.ted to late Holocene volcanic activity. 

Many of the salars in the Andean Highlands are 

asymmetrically situated in their basins and show 

asymmetrical zoning of the saline crusts because of 

faulting and tilting of basins during Quaternary 

time. Salar de Pedernales, Salar de Maricunga, and 

Salar del Guasco (fig. 6) are among those showing 

the clearest asymmetrical patterns. All three of 

these basins appear to have been tilted downward 

to the northwest as the result of movement along 

faults trending north to northeast. They are along a 

north-trending zone of intense block faulting near 

long 69°W. Harrington (1961, p. 180) reported the 

presence of at least nine large reverse faults in the 

region immediately west of Salar de Pedernales. Two 

or more faults cross this salar, trending generally 

northeast, and one of these, the Chapapote fault, 

may be associated with oil seeps and brine-pool 

springs in the northern part of the salar (Harding, 

1926, p. 797, 799). A fault probably extends northeastward across the basin of Salar de Maricunga, as 

indicated by the pronounced elongation of the southern part of this salar and the straight southeastern 

edge (fig. 6). A major fault zone probably extends 

along the western edge of Salar del Guasco (figs. 6, 

9). Five separate north-trending narrow basins of 
16 GEOLOGY OF SALARS, NORTHERN CHILE 

--

-

0 5 MILES L____j 

0 5 MILES L____j 

Drainage-basin border 

Hard evaporite crusts, predominantly 

massive to silty rock salt (chloride 

zone) 

Soft, moist saline soil, sub ject to 

flooding; chiefly sulfate zone, containing gypsum and some halite 

• Lakes or areas frequently flooded 

EXPLANATION 

-

-

0 5 MILES L___j 

Slightly elevated marginal zone of solar, 

characterized by shallow stream channels 

and shorelines of former lakes; generally 

contains abundant gypsum 

Former solar or lokebed, apparently above 

the level of present flooding or ground-water 

evaporation; includes deltas, shorelines, 

and beaches of former lakes 

FIGURE 6.-Asymmetrical zoning of salars and drainage basins in northern Chile, attributed in part to faulting and tilting of basins. Numbers keyed to table 1. 
CLAY PLAYA SURFACES AND SALAR CRUSTS 17 

FIGURE 7.-Boiling spring and pool at southeastern edge 

of Salar de Surire. 

interior drainage occurring within 6 miles west of 

this salar are probably fault valleys parallel or subparallel to the major fault at the western border of 

the salar. 

CLAY PLAYA SURFACES AND SALAR CRUSTS 

Maps showing types of salar and clay playa surfaces (figs. 8-12) are based on interpretation of 

aerial photographs, supplemented by field reconnaisance of about 20 of the salars. More detailed 

maps were made of 28 of the salars ; five maps are 

shown as examples in figures 13-15. It was found 

that in many cases subtle differences between crustal 

types are more clearly visible in aerial photographs 

than on the ground. However, only the more general 

categories were identifiable from photographs alone 

without the benefit of a field check. Nine crustal 

types were mapped in the salars in northern Chile; 

however, intermediate crustal types can be recognized and could be shown in more detailed maps than 

we made in this study. Several of the crustal types 

are based on terminology suggested by Neal and 

others (1968, p. 74). 

Two major crustal types can be recognized in the 

salars: (1) perennial hard crusts, which are permanently dry or infrequently flooded, and (2) soft 

crusts or saline soils which generally have nearsurface ground water of comparatively low saline 

content and are subject to frequent flooding and (or) 

leaching by rain ; crusts of the latter type may be 

either perennial or ephemeral. These two crustal 

types are distinguished in the maps of salars shown 

as figures 8-12. At most salars, the hard evaporite 

crusts are roughly equivalent to the zone of chlorides, 

whereas the soft crusts are roughly equivalent to the 

zone of sulfates, which in the Chilean salars consists chiefly of gypsum, mirabilite (or thenardite), 

and ulexite. 

Other minerals are comparatively rare in Chilean 

salars. Glauberite and aphthitalite have been reported in Salar de Pintados (Gale, 1918; Pedro Alvear, oral commun., 1962). We found considerable 

amounts of calcium carbonate (aragonite or calcite), evidently of lacustrine origin, in Salar de 

Ollagiie. Trona (sodium carbonate) is rare in the 

Chilean salars, although Vila ( 1953) reported thin 

layers of trona in several salars in the Andes of 

eastern Antofagasta Province, including the following salars shown in figure 11 : Tara, Puj sa, Quisquiro, and Laco. Small amounts of the newly described mineral hydroglauberite occur in association 

with mirabilite in Salar de Pintados (Ericksen and 

Mrose, 1970, p. 14). 

CLAY PLAYAS 

Size analyses and physical properties were determined for samples of playa clastic materials and lake 

sediments, as well as dune sand and beach gravels at 

or near several salars in northern Chile. The results 

of these determinations are listed in table 2, and sizegradation data are shown in figure 16. 

Clay playas consist predominantly of clay, silt, and 

fine sand, and have surfaces ranging from hard and 

compact to somewhat soft. A small playa in the 

southern part of the Central Valley near the railroad station of Lacalle (fig. 10) might be termed a 

typical dry-clay playa, but the sediments are predominantly clayey silt rather than clay. Clastic sediment is deposited periodically on some parts of this 

playa by infrequent floods, whereas other parts are 

being eroded, having gullies as deep as 10 inches. 

The playa surface is marked by mud-crack polygons 

of a nonoriented type (fig. 17). A sample of the 

upper 4 inches of the playa (sample 19, table 2) 

consists of clayey silt (soil type ML), which, after 

leaching of soluble salt, consists of 43.2 percent silt, 

40.5 percent clay, and 16.3 percent fine sand. This, 

sample contained 4.0 percent water-soluble salt, 

chiefly halite. The surface is somewhat soft, as can 

be noted from the sunken vehicle tracks in figure 17. 
18 GEOLOGY OF SALARS, NORTHERN CHILE 

TABLE 2.-Gradation characteristics and physical 

[Soil type (Unified Soil Classification System): CL, clay of low plasticity; ML, 

poorly graded sand; SW, well-graded sand. 

Playa or lake 

clAy 

Playa silt 

Playa sand 

Dune sand 

Beach sand and 

gravel 

Terrace Sand 

(various 

components) 

.. 

., 

.a 

8 

" = 

., 

-a 

s 

.. 

r:Jl 

52 

48 

19 

208 

62 

92 

88 

91b 

99 

101 

20 

37 

98 

102 

36 

Sample identification, location 

! 8 .. ~ = ;a 

-a. .. .. 0 

.. 8 8 

-;; .. .. .. " .... ~ :a 0 "" ., :l .. .. s "" 1>0 .. ., 2 z ~ c 

Salar near 0-10 24°15'S. Rosario. 70° 02'W. Salar del 25-50 23 ° 38'8. Carmen. 70 ° 17'W. 

Playa near 0-10 24 °28' 8 . Lacalle. 69 °51'W. 8alar Mar 0-10 23°48' S. Muerto. 69° 49'W. Salar near 0-10 24°17' S. 

Imilac. 68•so·w. Salar de 30 19°39'S. Obispo. 69•56'W. 

Salar de 0-10 21 ° 13'8. Llamara. 69•33'W. 8alar de 25-30 20 ° 26'8. Pintados. 69°43'W. 8a!ar de 0-10 2'0 °38'8. 

Coposa. 68 ° 37'W. 

Salar del 0-10 20°17'8. Guasco. 68°49'W. 8alar de 0-10 21 °19'8. 

San Martin. 68° 18'W. 

8alar de 0-10 21°13'8. 

O!lague. 68 ° 19'W. 

8alar de 0-10 20°41'8. Coposa. 68•86'W. 

Salar del 3-10 20 ° 15'8. Guasco. 68•52'W. Salar de 0- 10 21 °13'8. Olla&'Ue. 68° 19'W. 

Depth to the water table is unknown but is probably several tens of feet, or more. 

A dry-clay playa south of Oficina La Joya (fig. 1) 

is several square miles in area and is thought to be 

the largest dry-clay playa in northern Chile. It differs from the playa near Lacalle in having a hardclay and silt surface marked by mud-crack polygons 

as much as 3 feet in diameter. Smaller dry-clay 

playas are found at several other places in the 

Coastal Range and Central Valley of northern Chile. 

Other dry-clay playas and areas of lake sediments 

are being eroded by gullying and by wind deflation. 

Such areas are found along the eastern edge of 

Salar de Llamara in the vicinity of Cerro Soledad 

(fig. 9; sample 88, table 2), and at Salar Mar Muerto 

(fig. 10; sample 208, table 2). Surface material in 

these areas consists of clayey silt or silty fine sand 

(soil type ML-SM) and is partially covered by a 

thin mantle of wind-rippled sand. These playas are 

estimated to be of Holocene age, representing the 

.< 

2 

"" "" .. 

t' ., 

~ 

!' ~ ·~ 

= 1>0 

0 

:;3 

~ fil 

.. " 

-~ 

"" r:Jl 

3,950 2.92 

1,700 2.85 

4,750 2.91 

2,380 2.83 

10,000 2.71 

3,500 2.62 

2,600 2.76 

3,370 2.69 

12,300 

12,400 

12,300 

12,35(1 

12,500 

12,400 

12,300 

.. 

-

.. 

~ ., 

~ 

.. 

] 

:s 

"' C' 

~ 

26.3 

29.3 

23.5 

24.9 

15.2 

29.2 

17.3 

±20.5 

Atterberg Limits 

(fraction passing 

No. 40 sieve) 

~ 

= ., 

1:! 

., 

~ 

~ :;3 " .. 

£ 

22.0 

21.5 

±21.5 

21.3 

12.2 

±27.4 

±17 

±19 

~ 

.5 "' 

!' 

'tl 

:;3 

:1 

ii: 

4.8 

7.8 

±2.0 

8.6 

3.0 

±1.8 

±0.3 

±1.5 

last episode of playa sedimentation in the basins. An 

old playa on the east edge of Salar de Llamara is 

dissected by steep-sided gullies to depths of at least 

5 feet and by wind-eroded blowouts at least 2 feet 

deep. Salar Mar Muerto is chiefly a playa that has 

been strongly dissected by gullying and wind 

blowouts. 

A clay playa in the Central Valley, several miles 

south of Salar de Obispo (fig. 8), is locally wind 

eroded; a scalloped surface has formed (fig. 18) that 

is similar to wind-eroded surfaces of other clay 

playas in northern Chile. At places in this same area, 

as shown in figure 18, the ground is covered with 

round boulders of rhyolite tuff that were derived 

from the wind-eroded playa sediments. These boulders were carried by floods from the Andes and evidently moved out onto the playa by rolling or floating 

along in sheet wash and thin mudflows. 

The environment of deposition of the eroded clay 

playa sediments was similar to the present environ-
CLAY PLAYA SURFACES AND SALAR CRUSTS 19 

properties of clastic sediments from northern Chile 

silt of low plasticity; SM, sand with appreciable amounts of silt; SP, 

From U.S. Army Corps of Engineers (1953)] 

Mechanical analysis Gradation 

(combined hydrometer and sieve) characteristics Classification 

Gravel Sand Silt Clay Diameters for 

~ (percent) (percent) (percent) (percent) given percent finer (mm.) 

1>. 

.1> 

~ -;;- s 

.. .. .~ .. ., 01 1>. ... r:l d_ .. .. _ .. r:l .. <la =:s ci "- Ei .. . :;""';' .. z ~a ~~ .. a ee 010 1\ e == .e.,.-4 :a ... ;aS :.Ceo.:~ <R..., "0 e ... "go c; .. .. .,. .,,. "o ,.,o a-=: 8 a ... 0::0 e . ..-=: '~ ~0 ~~ .L'T 11~ .. 0 ~1 ... " ~e.b ~~ , ... 5~ ..... > . "'"" """ i~ ..... """ o::": ,o r..l\ 0 • ~o =~ 8e -~o Oo c~ o.:! r..~ r..~ o~ 

6.7 0 0.9 5.2 12.5 20.9 35.6 

12.3 0 0.5 5.8 4.7 28.5 44.0 

4.0 0 0.2 16.1 24.1 19.1 14.8 

4.6 0 0.3 9.2 22.0 36.3 12.3 

8.6 0.9 15.0 28.3 16.0 13.5 8.9 

0 6.6 3.6 32.8 12.1 17.1 18.2 

1.2 0 7.2 41.8 20.1 9.9 8.8 

0 0 2.5 58.8 5.3 8.6 12.5 

0 11.0 88.0 ±1.0 0 0 

0 0 33.0 58.0 9.0 0 0 

0 12.0 48.0 34.0 ±6.0 0 0 

0 20.5 49.5 24.2 ±5.8 0 0 

0 10.6 43.8 32.8 12.8 0 0 

0 8.5 45.5 41.5 ±4.5 0 0 

0 3.0 62.5 32.0 ±2.5 0 0 

ment in the Central Valley except that runoff from 

the mountains was sufficiently great or sufficiently 

frequent to create more extensive ephemeral lakes. 

Even today, ponds or small playa lakes form at a few 

places along the western border of the Pampa del 

Tamarugal, particularly in the area between Salar 

de Pintados and Salar de Obispo (fig. 1), every year 

or two, after exceptionally heavy rains in the Andes. 

These playa lakes dry up in a few days, leaving a 

thin deposit of silt, clay, and fine sand. 

Clastic sediments are commonly found beneath the 

salt crusts of many of the salars in the Central Valley; these sediments probably were deposited during 

a former time of slightly greater rainfall in the 

mountains to the east, during which runoff was sufficient to form playa lakes. The sediments are of 

several types, as shown by samples in table 2. Silty 

clay (soil type CL) was found beneath a 10-inch 

salt crust of Salar del Carmen (fig. 10; sample 48, 

table 2), and silty fine sand (soil types ML--SM or 

~ t -;:- t 0 .. .. 1>. ~ r:l r:l <r:l <r:l 

~ " .. .. .. ·a ..~ e e ~ .. 

bO 

=e " " " .. ... ~ ... 0 <Re .. .. GJ,6 "' "' "' " 1:',... "' § .. ~g ~ 0 0 

"' ..... ~ o::!;! ~ 

.et ~ 

~ ~ :s '5-'ii r..~ >=I 1:/l oo~ 

24.9 0.{)039 0.0013 ESt. CL-ML Silty 

0.00057 clay 

16.5 .0039 .0016 est. CL Do. .0()08 

25.7 .021 .0013 est. ML Clayey 

.00034 silt 

19.9 .0099 .0035 est. ML Do. .00038 

17.4 .099 .0055 est. ML-SM Silty 

.00054 fine sand 

9.6 .085 .0047 .0010 ML-SM Do. 

12.2 0.10 . 016 est. ML-SM Do • .00071 

12.3 0.18 . 0081 est. SM Do • .00073 

0 

0 

0 

0 

0 

0 

0 

0.25 .185 .135 SP Poorly 

graded sand 

0.34 0.17 0.08 SW-SM Silty sand, 

well-graded 

2.7 0.19 0.11 SP-SM Silty sand, 

poorly graded 

3.1 0.42 0.12 SP-SM Do. 

0.87 .205 .061 SM Silty 

sand 

0.72 0.24 0.12 SP Poorly 

graded sand 

0.99 0.36 .177 SP Do. 

SM), beneath the 10-to-12-inch salt crusts of Salar 

de Obispo (fig. 8; sample 92, table 2) and Salar de 

Pintados (fig. 13; sample 91b, table 2). Very fine, 

clastic sediment collected from Salar del Carmen and 

a salar near Rosario (fig. 10) consists of 60.5 percent clay, 33.2 percent silt, and 6.3 percent sand; 

the samples also contained 6. 7 percent and 12.3 per;.. 

cent of water-soluble salts, respectively. Coarse 

playa sediments from Salar de Obispo and Salar de 

Pintados contain 25-28 percent clay, 14-30 percent 

silt, 36-61 percent sand, and as much as 7 percent 

gravel. Water-soluble salts occur in trace amounts 

only. These relatively coarse sediments probably resulted from torrential streamflow and mudflows, 

which still occasionally pour out into the Central 

Valley after especially hard rains in the Andes. 

Layers of saline material, chiefly gypsum or anhydrite, are interbedded with clay playa or lake 

sediments beneath some salars (fig. 19). These layers are either remnants of old salar crusts or layers 
20 GEOLOGY OF SALARS, NORTHERN CHILE 

EXPLANATION 

15,125 ® 

Solar or old lakebed, 

undifferentiated; most are shown 

in detail on inset maps 

Area of lakebeds and shorelines 

of former lakes 

Hard saline crusts of salars 

Soft surfaces, wet to dry, 

of salars 

Lakes or areas frequently flooded 

Jl.(I./'I.M 9 ,000-ft contour 

15,026 Mountain peak showing 

® elevation, in feet 

Number of solar and 

basin keyed to table 1 

'--'"" Divides af closed basins 

(Area of interior drainage 

is shaded) 

0 5 MILES 

I.J...J...J...U 

FIGURE 8.-Salars and basins of interior drainage in the northern part of Tarapaca Province, Chile. 
CLAY PLAYA SURFACES AND SALAR CRUSTS 

EXPLANATION 

Solar or old lakebed, undifferentiated; most are shown in 

detail on other figures 

Area of lakebeds, and shorelines of former lakes 

19,833 

®- Mountain peak showing elevation, 

in feet 

Number of solar and basin 

keyed to table 1 

~j~~~~ll\[~~f~J~\\\1 Hard saline crusts of salars \J'!NV\ 9000-ft contour 

.. 

-

Soft surfaces, wet to dry, 

of salars and playas 

Lakes or areas frequently flooded 

-- Divides of closed basins 

(Area of interior drainage 

is shaded) 

0 5 MILES I.J....u..J...J 

® 

19,554 

FIGURE 9.-Salars and basins of interior drainage in the southern part of Tarapaca Province and northeasternmost 

part of Antofagasta Province, Chile. 

21 
22 

23 

24 

GEOLOGY OF SALARS, NORTHERN CHILE 

EXPLANATION 

Solar or old lakebed, 

undifferentiated; most are shown 

in detail on inset maps 

fV!.SV.... 9 ,000-ft contour 

11ra1 

-

Area of lakebeds and shorelines 

of former lakes 

Hard saline crust, of salars 

Soft surfaces, wet to dry, of 

solars ond playao 

11,155 

® 

.... -..... 

0 5 MILES 

~ 

Mountain peak showing 

elevation, in feet 

Number of solar and 

basin keyed to table 1 

Divides of closed basins 

(Area of interior drainage 

is shaded) 

FIGURE 10.-Salars and basins of interior drainage in the western central part of Antofagasta Province, Chile. 
Salar de Aguas 

Calientes · 

0 1 MILE 1..-J 

33 

Salar de Pular 

0 1 MILE <--.J 

CLAY PLAYA SURFACES AND SALAR CRUSTS 

35 

Solar or old lakebed, 

undifferentiated; most are 

shown in detail on inset 

maps 

-

Area of lakebeds, ond shorelines of former lakes 

• Hard saline crusts of salars . 

• Soft surfaces, wet to dry, 

of salars 

-

Lakes or areas frequently 

flooded 

18,60<' Mountain peak showing 

® elevation, in feet 

e Number of solar and 

basin keyed to table 1 

/ 

/ Divides of closed basins 

0 5 MILES L..J...L.U....I 

FIGURE 11.-Salars and basins of interior drainage in the eastern central part of Antofagasta Province, Chile. 

23 
24 

0 5 MILES 

l.....u.....J 

GEOLOGY OF SALARS, NORTHERN CHILE 

-

-

13,260 

® 

G 

NV-J\ 

EXPLANATION 

Solar or aid lakebed, 

undifferentiated; most ore 

shown in detail on inset maps 

Area of lakebeds, and shorelines of former lakes 

Hard saline crusts of salars 

Soft surfaces, wet or dry, of 

sa Iars 

lakes or areas frequently 

flooded 

Mountain peak showing eleva· 

tion, in feet 

Number of solar and basin 

keyed to table 1 

9 ,000-ft contour 

FIGURE 12.-Salars and basins of interior drainage in the northeastern part of Atacama Province, Chile. 
CLAY PLAYA SURFACES AND SALAR CRUSTS 

Solors de Pintodos and Bello Vista 

EXPLANATION 

Nitrate workings at west border of salars; salt, 

sulfate, or potash mine workings in solar 

Area of vegetation or cultivation in solar; 

generally with slobby to nodular, silty halite crust 

Nodular to platy, white salt crust 

Nodular to platy, silty salt crust 

Rugged anhydrite crust 

Massive, coarsely crystalline halite 

Wind-blown sand and silt; includes salt-encrusted dunes 

in southwestern Solar de Bello Vista 

Solar Grande 

Nitrate plant 

Recent fault, marked by scarps and sag basins 

in the salt as well as alluvium 

Open pit salt mine 

FIGURE 13.-Geologic maps of Salar de Pintados, Salar de Bella Vista, and Salar Grande. Location shown in figure 9. 

25 
26 GEOLOGY OF SALARS, NORTHERN CHILE 

c 

EXPLANATION 

Undifferentiated lacustrine sediments, includes saline to gypseous soils 

Delta of former lake 

Area showing shorelines of former 

lake 

Pond or area frequently flooded 

Knobby, massive white rock salt 

0 1 MILE 

L--l 

Rugged gypsum crust 

Smooth halite flood plain 

Sulfate zone, undifferentiated; 

consists chiefly of soft moist 

gypseous soil 

Spring 

c 

Intermittent stream showing direc-

~ tion of flow 

FIGURE 14.-Geologic map of Salar de Pedernales. Location shown in figure 12. 

N 
'N 

CLAY PLAYA SURFACES AND SALAR CRUSTS 

0 1 MILE L___._J 

EXPLANATION 

Undifferentiated lacustrine sediments, includes saline to gypseous 

soils 

Delta of former lake 

Area showing shorelines of former 

lake 

Pond or area frequently flooded 

Knobby, massive white rock salt 

Sulfate zone, undifferentiated; 

consists chiefly of soft moist 

gypseous soil 

Windblown sand and silt 

Spring 

Intermittent stream showing direc-

-···----- tion of flow 

FIGURE 15.-Geologic maps of Salar del Guasco and Salar de Coposa. Location shown in figure 9. 

27 
28 

100 ~ 

90 

80 

Iz 70 w 

u 

"' w 

0. 60 IJ: 

C) 

w 50 ~ 

w 

> 

~ 40 _, 

::1 

~ 

::1 30 u 

20 

10 

0 

10 

GEOLOGY OF SALARS, NORTHERN CHILE 

Playa or lake clay, com- Dune sand, composite 

posite histogram for sam- histogram for samples 

pies 52 & 48 99 & 101 

!Z 20 w 

u 

"' w 

0. 

I- 0 

J: 

C) 60 

w Playa silt, composite Beach sand and gravel, ~ histogram for samples composite histogram 

~ 40 19 & 208 for samples 20 & 37 

z 

0 

i= 

::1 

... 

ii2 

IV) 

i5 

> 0 

u 

z 60 w Playa sand, composite Terrace sand ::1 

" histogram for samples 62, (various components), 

w 92, 88, 91b composite histogram "' ..._ for samples 98, 102, 

36 

DIAMETER, IN MILLIMETERS 

U.S. STANDARD SIEVE SIZE 

NO.4 NO. 10 N0. 40 NO. 200 

-~ ~~A-....1 0 

1-. I ~ """-! • 

\ -..,. I \ '\ ... ...._A 

l\i '\ '\ I"' ., ~ II\ \ ~ 

1 \'~ \ I\ 1\ ~ ... . ~ 

"" 1\\ I \<?, \ \ \ 'I-, 

I "" I I \ 1\C?._,. "}. ""'- \~ · 

~~ \'%1 +, -~ 

<!-- ,A ~ 1\'"~ I \II ~'I- 0, <> ~ 

~~ "'<>. <> ~ 

~'-, \C$ - I 1\"o- ..-:..~ 

"c. +.~ ~ 

I I ... o,?o- \ ~ 1\ \ 

.. jb, \_ r--r--..... 1\ 

I I I"' I +" "'-11 \\ \ r-..., ...... 

I I I ""\ \ I ..... r--..... 

\.\ 

I I ' I 

I ·erroce 

I I I l~ond 

1.0 0.1 

DIAMETER, IN MILLIMETERS 

0.01 

~ \ 

..... , \ 

~ 

............. 

'""" 

0.001 

FIGURE 16.- Histograms and cumulative curves showing size-gradation for the six types 

of clastic sediments listed in table 2. 
CLAY PLAYA SURFACES AND SALAR CRUSTS 29 

B 

FIGURE 17.-Active mud-cracked dry-clay playa near the 

Lacalle railroad station. A, Soft surface showing car 

track 1-2 inches deep. B, Surface of playa showing 

randomly oriented mud-crack polygons. 

of saline material deposited in the soil at the top of 

a temporary ground-water level. 

HARD EVAPORITE CRUSTS 

Six types of hard evaporite crusts can be recognized in the salars of northern Chile, of which five 

have very rugged surfaces and one a relatively 

smooth surface. Most of the hard crusts consist 

chiefly of halite, but a few consist of anhydrite or 

A 

B 

FIGURE 18.-Wind-eroded dry-clay playa sediments in the 

Pampa del Tamarugal several miles south of Salar de 

Obispo. A, Wind blowouts 2-3 ft deep in thinly layered 

playa sediments. B, Rounded boulders, averaging 6 in. 

in diameter, of rhyolite tuff eroded from the playa sediments. The boulders were rafted into the area by muddy 

flood waters or thin mudflows. 

gypsum. The rugged types are characteriz.ed by predominantly dark tones on aerial photographs because 

they are generally either covered by a thin mantle 

of windblown or waterborne silt and fine sand or 

contain clastic material incorporated from underlying playa or lake sediments. The smooth type appears white to light gray on aerial photographs, 

evidently because it consists of a hard perennial 

layer of relatively fresh pure salt that is not covered 

with windblown sediment. The rugged perennial 

crusts appear to be above the highest local level generally reached by flood waters, either from surface 

runoff or from rising ground-water tables, whereas. 
30 GEOLOGY OF SALARS, NORTHERN CHILE 

FIGURE 19.-Pit about 6 ft deep in clay playa near north end 

of Salar de Pintados showing layers of anhydrite, the 

white bands in lower part of pit wall. 

the smooth white crusts are subject to rather frequent, perhaps annual, flooding. Some hard crusts 

are in a state of change from smooth to rugged or 

rugged to smooth in response to changing patterns 

of flooding and consequently are gradational or intermediate types. Hard evaporite crusts evidently-cover 

more than 1,500 square miles, more than 50 percent 

of the total area of Chilean salars. This is in marked 

contrast to closed basins in the United States, for 

example, where hard evaporite crusts are comparatively rare. Although there are as many closed basins 

in the United States as in Chile, the only good examples of hard evaporite crusts are in Death Valley, 

Calif. (Devil's Golf Course and similar areas) ; the 

Bonneville Salt Flats, Utah; Searles Lake, Calif. ; 

Bristol Lake, Calif.; and possibly a few other dry 

lakes in the Mojave Desert of southeastern 

California. 

LAYERED MASSIVE ROCK SALT WITH A 

RUGGED SURFACE 

The most prevalent of the six types of hard 

evaporite crusts in the Andean region is a rugged 

perennial massive rock-salt crust deposited during 

evaporation of Quaternary lakes. These crusts are 

commonly in a relatively inaccessible setting, being 

surrounded on nearly all sides by the soft watersaturated soil of the sulfate zone. Their extremely 

rugged surfaces prevent travel by vehicle and make 

foot travel difficult; consequently, they are poorly 

known. On recent maps, made in the early 1960's 

(U.S. Air Force, Operational Navigational Charts, 

for example), many of these areas are erroneously 

shown as lakes. 

The rock salt is massive, consisting of layers of 

hard white fine-grained salt, generally more than 4 

inches thick, separated by thin layers of silty salt. 

Near the northwestern edge of Salar de Pedernales 

(fig. 14) two prominent layers within the upper 3 

feet of the rock-salt crust can be seen (fig. 20). The 

uppermost is about 10 inches thick and is separated 

by a silty parting from an underlying layer, which 

is more than 18 inches thick, extending below the 

bottom of the pit. The parting is irregular and 

probably is an old surface of the salar that was thinly blanketed by windblown silt, just as the present 

surface is. The salt crust here appears to be exceptionally thick in comparison with that of other 

salars. Layered white high-purity rock salt can be 

seen in the walls of brine pools such as the one shown 

in figure 21. The brine level here was about 2 feet 

below the salt surface at the time of our visit in May 

1967, as is shown in figure 21. Depth of this pool 

was estimated to be 25-30 feet; the vertical to overhanging walls are composed of pure white salt. The 

bottom could be seen covered with fragments of the 

salt, visible beneath the perfectly clear brine. The 

exceptional thickness of salt may result from gradual subsidence of the northwestern part of the salar, 

which is near a large fault zone, from repeated 

flooding, and from intermittent deposition of rock 

salt. The pool probably formed by solution of the 

FIGURE 20.-Layering of massive rock salt near the northwestern edge of Salar de Pedernales. The upper 10-in. 

layer of salt is separated from the underlying salt by a 

~- to l-in. layer of silty salt. 
GLA Y PLAYA SURF ACES AND SALAR CRUSTS 31 

FIGURE 21.-Brine pool in thinly layered high-purity rock 

salt in the northern part of Salar de Pedernales. The 

pool, 25-30 ft deep, is probably formed by solution of the 

crust by a recently developed fresh-water spring in the 

clastic sediments underlying the salar crust. The pinnacled surface around the pool is due to periodic (annual?) flooding as the water table rises. 

crust by water from a newly developed spring in 

the clastic sediments below the salt crust. Such a 

spring could have formed on one of the recent faults 

known to exist in this area. 

Infrequent flooding of the massive rock-salt crusts 

and periodic leaching by rainfall generally form 

extremely rugged and pitted surfaces. These surfaces may have delicate pinnacles and knobs like the 

surface near the salt pool shown in figure 21, or, 

more typically, they may be rugged and hummocky, 

as shown in figure 21 at a greater distance from the 

pool, where the surface has an average relief of 

about a foot. More rarely, the leached surface has 

an extremely irregular network of pits and knobs 

with a delicate clinkerlike texture, as shown in 

figure 22. 

SLABBY OR NODULAR SILTY ROCK SALT 

Silty rock-salt crusts consist chiefly of halite with 

varying but generally lesser amounts of clay, silt, 

and sand. They have formed by capillary evaporation of subsurface moisture that deposited salt at 

the surface and as a cement in the surface layer of 

the fine-grained clastic sediments. In this way, a 

FIGURE 22.-Rugged perennial rock-salt crust showing delicate clinkerlike texture, southeastern part of Salar de 

Atacama. 

silty salt crust forms, and deposition of salt continues by evaporation of ground water at the base 

of the crust. Silty rock-salt crusts are characteristic 

of the extremely arid Central Valley and Coastal 

Range. Typical silty crusts are those of Salar de 

Obispo (fig. 8), Salar de Pintados (fig. 13), Salar 

de Bella Vista (fig. 13), Salar de Lagunas (fig. 9), 

and Salar del Carmen (fig. 10). Similar crusts 

were seen in the northern part of Salar de Punta 

Negra (fig. 10) and at the eastern edge of Salar de 

Atacama (fig. 11). 

This type of crust consists of salt-cemented clastic 

material that commonly makes up more than 25 percent of the crust. The crusts are underlain by UTIcemented fine-grained playa and lacustrine sediments 

that appear similar in color and composition to the 

clastic material within the crust. The transition 

from hard crust to soft underlying sediment is 

abrupt (fig. 23). Although the term silty rock salt 

has been used for convenience, the clastic material 

may range from clay to coarse sand. The crust consists of a partially cemented rubble of irregular to 

polygonal slabs and nodular fragments (see fig. 39) 

that formed by breaking of the older crust as a new 

crust formed below and pushed it upwards. Thermal 

expansion and contraction in response to diurnal and 

seasonal temperature changes contributed to the 

breaking and heaving of the crust. The crust is 

generally 1-4 feet thick but locally exceeds 5 feet. 

The nodular surface is attributed in part to modification of salt fragments by winter fog, the 

camanchaca. 
32 GEOLOGY OF SALARS, NORTHERN CHILE 

FIGURE 23.-Section of slabby and nodular silty rock-salt 

crust exposed in cut along Pan-American Highway, Salar 

de Obispo. The crust is underlain by silty sand, which is 

loosely cemented by a meshwork of gypsum crystals and 

contains blebs and small nodules of white ulexite ( U). 

Salars having crusts of this type are in basins that 

formerly had ephemeral lakes in which fine clastic 

sediments and saline material were deposited. When 

the climate became more arid, the lakes dried, and 

deposition of saline minerals by ground water began. 

The water came from the Andes in sufficient quantity to maintain a near-surface ground-water table. 

The high rate of evaporation inhibited accumulation 

of surface water. Deposition of such salar crusts is 

taking place today in parts of several salars, including Salar de Pintados and Salar de Bella Vista. 

Evaporation of ground water has played a role in 

past deposition of silty rock-salt crusts in the Andes, 

as it does today, but because of flooding and washing 

by rains, such crusts tend to be ephemeral. Salar 

crusts formed by surface water and by ground water 

are believed to be extensive and intimately associated in the Death Valley salt pan, California (Hunt 

and others, 1966, p. B64), where their differentiation required detailed mapping. The two types appear to be identical in aerial photographs of that 

area, as they do in Chile. 

RUGGED GYPSUM OR ANHYDRITE 

Rugged gypsum or anhydrite crusts are exceptional types that occur in only five or six salars. They 

vary widely but appear to have the common characteristic of being composed in large part of sulfate 

minerals, chiefly gypsum in the Andes and anhydrite 

in the more arid coastal region. They are moderately 

hard and coherent. Hard rugged crusts of sulfate 

minerals in salars of the Andean Highlands are 

rare. The sulfate zones in these salars tend to be soft, 

varying from a plastic gypsum mud to a moist sand 

consistfng of subhedral gypsum crystals in areas of 

very shallow ground water, to a dry and friable, 

locally layered or laminated, very fine grained to 

crystalline gypsum meshwork in slightly elevated 

areas above the water table or capillary fringe. 

The principal occurrences of the rugged dry anhydrite crust are at Salar de Llamara (fig. 9), the 

southeasternmost end of Salar Grande (fig. 13), the 

eastern part of Salar de Pedernales (fig. 14), an 

area along the eastern edge of Salar de Atacama 

(fig. 11), and an area in the western part of Salar 

de Surire (fig. 8). 

Large areas of Salar de Llamara have a crust composed mainly of anhydrite, which has been severely 

eroded by wind into fluted hummocky forms and 

intervening irregular pits and basins that commonly 

have a relief of 5-10 feet. The resulting surface is 

the most rugged of all salar surfaces in northern 

Chile, being highly variable in both thickness and 

relief. The northern border of Salar de Llamara is 

several tens of feet higher than the central and 

southern part of the salar. Tentative conclusions regarding a possible sequence of events in formation of 

this crust, on the basis of a reconnaissance along the 

northern margin, and published information by 

Brtiggen (1950), are as follows: (1) the anhydrite 

represents the original sulfate zone (gypsum) deposited on the floor and around the edges of Gran 

Lago Soledad, a former deep lake that periodically 

may have overflowed into the basin of Salar Grande; 

(2) at a high lake level, drainage across the Coastal 

Range began and ultimately cut the present sharp 

canyon of the Rio Loa and drained the lake to the 
CLAY PLAYA SURFACES AND SALAR CRUSTS 33 

point that only a small lake remained in a subsidiary 

basin northwest of Cerro Soledad; (3) final evaporation of this lake resulted in deposition of highpurity rock salt; (4) movement on east-trending 

faults, of Quaternary age, along the northern margin of the basin caused uplifting here and tilting 

toward the south; (5) extensive erosion of the salar 

by wind deflation and gullying. 

The gypsum crust in the eastern part of Salar de 

Pedernales (fig. 14) was not seen during the present 

study, but was described by Harding (1926) as a 

severely wind-eroded remnant of a former layer, 

now consisting largely of isolated mounds containing 

large gypsum plates and crystals. It seems probable 

that the gradual tilting of the Pedernales basin, upward in the southeast with respect to the northwest, 

has elevated an old sulfate zone. Well-preserved lakeshore lines occurring in the eastern and southern 

sides of the basin, as much as several hundred feet 

above the level of the present salar, are convincing 

evidence for such tilting. A gypsum layer probably 

covered the floor and margins of the former lake 

before the deposition of massive halite. 

Part of the southeastern border of Salar de Atacama (fig. 11) consists of a rugged clinkerlike crust 

of gypsum (fig. 24) similar in appearance to the 

nearby rugged rock salt crust shown in figure 22. 

This is the only area where this type of gypsum 

crust was seen in northern Chile. The surface was 

FIGURE 24.-Rugged gypsum crust showing a clinkerlike 

texture, eastern side of Salar de Atacama. 

evidently formed by the erosion, resulting from 

rainfall and infrequent flooding, of a hard granular 

gypsum crust. The crust was exposed either as the 

result of lowering of the ground-water table or of 

tilting due to faulting. 

Another type of rugged gypsum crust, observed in 

the northwestern part of Salar de Surire (fig. 8) 

consists of a dry hard granular layered gypsum with 

a pit~ surface. Relief is on the order of 1-3 feet, 

and the surface is 3-4 feet above the main level of 

the salar, which here consists of relatively smooth 

moist gypsum sand containing nodules and lenses 

of ulexite. 

MASSIVE, COARSELY CRYSTALLINE ROCK SALT 

Massive, coarsely crystalline rock salt occurs only 

in Salar Grande (fig. 13), a salt-filled basin, shown 

by d.dll-hole core to average more than 99 percent 

halite to a depth of as much as 560 feet. The surface 

is nodular and silty to depths of 1-3 feet, appearing 

similar to some of the nodular silty halite crusts of 

salars in the Central Valley. Thenardite is present 

locally as tan subhedral to euhedral crystals as much 

as 2 inches long in irregular zones of white sugary 

salt that are distinct from the more typical coarsely 

crystalline halite of the salar. The salt in Salar 

Grande has been mined in open pits for many years 

and presently is the source of most of the salt used 

in Chile. 

The salt is cut by deep vertical joints (fig. ,25) 

that are generally spaced 5-15 feet apart and, as 

seen in the salt quarries, may extend to depths of 

more than 20 or 30 feet. Silt from the surface has 

stained the joint surfaces reddish brown. The salt 

contains abundant small fluid inclusions but otherwise is dry. Drilling during the 1920's showed the 

presence of dry cavities and porous zones to the 

bottom of the salt layer. Loss of drilling water indicated that the underlying alluvium also was dry. 

Distinctive giant oriented polygons, hundreds of feet 

across, are faintly visible in aerial photographs in 

nearly all parts of Salar Grande. These giant polygons, as well as the smaller polygons that are outlined by the above-mentioned joints in quarries, are 

not apparent on the ground, being obscured by the 

eroded nodular surface of the salar. 

SMOOTH ROCK SALT 

Rock-salt crusts that are subject to periodic flooding may become covered by a relatively smooth crust 

of freshly deposited white halite (fig. 26). In large 

part, the salt is leached from an older crust near or 
34 GEOLOGY OF SALARS, NORTHERN CHILE 

FIGURE 25.-Massive, coarsely crystalline rock salt in an 

active salt quarry, northern part of Salar Grande, showing prominent vertical joint surfaces (J) coated with silt 

and sand. 

at the site of the new smooth crust. Smooth rock-salt 

crusts generally range from a few inches to a foot 

or two in thickness. They are underlain by a sticky 

mud that inhibits subsurface drainage and tend to 

be in shallow depressions bordering older rugged 

crusts. 

This type of crust is found in the United States at 

the Bonneville Salt Flats, Utah, and in parts of the 

Death Valley salt pan, California. In these places 

the salt reportedly attains maximum thickness of 

more than 10 inches. The Bonneville Salt Flats appear to be subject to seasonal flooding, largely by 

rising ground water which is such a concentrated 

brine that it dissolves little or none of the perennial 

salt crust. Evaporation of the surface water deposits 

a thin smooth new layer of salt on the old crust. A 

halite flood plain in the Death Valley salt pan west of 

Badwater apparently is subject to less regular 

flooding, the salt probably surviving intact for periods of several years, and therefore being essentially 

perennial. 

In Chile, smooth rock-salt crusts occur in the 

northern part of Salar de Maricunga (fig. 12), in 

the western part of Salar de Pedernales (fig. 14), 

and in the southern part of Salar del Carmen (fig. 

10). Salar de Uyuni in Bolivia (fig. 1) consists largely of a smooth rock-salt crust, which extends over 

an area of many hundreds of square miles. This 

crust, which is commonly 10 feet or more in thickness, owes its smoothness to annual flooding by a 

rising ground-water table and annual deposition of 

a thin layer of salt. During the dry season, trucks 

can cross this salar at high speed in almost any 

direction. 

The flooding of salars may originate from surface.. 

water runoff, from a rise in the water table, or both. 

The salt is initially flat, but as it dries it may form 

polygons (fig. 26) or sharp pressure ridges (fig. 

27). It tends to become rough with age if periodic 

flooding does not occur, as a result of cracking due 

to thermal expansion and contraction, and of weathering. The smooth salt crust in the southern part of 

Salar del Carmen (fig. 27) weathered over a period 

of 5 years (1962-1967) into scattered nodular fragments. This was attributable largely to condensation 

of fog. 

SILTY NITRATE-BEARING SALAR CRUST 

An unusual type of salar crust that is probably 

unique to the Atacama Desert of northern Chile, is 

one containing soda-niter (NaN03) as a significant 

FIGURE 26.-Smooth rock-salt crust in flood plain, northwestern part of Salar de Maricunga. Salt crust is about onehalf inch thick; newly formed salt polygons have upturned 

edges as much as 5 in. high. 
CLAY PLAYA SURFACES AND SALAR CRUSTS 35 

FIGURE 27.-Pressure ridges in newly deposited thin (1-2 

in.) layer of white sa}t, southern part of Salar del Carmen. 

saline constituent. Five salars in the region have 

been mined as a source of commercial nitrate: 

Salar de Lagunas, Salar de Pampa Blanca, a small 

unnamed salar just north of Sierra Gorda, Salar del 

Carmen, and another small unnamed salar near 

Oficina Rosario (figs. 1, 9, 10). The content of sodium nitrate in these salars ranges from a few percent 

to about 25 percent; those parts of the salars that 

were mined probably had average grades of 10-20 

percent NaNOs. The crusts contain considerable silt 

and sand from underlying sediment, thus resembling the more typical silty rock-salt crusts of other 

salars in the region; they also contain halite and sulfate minerals, including thenardite and gypsum, as 

part of the saline cement. Samples 48 and 52 (table 

2) show the nature of the clastic material in the area 

of nitrate workings at the salar near Oficina Rosario 

and at Salar del Carmen. The saline complex of nitrate-bearing salars resembles the more normal 

nitrate caliche of this region in containing small 

amounts (a f ew hundredths to a few tenths of a percent) of perchlorate (Clo4-) and iodate (IOn. 

The silty nitrate-bearing crusts resemble the silty 

rock-salt crusts but tend to have smoother surfaces. 

They generally are not more than a few feet thick, 

and the richest nitrate ore is commonly in the upper 

part of the crust. Figure 28 shows mine areas in the 

southern parts of Salar del Carmen and of Salar de 

Pampa Blanca. Fragments in the ore piles at Salar 

B 

FIGURE 28.-Silty nitrate-bearing salar crust. A, Shallow 

nitrate workings in the southern part of Salar de Pampa 

Blanca. B, Piles of nitrate ore in the southeastern part 

of Salar del Carmen. 

del Carmen were tested in the field and were estimated to contain as much as 20 percent NaN03. 

Salar del Carmen was mined periodically during 

the later part of the 19th century; according to people familiar with the nitrate industry (Frank H. 

Humberstone, oral commun., 1962), the nitrate ore 
36 GEOLOGY OF SALARS, NORTHERN CHILE 

in areas that had been mined would regenerate itself 

in 5-10 years. Evidently regeneration involved capillary migration of ground water and evaporation 

to deposit NaNOa in the upper part of the crust and 

on the surface. 

The above-mentioned salars are in closed basins ; 

some of these basins have extensive nitrate deposits 

on the hillslopes surrounding the salar (Salar de 

Lagunas, Salar de Pampa Blanca, and the small 

salar near Oficina Rosario), whereas Salar del Carmen is at the terminus of a transverse valley that 

drains the area of extensive nitrate deposits northeast of Baquedano (fig. 1). These salars probably 

differ in composition from others in northern Chile 

because they represent deposition from ground waters containing saline materials leached from nitrate deposits. Saline minerals, including nitrates, 

are still being deposited in Salar del Carmen and 

Salar de Lagunas which have near-surface ground 

water, but not in the other three salars, which are 

dry and in which the water table is at depths of 

20 feet or more. 

SOFT SURF ACES OR CRUSTS 

MOIST SALINE SOIL 

Soft moist salar surfaces occur in parts of salars 

that are subject to flooding by surface water and 

that have a shallow fluctuating ground-water table 

that keeps the surface moist. Underlying sediments 

tend to be permeable moist to water-saturated silts 

and sands, rather than relatively impermeable muds. 

The surfaces of these salars contain only small 

quantities of saline minerals. On aerial photographs 

these surfaces generally appear dark gray to black, 

commonly showing smooth bands of differing shades, 

indicating different degrees of soil saturation. The 

moist soils are characteristic of the lowest parts of 

Andean salars, which are subject to frequent flooding. During the rainy season, and for a few weeks 

or months thereafter, these areas are likely to be 

shallow lakes. Evaporation and decrease in groundwater levels expose the moist soils during the dry 

season. However, some areas of deeper water in 

Andean salars tend to be covered with water during 

most if not all the year. Such areas are really perennial or intermittent lakes. 

A good example of a soft moist soil surface is in 

the central part of Salar de Maricunga (fig. 12). In 

May 1967, the time of our visit to this locality, this 

entire area was flooded by shallow water, as was a 

part of the smooth halite flood plain to the north. 

This temporary lake disappears partly or entirely 

during each dry season, whereas ponds at the southern end and southeastern edge of this salar appear 

to be perennial. 

MOIST GYPSEOUS CRUST 

Moist to water-saturated crusts containing a large 

percentage of gypsum are widespread in Andean 

salars. They are the dominant crustal type of some 

salars such as Salar de Ascotan (fig. 9), and in others form the bordering zones around hard evaporite 

crusts of rock salt. The gypseous zone commonly contains moderate amounts of halite and mirabilite 

either as surface incrustation or admixed with the 

granular gypsum in the crust. Nearly all the gypseous crusts of the Andean salars contain disseminated fibers, blebs, nodules, and layers of ulexite; at 

several salars this ulexite has been mined from shallow pits such as those shown in figure 29. 

The soft gypseous crust generally is made up of a 

loose accumulation of tan to cream-colored subhedral gypsum crystals of sand size. The gypsum is 

moist to within a few inches of the surface, and the 

saturated zone is generally within 10 or 20 inches of 

the surface. The surface is smooth to hummocky, 

with a microrelief of as much as 3 or 4 inches. The 

bearing strength is variable, ranging from an extremely soft surface impossible to cross with a 

FIGURE 29.-Soft gypseous crust underlain by a 10-20-in. 

layer of high-purity ulexite that was mined in shallow pits 

now filled with water, Salar de Ascotan. The pond is 

about 10 ft wide. 
FEATURES OF SALAR CRUSTS IN CHILE 37 

4-wheel drive vehicle, to a compact surface that can 

be crossed by car. A typical example of this type 

of crust is the eastern side of Salar de Punta Negra 

(figs. 10, 30). A similar crust on the western side of 

Salar de Surire (fig. 8) is 18 inches to 3 feet thick 

and is underlain by reddish-brown moist to watersaturated silt and clay. 

Some of the soft gypseous crusts also may contain 

small amounts of sodium or calcium carbonate. For 

example, Sayes (written commun., 1968) found 

that marginal zones of Salar del Guasco and Salar de 

Coposa (fig. 15) contained carbonates, sodium bicarbonate being prevalent in Guasco and calcium 

carbonate in Coposa. 

Practically all the salars in the Andean Highlands 

· appear to be bordered by crusts of this type on one 

or more sides. The crust tends to be much better 

developed on one side than the other, an asymmetry 

attributable either to basin tilting or to greater inflow of water on one side of the salar than on the 

other. 

DRY FRIABLE CRUSTS 

Soft dry friable crusts are characterized by a porous, puffy surface consisting of fine-grained clastic 

sediments and varying but generally considerable 

amounts of halite and gypsum and lesser to trace 

amounts of other saline minerals such as ulexite and 

thenardite. The upper few inches are typically composed of a loose dry powder covered by a very thin 

crust which is easily crumbled in the fingers. At 

depths of 8-10 inches the soil tends to be moist and 

contains relatively little saline material. The surface 

is evidently kept in a puffy condition by crystallizaFIGURE 30.-Soft moist gypseous crust, eastern side of Salar 

de Punta Negra. 

tion of salts in the capillary fringe of the water table 

and by periodic leaching of the salts by rainwater or 

by flooding ; these factors inhibit formation of a 

hard salar crust. 

A small salar near Imilac, north of Salar de Punta 

Negra (fig. 10), is typical of this type of crust. 

Parts of the crust show evidence of being smoothed 

by recent flooding, and others show transitions between such a surface and the typical puffy surface. 

The upper 6 inches of soil from this salar (sample 

62, table 2), after leaching, was found to consist of 

26.3 percent clay, 29.5 percent silt, 43.3 percent 

sand, and 0.9 percent gravel. The unleached sample 

contained about 9 percent water-soluble salts. This 

crustal type also is extensive around the eastern edge 

of Salar de Atacama (fig. 11), where it may be the 

remnant of a marginal sulfate zone that has dried 

because of a decline in the water table. 

FEATURES OF SALAR CRUSTS IN CHILE 

Northern Chile offers unique opportunities for 

study of morphological and structural features that 

form in salt crusts in response to unusual climatic 

and hydrologic environments and to fault movements in an active seismic region. Such structural 

features appear to be more varied and better shown 

in the Atacama Desert and the Andean Highlands 

than in other deserts of the world, and some of the 

features may be unique to this area. Because of the 

extreme aridity of the Atacama Desert, rock salt 

tends to be relatively stable; in most other deserts, 

salt that is deposited during an annual dry season 

tends to be washed away during the following wet 

season. Not only are perennial rock-salt crusts widespread in the Atacama Desert, but soils generally 

contain a high content of halite, gypsum, and sodaniter. Furthermore, this is one of the few areas of 

the world where rock salt is sufficiently stable to 

make a satisfactory building stone, and hygroscopic 

saline soil, a good ro!ld-surfacing material. Building 

walls constructed of rock salt or saline-cemented soil 

(saline caliche) may remain standing, with little 

change, for 50 years or more. 

In spite of the very arid climate, salar crusts of 

the Atacama Desert are in a state of gradual but 

continual change. Agents operating to bring about 

these changes are (1) surface water, (2) ground 

water and springs, (3) rainwater and fog, (4) faulting and fracturing, and (5) wind action. Examples 

of morphological and structural features that are 

recognizable in aerial photographs are shown in 

figure 31. 
38 GEOLOGY OF SALARS, NORTHERN CHILE 

H 

K 

FIGURE 31.-Distinctive patterns observed on aerial photographs 
A 

8 

c 

• D , ' r:: .!-£0 & E ~o;~ 

;§ P'&. F 

G 

K 

L 

M 

N 

p 

Q 

R 

s 

T 

u 

v 

w 

X 

y 

z 

San Martin (W) 

Atacama (N E;) 

Atacama (NW) 

Pampa de Tara (E) 

Grande (7, fig. 9, E) 

Llano de Ia Paciencia 

Pedemales (W) 

Tolar (NW) 

Pedemales (W) 

Atacama (N) 

Atacama (SE) 

Atacama (S) 

Atacama (S) 

Atacama (SE) 

Atacama (SW) 

Pedemales (S) 

Guasco (NE) 

Pintados (SW) 

~:ii~~>tes(33' fig.ll, SE) 

Tara (E) 

Laguna de Tuyajto (E) 

Grande ( 7, fig. 9, SE) 

~.fli~~tes (31, fig. 11, W) 

Ollagiie (SW) 

lnr::aguasi (NW) 

FEATURES OF SALAR CRUSTS IN CHILE 

Crenulate ~norgins, concentric bands; 

evaporite crust, salt channels. 

Crenulate margin; hard evaporite crust. 

Poolt ringed by white saline soil; hard 

evaporite crust. 

Polygons in tuff(?) swept bare by wind. 

Polygons in faulted, exceptionally thick 

massive rock salt. 

Poly~ns in Miocene evaporites(?) exposed in solar. Polygons in very thick massive rock salt(?). 

Polygons in smooth fresh white salt crust. 

Polygons in old hard evaporite crust, probably rock salt. Same as I; both I and J show on photographs 

as li ht networks on dark salt. 

Vegetation along old solar shores; hard evap- orite crust of rock salt. Vegetation along spring-fed moist zones. Vegetation along old solar shores, probable 

spring zones. Marshy vegetation around springs; vegetation 

cross-hatched. 

Wind-blown salts on solar; polygons (crosshatch pattern) simi lor to F above. 

Wind-blown salts (gypsum?); old delta shaded. 

~':'.,~\'."dinal dunes and barchans (enlarged in 

Dust lobes on salt. 

Former lakeshores; old channe Quisquiro nearby. Former lakeshores, at north partly obliterated by wind. Former lakeshores; old delta cross-hatched, newer delta hashured. 

Old drainage channels(?) buried by salt. 

Remnants of hard evaporite cruat{?l. Remnants of hard evaporite crust(? ; 2 wind 

directions(?). 

Eroded and corroded margin of hard evaporite 

crust, salt channels. 

EXPLANATION 

D 

Soft, moist saline soi I of solar, subject to 

flooding; chiefly sulfate zone containing 

gypsum and some halite 

Predominantly clastic sediment, including 

alluvium, and lacustrine sediments; also 

consolidated or semiconsolidated sediments 

(all areas other than salars) 

Hard evaporite crusts, 

-

predominantly massive to silty rock salt (chloride zone) 

Ponds, open water; 

-

frequently flooded 

areas 

of salars and basins of former lakes in northern Chile. 

39 
40 GEOLOGY OF SALARS, NORTHERN CHILE 

FEATURES DUE TO FLOODING BY 

SURFACE WATER 

SALT CUSPS AND CRENULA TE MARGINS WITHIN 

SALARS 

Rugged rock-salt crusts that abut against younger 

smooth rock-salt crusts generally have crenulate 

margins (fig. 31A, B) consisting of intersecting 

cusplike curves that are concave toward the younger salt crust. Borders of this type may be highly 

irregular, having a dendritic form such as in figure 

31B, but commonly they are more regular. This type 

of salt interface shows clearly in aerial photographs. 

It forms by corrosion of older salt and redeposition 

of new salt by floodwaters, the flooding generally 

resulting from a gradual rise in water level. The 

younger salt, which is in an area of periodic flooding, 

forms a slight depression, whereas the older salt, 

which is slightly above flood level, is slowly corroded; solution and gentle wave action apparently 

combine to produce a cuspate crenulate interface 

between the two types of salt. 

Salt cusps and crenulate margins are found in 

nearly all salars of the Andean Highlands that have 

a rugged perennial rock-salt crust. They are well 

developed in the north-central part of Salar de Atacama (fig. 31B) where the points of the intersecting 

cusps are typically 10 to 50 feet apart in the most 

strongly crenulate margins and 100 to 200 feet apart 

in those more gently crenulate. Good examples of 

crenulate margins can also be seen in aerial photographs of Salar de Punta Negra, Salar de Pedernales, and Salar de Maricunga. In the United States, 

a similar crenulate "pattern" can be seen around 

the margin of the Devils Golf Course, Death Valley, 

Calif. 

SALT CHANNELS 

Rugged rock-salt crusts that are immediately leeward of springs or ponds in regions of strong prevailing winds are likely to have lobate margins in 

which parallel or subparallel channels, floored with 

fresh white salt, extend into the rugged crust (fig. 

31A, Z). Such channels are commonly hundreds or 

even thousands of feet long. We have termed them 

salt channels. They result largely from corrosion of 

the older salt by windblown water. 

Salt channels of this type are best developed at 

the western margin of Salar de Incaguasi (fig. 11) 

where there are many prominent southeast-trending 

channels, the two largest being 2 miles long and 

100- 500 ft wide (fig. 31Z) . Salt cusps and crenulate 

margins occur at places in the salt channels, being 

best developed at the leeward ends of the channels. 

Salt channels also can be seen in aerial photographs 

of Salar de Ia Isla (fig. 12), and small or incipient 

salt channels can be seen in several other salars in 

the An~ean Highlands. 

Salt channels are believed to indicate: (1) strong 

prevailing winds, (2) large flows of spring water 

having only low to moderate salinity, (3) presence 

of a rugged perennial rock salt crust that is above 

flood level or otherwise protected from flooding, and 

( 4) proximity of the rugged salt crust to the windward side of the basin, with little or no development 

of a bordering sulfate or carbonate zone. 

SALT PSEUDOBARCHANS 

As interpreted from aerial photographs, an old 

rugged salt crust in the western part of Salar de 

Aguas Calientes (fig. 31X) is in an advanced stage 

of corrosion by windblown surface water, the remnants of the former crust being characterized by 

rounded cuspate forms, which in aerial photographs 

appear to have the form of barchan dunes. We have 

called them salt pseudobarchans. They appear to be 

surrounded on all sides by fresh white salt that is 

periodically flooded. Flow lines and shallow channels 

in the white salt curve around the windward sides 

of the ps~udobarchans and trail off to leeward. The 

pseudobarchans appear dark in the photographs, 

indicating that they have a mantle of windblown 

silt and sand. Crenulate margins at leeward edges 

that were corroded by standing water and smoothly 

rounded windward edges that were corroded by 

windblown water indicate that the pseudobarchans 

are remnants of an old salt crust. 

Salt pseudobarchans are not known to occur elsewhere in Chile and may be unique. However, dunelike forms along the southern edge of Salar de Ollagiie (fig. 31Y) appear to be partly the remnants 

of a hard evaporite crust and partly dunes of clastic 

saline material, mainly gypsum, and silt. 

The pseudobarchans in Salar de Aguas Calientes 

are thought to be due to strong winds, somewhat 

variable from west to northwest, to large flows of 

spring water from the western margin of the salar, 

and to presence of a crust of perennial rock salt 

that is being corroded. 

SALT BLISTERS 

Newly deposited thin layers of rock-salt crust 

locally form blisterlike mounds as the result of ex-
FEATURES OF SALAR CRUSTS IN CHILE 41 

pansion of the salt layer during crystallization and 

drying. Typical salt blisters are shown in figure 32. 

The blisters are a variation of pressure ridges that 

also form in newly deposited thin salt layers, as 

shown in figure 27. 

Salt blisters are found at many places in the Andean salars of Chile. They are undoubtedly common 

to seasonally flooded salars elsewhere. Hunt, Robinson, Bowles, and Washburn (1966, p. B6&-B66) described blister crusts in the Death Valley salt pan, 

California. 

GYPSEOUS RAMPARTS 

Saline ponds along the western edge of Salar de 

San Martin (fig. 31A) are rimmed on the east by a 

low ridge that consists chiefly of hard nodular finegrained gypsum (fig. 33), which we have termed a 

"gypseous rampart." This ridge separates the ponds 

from the soft gypseous crust of the salar to the east. 

The rampart is 10-20 feet wide and is 2--5 feet high, 

being highest near the pond edge, and slopes gently 

eastward to the level of the gypseous crust, which 

during the dry season is a few inches to about a foot 

above the level of the pond. 

The rampart formed by evaporation of windblown 

spray from the pond that was carried by the prevailing westerly winds. Other salines, chiefly halite, are 

also deposited from this spray but are leached by 

seasonal rains. 

FEATURES FORMED BY GROUND WATER 

AND SPRINGS 

SALT CASCADES AND SALT TERRACES 

Near the head of Rio Salado, 25 miles northeast of 

Potrerillos (fig. 1), are found unique cascades and 

FIGURE 32.-Salt blisters on rock-salt flood plain, northern 

end of Salar de Maricunga. Newly deposited salt layer 

is '4-lh in. thick; hollow blisters shown are as much as 

6 in. high. 

FIGURE 33.-Gypseous rampart (maximum height of 4 ft) 

bordering saline pond at western edge of Salar de San 

Martin. Inset photograph shows the nodular character 

of the hard fine-grained gypsum, which is the chief saline 

component of the rampart. 

terraces of rock salt. Here, the stream valley is 

within 1,000 feet of the border of Salar de Pedernales (fig. 12), and the valley floor is about 300 feet 

lower than the brine level in the salar. Brine springs 

on the valley wall, fed by subsurface seepage through 

permeable strata and along fractures in a probable 

fault zone have deposited salt on the side and bottom of the valley. This natural flow has been augmented by a higher level, manmade tunnel, apparently driven to increase the water flow into the Rio 

Salado. The salt cascades are along the steep side of 

the Rio Salado valley; on the floor of the valley 

are constructional salt terraces, reminiscent of hotspring deposits (fig. 34). A copious flow of brine can 

be heard flowing in salt tunnels beneath the terraces, 

in spite of the fact that the manmade tunnel was 

closed at the time of our visit. 

The water level within the adjoining part of the 

salar is approximately 3 feet below the surface of 

the salt crust. The decline in water level in this area, 

presumably since construction of the tunnel, must 

have been at least 1 foot, as indicated by horizontal 

shelves of fresh salt in the sides of a trench. 

BRLVE POOLS 

Perennial circular pools 3-30 feet across occur in 

salars of northern Chile where springs of relatively 

fresh water have dissolved holes in a salt crust and 
J 

42 GEOLOGY OF SALARS, NORTHERN CHILE 

FIGURE 34.-Sait cascades and constructional salt terraces 

at the eastern side of the valley of Rio Salado, near the 

northwestern corner of Salar de Pedernales. 

maintained them against the growth of new salt 

from the sides (fig. 21). The pools are most common 

near the margins of perennial rock-salt crusts, where 

they are thought to be maintained by springs in permeable layers at the foot of adjoining piedmont 

slopes, and along faults below the crusts. 

Many well-developed brine pools, thought to be 

along faults, are in the northwestern part of Salar de 

Pedernales. The largest pools (fig. 21) are as much 

as 30 feet wide and 30 feet deep, having vertical to 

overhanging walls of white rock salt clearly visible 

beneath the brine. Smaller brine pools, 3-15 feet 

across, occur along the eastern edge of Salar de 

Atacama (fig. 35). They are apparently associated 

with fresh-water springs supplied by subsurface flow 

from the large alluvial fans to the east, or along a 

fault zone in this area. The pools are in a marginal 

zone having a thin hard rock-salt crust overlying 

water-saturated plastic gypseous clay. The crust 

around the pools is smoother and whiter than the 

surrounding crust (fig. 35), indicative of seasonal 

flooding. 

SALT CONES AND CUPS 

Among the most unusual salt structures found on 

salar crusts in the northern Chilean Andes are salt 

FIGURE 35.-Small brine pool in a thin, 1-2 ft rock-salt crust, 

eastern side of Salar de Atacama. 

cones, of which typical examples are shown in figure 

36. Salt cones are best developed on perennial rocksalt crusts where the ground-water table is within 

the crust and near the surface. They are centered 

over salt-solution tubes (fig. 40) leading down to the 

ground-water table. The best examples seen in the 

present study were in the northwestern part of Salar 

de Pedernales, where three general types can be observed, as shown in figure 36. Here, the water table 

was only about 2 feet below the surface of the salt 

crust at the time of our visits in May 1967, which 

was near the end of the dry season. Low salt rims, 

the vestiges of salt cones, surround vertical tubes on 

the perennial salt crusts of Salar de Atacama and of 

Salar de Pintados. 

The salt cones at Salar de Pedernales are as much 

as 8 inches high and 10 inches in diameter at the 

base and have walls as much as an inch thick. They 

consist of granular to fibrous halite. Specimens of 

thick-walled cones, examined in the laboratory, appear to consist chiefly of microscopic elongated, 

twisted, interwoven fibers of halite. The fibers tend 

to be rather uniform in diameter and are of roughly 

the same dimensions and gross appearance as the 

fibers in bond paper. The salt cones are solid closed 

structures (fig. 36B), cones with a small opening on 

the top, or more open structures such as that shown 

in figure 36C. An intermediate type, such as figure 

36A, may have a subsidiary opening on the side. 

Cones, once formed, may later be partially eroded or 

corroded so much that only a vestige of the cuplike 
FEATURES OF SALAR CRUSTS IN CHILE 

A 

B c 

FIGURE 36.-Salt cones on rugged perennial rock-salt crust in the northwestern part of Salar de 

Pedernales. A, Rugged rock-salt crust typical of area; enlarged inset is of complex cone, shown 

in photograph, which has a breached top and tubular side opening. B, Salt cone in an early 

stage of development. C, Remmant of salt cone, a salt cup. 

43 
44 GEOLOGY OF SALARS, NORTHERN CHILE 

A 

B 
FEATURES OF SALAR CRUSTS IN CHILE 45 

base, which may be filled with windblown sediment, 

remains. 

The mode of formation of the cones we saw in 

Chile in 1967 was not clear because all were fully 

developed cones or cuplike remnants. However, in 

November 1970, Ericksen found cones in Salar de 

Pocitos, northern Argentina (fig. 1), that showed a 

complete sequence of cone formation and destruction. 

This sequence is shown in figure 37. The cones 

start to form as nodular veinlets of moist granular 

salt within polygons in rock salt, as is shown in 

figure 37 A. These veins form in cracks resulting 

from diurnal expansion and contraction of the salt 

crust. Capillary rise of brine, which stands only 

about 2 feet below the surface, deposits the salt in 

the veins and causes the nodular efflorescences on 

the surface. These veins do not form at the margins 

of the polygons where diurnal expansion is greatest 

and where thin lacy sheets of salt (fig. 37A) may be 

squeezed out, making a rim around the polygon. Certain of the nodules continue to grow by capillary rise 

and deposition of salt from brine, forming a solid 

nodule of moist granular light-gray salt a few inches 

in diameter and height. At some point in this growth 

c 

FIGURE 37.-Above and facing page. Formation of salt cones 

at Salar de Pocitos, Argentina. A, Nodular salt veins in 

salt polygons, the first stage of development. Note thin 

lacy sheets of salt squeezed upwards along polygon 

borders because of thermal expansion. B, New salt cone 

formed by growth of a nodule on one of the salt veins. C, 

Breached salt cone, the final stage of development. 

stage a small tube (fig. 38) forms in the vein, extending from brine level to the cone, and a white 

cap of dry salt appears on the top of the cone shortly 

thereafter. 

Once the tube forms, the cone continues to grow by 

both capillary rise of ground water and diurnal 

pumping, wherein moist air moves out of the tube 

(and cone) during the warm day, and dry air moves 

into them during the cold nights. These processes 

cause the cone to expand (fig. 37B), eventually to 

become thin, and finally to develop openings at one 

or more places. Generally a simple opening forms on 

top of the cone (fig. 37C). While the cone grows, 

the tube below it increases in diameter to as much 

as 5 inches in large cones. Finally, an open cuplike 

structure forms (fig. 36C). 

FIGURE 38.-Salt saucers at Salar de Pocitos, Argentina, 

that result from corrosion of salt polygons by rainwater. 

Note hole of salt tube (T) at site of former salt cone and 

salt network (SN) in center of breached saucer. Also note 

salt pond in upper left of photograph. 
46 GEOLOGY OF SALARS, NORTHERN CHILE 

Cones apparently form in a few weeks or a few 

months. Those shown in figure 37 were destroyed 

during the rainy season a few months after these 

photographs were taken, and their former presence 

is indicated only by the open tubes in the salt polygons. 

Dingman (1963) described delicate salt cups on 

rock-salt beds of Tertiary age in the hills of the 

Cerros de la Sal between Salar de Atacama and the 

Llano de la Paciencia (fig. 11). Like those seen in the 

salars, these cups are centered over tubes leading 

downward into the salt. Dingman attributed formation of these cups to movement of moist air out of 

the tubes. 

Hunt, Robinson, Bowles, and Washburn (1966, p. 

B62) reported delicate efflorescences of salt (incipient salt cups?) around tubes leading downward into 

the salt crust in the northern part of the Badwater 

Basin, Death Valley, Calif. These authors attribute 

the efflorescences to escape of moisture from underlying sediments through the tubes. During a visit in 

1968, Stoertz found several small active salt cones 

in the Death Valley salt pan, about 2 miles southwest 

of Badwater. 

FEATURES FORMED BY SOLUTION OF SALT BY 

RAINWATER AND FOG 

SALT SAUCERS 

Salt saucers are salt polygons that have a pronounced concave form and a prominent rim. They 

occur in Salar de Obispo (fig. 8) and other salars in 

the Central Valley in places where the crust of 

slabby and nodular silty rock salt is 1-3 feet thick. 

The saucers, which form a network, are generally 

5-10 feet across, and their upturned rims range 

from 6 inches to about 2 feet in height (fig. 39). The 

saucer rims are commonly outlined by nodular rock 

salt, whereas the centers of the saucers are relatively 

smooth and consist of polygonal plates of silty rock 

salt 1-3 feet in diameter. 

These salt saucers are pressure-ridge polygons 

that were leached by rain and fog, which dissolve 

surficial salt and carry it down into the rather porous 

silty crust. Loose silt and sand remaining at the 

leached surface is blown away by wind. Redeposition of salt from the surface and deposition of new 

salt by capillary evaporation of ground water at the 

base of the crust probably cause additional expansion of the salar crust and elevation of the saucer 

rims. Thermal expans.ion and contraction, due to 

diurnal temperature changes, open cracks that allow 

movement of salt into the crust and also expand 

and lift the polygonal plates. 

FIGURE 39.-Salt saucers in slabby and nodular silty rock 

salt, Salar de Obispo. 

Another type of salt saucer, shown in figure 38, 

formed by corrosion of polygonal salt cakes by rain. 

This type of saucer is characteristic of relatively 

thin salt crusts having abundant salt tubes and salt 

cones. Rainwater, which drains through the tubes, 

corrodes the polygon first to the saucerlike shape and 

then dissolves away the lowest part of the saucer 

(fig. 38), finally destroying it. Upturned edges of 

the saucers in part are due to cementation of extruded salt that had formed at polygon borders (fig. 

37A, 38). 

SALT NODULES 

Rounded forms or nodules of salt are widespread 

and abundant in the soils and salars of the Coastal 

Range and Central Valley of northern Chile. They 

have formed by slow solution and recrystallization 

on surfaces of salt fragments, chiefly due to fre-
FEATURES OF SALAR CRUSTS IN CHILE 47 

quent wetting by the nightly winter fogs. Rainfall is 

so infrequent and sparse in this region that it little 

affects the formation of salt nodules. The nodules 

range from an inch or two to about a foot in 

diameter. 

Two types of salt nodules can be distinguished. 

One type, as shown in figure 40A, forms from hard, 

dense, crystalline rock salt, and the other, shown in 

figure 39, forms from the porous silty salt typical 

of most salar crusts of the Coastal Range and Central Valley. In the first type, the fog condensate 

collects as a thin film on a relatively impermeable 

rock-salt fragment, dissolves a little salt, and then 

flows downward on the sides of the fragment where 

it evaporates and reprecipitates the salt as a sugary 

white porous mass. As can be seen in figure 40A, 

this new salt collects on the bottom and sides of the 

fragment. In a final stage it grows over the top, 

completely enclosing the remains of the original salt 

fragment. It is estimated that the fragments shown 

in figure 40A lay undisturbed for more than 30 years. 

Other fragments in this same area that were broken 

during salt mining in the 19th century are completely covered with white sugary salt, and some fragments less than 5 or 6 inches in diameter lack a crystalline salt core. 

The nodules form in a slightly different way from 

porous silty salt. Fog condensate moistens the porous surface to depths of one-tenth of an inch or 

more, and dissolved salt moves into the fragment. 

Removal of the salt cement leaves loose silt on the 

surface that is carried away by wind. The nodule 

tends to be less porous than the original silty fragment. The end product is a white nodule of granular 

salt similar to that formed from the dense crystalline 

salt described above. 

Ultimately the salt nodules are destroyed by fog 

and rain, the salt being slowly dissolved and carried 

down into the soil. This process is accelerated where 

hygroscopic saline minerals are present in the salt. 

It has been particularly effective in destruction of 

fragments of hygroscopic nitrate ore at mines in 

this area, fragments as much as a foot in diameter 

being completely dissolved in a few tens of years. 

Their former presence is now revealed by small piles 

of loose rock fragments and sand, the former matrix 

of the ore. 

SALT PINNACLES 

In the Andes, perennial rock-salt crusts that are 

infrequently flooded commonly are covered by a 

variety of jagged forms such as pinnacles and serrate ridges. These forms are characteristic of most 

perennial rock-salt crusts in the Andean Highlands 

and Atacama Basin, where flooding generally takes 

place only during exceptionally rainy years. These 

rugged crusts have a different appearance from the 

rounded nodular crusts typical of the Central Valley 

and Coastal Range. The pinnacles result from corrosion by rain, commonly windblown rain, as evidenced by the orientation of points and ridges in the 

general direction of the prevailing strong winds. 

Pinnacle height ranges from 1 to about 6 inches and 

is a rough measure of time since the last flooding. 

The surface of the massive rock salt in the northwestern part of Salar de Pedernales (fig. 14) shows 

typical well-developed pinnacles ranging from about 

2 to 5 inches in height (fig. 40B). Salt pinnacles are 

also shown in figures 21 and 36. 

Jagged or pinnacled surfaces seem best developed 

in areas of thick rock salt on the largest salars, 

which are well drained, so that flooding is rare and 

crustal modification is largely or wholly by rainwater. 

SALT SOLUTION TUBES 

Massive rock-salt crusts in the Andes contain salt 

solution tubes through which rainwater drains (fig. 

40C). The tubes are characteristically found in the 

lowest parts of relatively smooth basinlike depressions, which generally range from a few feet to 10 

or 15 feet in diameter. They appear to have formed 

by drainage of rainwater that would otherwise collect in small shallow pools after rains. The tubes are 

generally not more than a few inches in diameter. 

They are nearly vertical, straight to curving, and 

lead down at least to the water level in the salt crust, 

which may be at a depth of as much as several feet. 

Salt solution tubes are particularly numerous and 

widespread in the northwestern part of Salar de 

Pedernales in an area that is relatively smooth, evidently having been flooded more recently than the 

surrounding rugged crust. In this part of the salar, 

many solution tubes are in areas of more rugged 

rock-salt crust (less frequently flooded) and are 

capped by salt cones or cups (fig. 36). Solution tubes 

also occur in Salar Grande, where there is no known 

water table and where they are presumed to drain 

downwards to interconnecting fissures that extend 

to great depths and serve as channelways for subsurface drainage of the basin. Dingman (1963) described salt tubes as occurring in the massive rock 

salt of the Cordillera de la Sal where they are also 

associated with salt cups. 
48 GEOLOGY OF SALARS, NORTHERN CHILE 

A c 

B D 

FIGURE 40.-Features formed by solution of salt by rainwater and fog. A, Salt nodules forming from fragments of 

coarsely crystalline rock salt, Salina Guanillos, west side of Salar Grande. B, Salt pinnacles in massive rock-salt 

crust, northwestern part of Salar de Pedernales. C, Orifice of a salt solution tube about 4 in. in diameter (at top 

of arrow) in relatively smooth massive rock-salt crust, northwestern part of Salar de Pedernales. Arrow indicates 

direction of surface flow of rainwater. D, Salt stalactites on overturned slab of rock salt, eastern side of Salar de 

Atacama (pen gives scale). 

SALT ST ALACTITFS 

Cavities in salar crusts may contain stalactites 

such as those in the eastern part of Salar de Atacama (fig. 40D). Here, salt stalactites one-half of an 

inch in diameter and as much as 6 inches long are 

widespread. They are found beneath an upper layer 

of somewhat porous rock salt at the margin of the 

salar, and can be seen only by prying up individual 

polygonal cakes. Salt stalactites undoubtedly are 

present elsewhere in the crust of this salar and in 
FEATURES OF SALAR CRUSTS IN CHILE 49 

the rock-salt crusts of other salars in northern Chile. 

They also have been found at a few places in cavities 

in the nitrate ore of the region. Salt stalactites occur 

in Death Valley, Calif. (Hunt and others, 1966, p. 

BllO), on the overhanging edges of salt saucers in 

the flood plain west of Badwater. 

The stalactites are formed by solution of a perennial rock-salt crust by rainwater, downward migration of solutions through pores and cracks in the 

crust, and deposition in cavities, most of which 

formed as the result of breaking of the crust during 

uplift because of thermal expansion and contraction. 

FEATURES FORMED BY FAULTING AND 

FRACTURING 

GIANT SALT POLYGONS 

Oriented type.-Aerial photographs of some perennial crusts or thick bodies of rock salt locally show 

polygonal patterns formed by the intersection of two 

or three sets of subparallel lines spaced 200-500 feet 

apart. The lines are thought to be joints along which 

solution and recrystallization of salt has taken place. 

They commonly maintain a consistent orientation 

over areas of a square mile or more. These polygons 

are believed to be indicative of a perennial evaporite 

crust or body that is hard and brittle, and thick 

enough to transmit stresses for long distances. The 

more prominent and consistently oriented polygons 

are believed to be indicative of exceptionally thick 

bodies of salt and of regional stresses associated 

with faulting. The polygons are oriented according 

to the direction of these stresses. 

The best examples of oriented giant polygons are 

in Salar Grande (fig. 31E), where the rock salt is 

several hundred feet thick, and in the northern part 

of Salar de Pedernales (fig. 31G), where the average 

thickness of salt is probably more than 20 feet. 

Similar polygons are faintly visible in aerial photographs of six other salars in northern Chile. Such 

oriented polygons appear to be absent in salars 

having crusts less than 5 or 6 feet thick, even though 

they are in basins showing evidence of recent 

faulting. 

In Salar Grande, the giant oriented polygons are 

best developed near northwest-trending faults that 

displace the salt (fig. 13), and probably are genetically related to these faults. The joints that outline the polygons maintain a fairly consistent 

orientation throughout most of the salar. Near the 

center of the salar the dominant trend is approximately N.35°W., subsidiary trends being roughly 

N.70°W. and N.5°W. 

Giant oriented polygons in the northwestern part 

of Salar de Pedernales extend over an area of at least 

8 square miles. They are probably related to a 

northeast-trending fault believed to pass through 

the northwestern part of this salar. Oil seeps and 

salt pools within the rock salt here may be associated 

with this fault (Harding, 1926, p. 797, 799). Although the fractures that border these polygons are 

clearly visible in aerial photographs, they are obscure on the ground. We were not able to find them 

when we walked over part of this area. The joint 

sets, in order of prominence, trend north, N.80°E., 

and N.40°E., the last set tending to bisect the acute 

(80°) angle between the other two sets (fig. 31G). 

Polygons of a similar type occur in the San Pedro 

Formation, a sequence of evaporites and interbedded 

clastic sediments that has been deformed into a 

series of domal anticlines and has been locally 

faulted. The polygons are visible in photographs of 

the eastern edge of the Llano de Ia Paciencia and of 

the area where it joins Salar de Atacama (fig. 31F, 

P). They are most clearly visible in areas where 

former saline lakes cut relatively smooth terraces 

into the older evaporites. Many of the polygons are 

triangular or rectangular and appear to be bordered 

by parallel joints 100-400 feet apart. Although these 

joints show consistent orientation at a single locality, 

no single regional trend seems to be dominant. 

Randomly oriented type.-High-altitude aerial 

photographs reveal that rock-salt crusts locally have 

giant polygons, commonly 100-300 feet in diameter, 

bounded by randomly oriented fractures. These are 

similar to the small salt polygons that are dominant 

structural features in most salt crusts but that are 

generally too small to be visible in the aerial 

photographs. 

The giant randomly oriented salt polygons appear 

to be best developed in areas of smooth halite flood 

plains, where the rock-salt crust is relatively thick 

and where solution due to periodic flooding is minimal. They were not seen on the ground in Chile but 

are visible in aerial photographs of several salars 

where they appear most clearly as a dark network 

in areas of white salt interpreted to be smooth flood 

plains. Polygons having the same form, but appearing on the photos as a white network on a dark background, occur locally on old perennial rock-salt 

crusts. They are most clearly visible in areas near the 

margins of salt crusts, where a former covering 

layer of silt and sand has been removed by wind or 

where there is occasional flooding. 

The polygons on a white salt flood plain are well 
50 GEOLOGY OF SALARS, NORTHERN CHILE 

developed in the western part of Salar de Talar (fig. 

11, 31H), where the largest are 100 to 300 feet 

across and the smallest discernible on the photos are 

probably about 10 feet across. Polygons of a similar 

type are widespread in the hard halite crust of Salar 

de Coipasa (fig. 8). Polygons in a perennial salt 

crust, showing as a white network on a dark background in aerial photographs, are well developed on 

the north-central part of Salar de Atacama (fig. 

31J), and in the westernmost part of Salar de Pedernales (fig. 311). The most conspicuous polygons 

range from 50 to 100 feet across in the latter locality and 100 to 500 feet across in the former. 

SALT SAG BASINS AND ESCARPMENTS 

Faults cutting Salar Grande (fig. 13) are marked 

by escarpments and by round to elongate depressions 

or sag basins. Escarpments are as much as 5 feet 

high and are rounded because of leaching of salt 

since the last fault movement, which occurred several tens to several hundreds of years ago. Many sag 

basins on the faults are a few feet to several tens of 

feet long and as much as 5-10 feet deep. A few 

larger basins are several hundred feet in diameter 

and 10 feet or more deep. The basins may be due to 

subsurface leaching and collapse along the fault as 

well as to differential fault movement. A prominent 

escarpment and a sag basin occur along a recent 

fault in Salar Grande at the old salt mine, Salina 

Guanillos (fig. 5). This figure also shows a conspicuous basin in foreground that appears to have formed 

largely by surface leaching of the salt. 

SALT PRESSURE RIDGES 

Expansion and contraction of thin salt crusts because of temperature changes cause breaking of the 

crust and may result in formation of polygonal pressure ridges. The breaking and heaving of salt blocks 

is aided by the crystallization of new salt, which 

generally occurs by capillary migration of saline 

ground water, in newly formed fractures and cavities. Pressure ridges are found in two types of salar 

crusts. One type, shown in figure 27, consists of a 

nearly continuous thin layer of rock salt, 1-2 inches 

thick; the ridges result from the buckling of this 

single layer. Such pressure ridges were seen only at 

Salar del Carmen. The other type, a slabby silty 

crust, typical of salars in the Central Valley, has 

ridges 1-4 feet high consisting of upended slabs and 

rubbly fragments (fig. 41). Especially well-developed pressure ridges in this type of crust are in Salar 

FIGURE 41.-Pressure ridges in slabby and nodular silty 

rock-salt crust, which averages about 3 ft in thickness, 

Salar de Bella Vista. 

de Obispo, Salar de Pintados, and Salar de Bella 

Vista. Similar pressure ridges were also seen in the 

northern part of Salar de Punta Negra. 

SALT VEINS 

Salt veins occur in thick rock-salt crusts of salars 

in the Andes of northern Chile and may represent 

an early stage in development of salt polygons in 

such crusts. They also form in cracks within polygons in relatively thin crusts where they are associated with salt cones. They consist of granular salt 

formed along fractures in massive salt in the capillary fringe of the ground-water table. Some veins 

have banding parallel to vein walls. 

White salt veins are widespread in the rugged 

rock-salt crust at the northern end of Salar de Maricunga (fig. 42). They are lj2-2 inches wide and outline polygons that are generally 4-8 feet across. They 

cut across an older set of corroded polygons that are 

2-4 feet across and that are bounded by ridges about 

6 inches high. The rugged salt crust of this area 

borders a halite flood plain and was itself flooded by 

shallow water sometime in the past several years. 

The shallow-water flooding caused both the rugged 

crust to become slightly smoother and the old polygonal cracks to be firmly sealed before formation of 

the new polygons bounded by salt veins. 

FEATURES FORMED BY WIND ACTION 

DUST LOBES 

Salars with extensive soft saline surfaces or granular gypseous crusts commonly trail elongate dust 
FEATURES OF SALAR CRUSTS IN CHILE 51 

FIGURE 42.-Salt veins (white lines) outlining newly formed 

salt polygons in massive rock-salt crust, northwestern 

part of Salar de Maricunga; dark stripes outline old salt 

polygons. 

lobes of windblown material from their leeward 

margins. The lobes consist chiefly of gypsum but also 

contain small amounts of more soluble saline minerals such as halite and thenardite. Large gypseous 

dust lobes extend southeastward from the edge of 

Salar de Pedernales for distances of a mile or more 

(fig. 31Q). The area from which the material in the 

lobes was derived is a gypseous zone which is marked 

by long straight southeast-trending furrows, parallel 

to prevailing wind direction. 

At other places in northern Chile, dust lobes contain a large percentage of clastic sediment derived 

from the salar as well as from bordering areas. 

Such a dust lobe is visible on the western side of 

Salar de Atacama, near its junction with the Llano 

de la Paciencia (fig. 31P). 

Lobes or dunes of sand and salt are found along 

the southwestern margin of Salar de Pintados and 

along the western margin of Salar de Bella Vista. In 

Salar de Pintados, the rugged perennial salt crust 

abuts against a gently sloping piedmont apron which 

is partly covered by prominent dust lobes trending 

northeast (fig. 318). These lobes occur along the 

margin of the salar for more than 5 miles northwest 

of Pintados. The lobes are as much as a mile long 

and a quarter of a mile wide. Each lobe extends leeward from a gully in the adjoining hillside, which 

indicates that the gullies serve to ohannel windblown 

sediment. Some lobes extend out onto the hard salar 

crust for as much as a quarter of a mile. Some of 

these terminate abruptly at the margin of a low area 

in the salar that is subject to infrequent flooding. 

SALT·STABILIZED DUNES 

Sand dunes in the southwestern part of Salar de 

Bella Vista (fig. 13) are now stabilized by a slabby 

silty rock-salt crust that averages 1-2 feet in thickness. The salt crust on the dunes extends over them 

as a continuous layer, which merges with the crust 

of the surrounding flat salar and is identical in appearance (fig. 43A). The salt-stabilized dunes are 

scattered over an area of about 3 square miles, on 

both sides of the Pan-American Highway. They are 

mostly 5-10 feet high and appear as mounds rising 

above the otherwise level plain of the salar. Several 

of the dunes, which are cut by the highway, show 

excellent crossbedding in the sand and a sharp contact with the salar crust (fig. 43B). 

The salt crust on these dunes apparently was deposited by capillary rise and evaporation of ground 

water. However, this took place at a time when the 

water level was higher than its present depth of 1-3 

feet in this area. At the time when the salt crust was 

forming on the dunes, this area may have been sub--

ject to periodic flooding. 

PHREATOPHYTE MOUNDS 

Phreatophyte mounds (Neal, 1965, p. 23) are 

found in several salars and playas of northern Chile. 

They are best developed, however, in the northern 

part of Salar de Pintados where tamarugo trees are 

growing on mounds of windblown fine clastic sediment in an area of thin discontinuous crust (fig. 44). 

These mounds attain heights of as much as 5 feet 

and are 10-20 feet in diameter at their base. Smaller 

phreatophyte mounds are widespread in silt-clay 

playa areas in the eastern part of Salar de Llamara, 

where they have been built up of windblown sediment around low bushes. 

FORMER LAKES IN NORTHERN CHILE 

ANDEAN HIGHLANDS 

Deep lakes formerly occupied parts of many closed 

basins in the Chilean Andes where now only salars 
52 GEOLOGY OF SALARS, NORTHERN CHILE 

B 

FIGURE 43.-Salt-stabilized sand dune, Salar de Bella Vista. 

A, Dune encrusted with platy silty rock-salt layer 1-2 ft 

thick. B, Crossbedded loosely cemented sand in sharp contact with overlying silty rock-salt crust. Notebook is about 

9 in. long. 

and shallow ponds remain. Shorelines and deltas of 

former lakes cut by more recent stream channels 

show clearly on aerial photographs but are less 

clear on the ground. Because detailed topographic 

maps of this region are lacking, it iR difficult to interpret depth of former lakes, degree of tilting of lake 

basins, or changes in drainage divides due to tectonic 

44.-Phreatophyte mound on which tamarugo tree 

(Prosopis tamarugo) is growing in area of thin discontinuous salar crust, northern part of Salar de Pintados. 

The tree is about 12 ft tall. 

movement or uplift during and after drying of 

former lakes. 

Most former lakes in northern Chile and in the 

Andean region of adjoining countries were probably 

of Pleistocene age, but some may have existed during 

late Pliocene and others during Holocene time. For 

example, recent investigations of the paleontology 

and stratigraphy of lake sediments in the basin of 

Salar del Guasco indicate they are of Pleistocene age 

(Jaime Sayes, written commun., 1968). 

Surprisingly little has been written about former 

lakes in northern Chile, considering their number, 

size, and, in some cases, great depth. These have 

been discussed by Bowman (1924), Ogilvie (1922), 

Briiggen (1950), Wurm (1940), Vita-Finzi (1959), 

and a few others. 

During the present investigation, only a few of the 

basins containing relatively deep former lakes were 

visited. However, the aerial photographs show clear 

evidence that moderately deep perennial lakes formerly occupied parts of at least 35 of the 67 closed 

basins in the Andean Highlands of northern Chile. 

Most of these lakes are indicated in figures 8-12. 

However, in several basins, for example that of 

Salar de la Isla (fig. 12), the shorelines of the former 

lake are so close to the margin of the present salar 

that they could not be shown on the map. The lakes 

in such basins may have been large and deep, as 
FORMER LAKES IN NORTHERN CHILE 53 

was the lake that formerly occupied the basin of 

Salar de Ia Isla. The principal former lakes, shown 

in the above-mentioned illustrations, and their estimated maximum sizes are listed in table 3. 

TABLE 3.-Location and size of the principal former lakes 

in northern Chile 

Present salar or lake in basin (numbers Approximate size of former 

refer to localities shown in figures 8-12) lake in basin (sq. mi) 

Salar de Surire (2) --------------Unknown (incomplete photocoverage) . 

Unknown name (4) ---------------29 

Salar de Coipasa (5) ------------Unknown (largely outside Chile) • Salar del Guaseo (11) -------------67 

Salar de Coposa (12) -------------98 

Salar de Ollagiie (14) ------------Unknown (largely outside Chile). 

Salar de San Martin (15) ---------68 

Salar de Ascotan (16) ------------104 

Salar de Talar (28) --------------12 

Salar de Aguas Calientes1 and 

Purisunchi (29) ----------------40 

Laguna Tuyajto (30) -------------7 

Salar de Aguas Calientes 1 (31) ---56 

Laguna Miscanti (31E) -----------11 

Salar de Pujsa (32) ---------------31 

Salar de Aguas Calientes 1 (33) ----14 

Salar de Laco (34) --------------- 9 

Salar de Quisquiro (35) -----------67 

Salar de Tara (36) ---------------78 

Pampa de Tara (37) --------------7 

Unknown name (43) -------------4 

Salar de Pular (44) --------------21 

Salar de Incaguasi (45) ----------85 

Salar de Aguilar (49) -------------47 

Salar de Agua Amarga (51) ------11 

Salar de Pajonales (52) ----------- 66( ?) 

Salar Grande 1 (54) ---------------13 

Salar de Gorbea (55) -------------16 

Laguna de la Azufrera (58) _______ 7 

Salar de las Parinas (59) ----------10 S·alar de Pedernales (60) __________ 210 

Salar de Maricunga (61) -----------56(?) Salar de Piedra Parada (65) ______ 18 

Salar Wheelwright (67) __________ 3 

Lagunas Bravas (68) _____________ 7 

Laguna Escondida (71) ___________ 13 

Laguna Verde (72) _______________ 20 

J,agouna del Negro Francisco (74) __ 30 

Unknown name (76) ------------7 

1 Three salars in northern Chile are named Aguas Calientes. 2 Two salars in northern Chile are named Salar Grande. 

SHORELINES 

Shorelines of former lakes appear in aerial photographs of many closed basins now containing a salar 

or a lake in the Andes of northern Chile, indicating 

more extensive flooding in the past. The shorelines 

appear to be best preserved where they are well 

above the present water level or salar margin and 

where the former lakeshores were fairly steep. 

Stream channels approaching many salars are 

graded to a level near that of the highest clearly 

recognizable shoreline, being less well defined below 

this level than above, thus indicating former larger 

streams. Some streams that now are deepening channels above the highest shoreline of a former lake 

apparently have little or no effect on channels below 

this shoreline because here the stream sinks into the 

highly permeable lake sediments. Such is the case at 

Salar de Aguas Calientes (fig. 11, no. 33), where 

channels with flowing streams end at the uppermost 

shoreline, the lower shorelines being virtually 

undissected. 

Exceptionally well preserved shorelines can be 

seen in aerial photographs of the following Andean 

basins (figs. 9, 11, 12) : Salar del Guasco, Salar de 

Coposa, Salar de San Martin, Salar de Tara, Salar 

de Puj sa, Salar de Aguas Calientes, Salar de Quisquiro, Pampa de Tara, and Laguna del Negro Francisco. The most detailed and extensive shorelines in 

all of northern Chile are in the basin of Salar de 

Tara (fig. 31U) where at least 24 terraces are recognizable around the eastern end of the salar. Their 

formation and preservation appear to be favored by 

the relatively soft porous material, probably tuffaceous sediments, in which they occur. The inft.uence 

of prevailing westerly to northwesterly winds is indicated by the development of the most prominent 

shorelines in the eastern and southeastern parts of 

the above basins. Of the 27 most prominent shoreline areas that can be seen in aerial photographs, 11 

are southeast and 9 east of the present salars. 

Around the margins of many salars, particularly 

those at lower elevations in the Andes, the evidence 

of former lakeshores generally is obscure. Faint 

lineations around some salars seem to be the shorelines of very shallow or intermittent lakes. Shorelines in basins tilted by tectonic movement may aPpear to have the form of low terraces or steps 

crossed by many shallow channels flowing toward 

the lower parts of the basin. Such shorelines, which 

are apparently undergoing destruction, can be seen 

at the northern and eastern margins of Salar de 

Aguas Calientes (fig. 11, no. 31), the southwestem 

margin of Salar de Quisquiro (fig. 11), and the 

northwestern margin of Salar de Ia Isla (fig. 12). 

The highest clearly recognizable shorelines at the 

southeastern side of Salar de San Martin (fig. 9) 

and at the western side of Salar de Ollagiie are between 12,400 and 12,500 feet and indicate the presence of a large former lake in these basins. This lake 
54 GEOLOGY OF SALARS, NORTHERN CHILE 

undoubtedly was connected with the former Lago 

Minchin, which covered much of west-central 

Bolivia, including the basins of Salar de Uyuni, Salar 

deCoipasa, Salar de Empexa, and Salar de Chiguana 

(fig. 1). The highest shorelines of Lago Minchin, 

measured far to the north in Bolivia, are reported 

to be at about 12,500 feet (Ogilvie, 1922, p. 42-44). 

At its greatest extent this lake was about 300 miles 

long, nearly connecting with Lake Titicaca at the 

Bolivia-Peru border, and had a maximum depth of 

more than 400 feet. It covered an estimated 10,000 

square miles, an area roughly the same as Lake Erie 

in the United States. 

Several altimeter measurements give an indication 

of the depth of the former lake in Chile and its relation to the divide between Salar de San Martin and 

Salar de Ascotan. Prominent beaches indicate a 

maximum depth of about 250 feet in the basin of 

Salar de San Martin and about 220 feet in that of 

Ollagiie. The lowest part of the pass between Salar 

de San Martin and Salar de Ascotan is about 12,680 

feet, 260 feet above the nearby . highest shorelines. 

Because of the height of this pass, it appears that 

lakes in these two basins were not interconnected at 

the time that Lago Minchin existed. 

DELTAS 

Prominent deltas, best seen in aerial photographs, 

are at the margins of several salars. Many of these 

deltas, including those at Salar de Tara (fig. 11), 

Salar del Guasco and Salar de Coposa (both in fig. 

9), have well developed lakeshores at their upper 

edges, indicating that at the highest levels of former 

lakes the deltas were largely under water. As lake 

levels receded, the deltas were reworked, and lower 

shorelines form·ed. Some were dissected by streams, 

as can be clearly seen in aerial photos of Salar de 

Tara and Salar de Ollagiie. Stream dissection is generally greatest in the upper parts of the deltas where 

the stream channels commonly cut across steepsided terraces. The lower parts show much less dissection, and in some cases none. Most of the present 

stream flow is commonly lost by seepage into the permeable deltaic sediments, reappearing again as 

springs along the margins of the salars. 

Salar del Guasco (fig. 15) is the remnant of a 

much larger lake that left well-preserved shorelines, 

including prominent lake terraces, particularly 

northeast and southeast of the salar, and a large 

delta to the north. One prominent terrace at the 

eastern side of the salar was measured to be 100 

feet above the salar. Briiggen (1929, p. 5) reported 

a terrace at that level. Still higher terraces, which 

we did not measure, are estimated to be at least 150 

feet above the present salar. An extensive gently 

sloping plain extending for more than 5 miles north 

of the salar is interpreted as a delta. The highest 

shorelines are at the margins and above this delta, 

indicating that the delta was under water at the 

highest lake level. The delta is dissected by present 

stream channels, which are most prominent in its 

upper parts. 

A decrease in streamflow that accompanied lowering of lake levels is well shown by a series of deltas 

on the east side of Laguna de Tuyajto (fig. 31 V). 

The oldest delta was apparently below water at the 

highest former lake level. Successive lake shorelines 

are recorded by a series of terraces that are truncated by the delta plain, indicating that the delta 

continued to receive sediments while the lake receded. At a very low lake level, not far above the 

present salar, deposition on the emerged delta stopped, streamflow was confined to one or two steepsided channels, and the lower edge of the delta was 

largely truncated at this lakeshore. During the final 

stage of :lake desiccation, a small subsidiary delta 

(fig. 31) was apparently built out into the lake by 

a small stream. This small delta has now emerged 

and is inactive, but is crossed by a small intermittent stream which has built a new alluvial fan, 

approximately 300 feet wide, at the margin of the 

salar. The decrease in area of these successive deltas 

or fans gives a very rough indication of the decrease 

in runoff and of alluvial sediment that reached the 

lower part of the basin. The delta covered more than 

600 acres at highest lake level but only about 40 

acres at a very low lake level. The alluvial fan currently being formed is less than an acre in extent. 

The northeast side of Salar de Tara (fig. 11) and 

westernmost end of Salar de Ollagiie (fig. 9) show a 

spectacular record of development of deltas and 

shorelines. The delta in Salar de Ollagiie is unique in 

having at its toe a series of cuspate spits that evidently formed in the shallow waters of the lake 

during its last stage of desiccation. 

DRAINAGE CHANGES DURING HIGH LAKE LEVELS 

From features seen in aerial photographs, several 

former lakes in the Andean Highlands appear to 

have overflowed their divides into adjoining basins. 

This is well illustrated by Salar de Aguas Calientes 

(fig. 11, no. 33), where the highest former lakeshore 

at the southeast side of the salar is cut by a ·Steepsided stream channel (fig. 31T) that connects south-
FORMER LAKES IN NORTHERN CHILE 55 

eastward with the basin of Salar de Quisquiro. Other 

drainage changes that appear to have occurred when 

lakes were at high levels are as follows: 

1. A lake in the basin of Salar de Coposa (fig. 9) 

overflowed northward into a lake in the basin 

of Salar de Empexa. 

2. A lake in the basin of Salar de San Martin (fig. 

9) coalesced with one in the basin of Salar de 

Ollagiie, forming an arm of former Lago 

Minchin. 

3. The lake in the basin of Salar de Tara (fig. 11) 

overflowed into one in the basin of Salar de 

Aguas Calientes. A lake in Pampa de Tara 

(fig. 11) appears to have coalesced with that 

in the basin of Salar de Tara. 

4. A.lake in the basin of Salar de Pujsa (fig. 11) 

apparently extended westward, joining a small 

lake at the salar that is about 4 miles to the 

west. 

5. A lake at Laguna de Tuyajto (fig. 11), when at 

its highest level, probably overflowed into the 

basin of Salar de Incaguasi. 

6. The basins of Salar de Talar and Salar de Purisunchi (fig. 11) were apparently formerly occupied by an interconnected lake. 

LACUSTRINE SEDIMENTS 

The lacustrine sediments in closed basins of the 

Andean Highlands of northern Chile consist of sand, 

silt, and clay, largely of volcanic origin, and locally 

of reworked volcanic ash. Diatomaceous earth layers 

have been found at several localities, and such layers 

may be widespread in lake sediments of the area. 

The sediments of a few of the Andean basins, described below, give an idea of the general character 

of the lacustrine sediments throughout the northern 

Chilean Andes. 

Lake sediments in the basin of Salar del Guasco 

(fig. 15) consist of interstratified clay, silt, and diatomaceous earth layers having a probable maximum 

thickness of several hundred feet. A diatomite layer 

was sampled in a shallow cut (fig. 45) near the 

northwest side and 30--40 feet vertically above the 

present salar. The diatomite was estimated to consist of about 75 percent diatoms. At a late stage of 

desiccation of the former lake, large amounts of 

pyroclastic debris, including abundant pumice fragments, were deposited. A low terrace at the northern 

side of the salar, 5-10 feet above the present salar 

level, contains rounded pebbles of pumice, apparently 

washed up on the shore of the former lake. 

FIGURE 45.-Diatomite layer deposited in a former lake, 

northwestern side of Salar del Guasco. 

Salar de Coposa is in a basin that was once occupied by a large lake, as evidenced by well-preserved 

lake sediments and terraces at high levels around its 

margin, and by a large delta at the northeast side 

that is dissected by present streams (fig. 15). Two or 

more terraces presumed to be lake terraces are present along the western and southern sides of the salar, 

the highest prominent terrace being approximately 

75 feet above present salar level. Terraces are most 

prominent along the eastern side, but on both sides 

they seem to be blanketed by volcanic material and 

possibly mudflows, which have obscured their outlines and particularly their upper limits. A valley 

south of the salar, Quebrada del Pabell6n (not shown 

in fig. 9), appears to be occupied by lake sediments 

(Gabriel Perez, written commun., 1967) that extend 

nearly 9 miles to the south. Sediment from an area 

about 1.3 miles south of the salar was found to contain diatoms and to have small vertical tubes, evidently formed by roots of plants that grew in the 

shallow margins of a former lake. 

The lake sediments have been blanketed by volcanic ash at several places around Salar de Coposa, 

the ash being deposited when the former lake had 

almost disappeared. The ash is thickest east of the 

salar; the volcanic source was probably in this direction. At the west side of the salar the lakebeds are 

overlain by a unit of white relatively undisturbed 

ash or pumiceous tuff, above which is a unit of reworked pyroclastic material. The upper unit appears 

to have been washed over the surface possibly as a 

mudflow, shortly after deposition of the . underlying 

unit. Both units are variable in thickness and con-
56 GEOLOGY OF SALARS, NORTHERN CHILE 

form roughly to the slope of the present land surface. They have a total thickness of more than 20 

feet. 

The extensive tuffaceous deposits at the southeast 

side of Salar de Coposa (fig. 15) consist of loose to 

compact, light-gray, pink, and white pyroclastic material, including considerable pumice. The maximum 

exposed thickness is about 20 feet, but it is estimated 

that the tuff is generally many tens of feet thick and 

that it may attain a maximum local thickness of 

several hundreds of feet. Layering of the tuff is more 

or less parallel to present ground surface which is 

inclined gently to the west. 

A special study was made of samples of beach 

deposits in the basins of Salar de Ollagtie and Salar 

de San Martin (Samples 20 and 37, table 2), to get 

an idea of the character of such deposits in the 

Andean Highlands. The samples were taken from 

about 10 feet below the highest prominent shorelines 

in both basins, at elevations between 12,400 and 

12,420 feet. 

The samples are similar in composition, consisting of about 94 percent sand and gravel and about 6 

percent silt, and constitute a poorly graded silty sand 

(soil type SP-SM}. Clastic grai-ns in both samples 

are coated with calcium carbonate deposited after 

beach formation. Grains are predominantly subrounded in both samples ; those larger than one 

eighth of an inch in diameter from the beach at Salar 

de Ollagtie are slightly more rounded, being classed 

as subrounded to rounded. The size gradation of the 

samples is comparable, average frequency distribution being shown on figure 16. The sediments are 

similar to mixtures of beach sand and gravel found 

on beaches elsewhere. 

Near the settlement of Ollagiie (fig. 1), a beach 

terrace near the level of Salar de Ollagiie is covered 

with calcareous tufa. The terrace is well developed 

northwest of Ollagiie, and in aerial photographs it 

appears to form a broad plain extending for several 

miles northeast of that settlement. The tufa apparently was deposited in shallow water at the edge of 

a former lake. It includes abundant ostracodes that 

are incorporated in and partly encrusted by the concentrically banded calcareous tufa that may have 

been deposited by algae. Further desiccation of the 

lake initiated deposition of gypsum which predominates in the salar crust near Ollagiie. 

ATACAMA BASIN AND VICINITY 

The Atacama basin and nearby basins to the west 

and south along the east side of Cordillera Domeyko 

(figs. 10 and 11) differ from the basins in the Andean Highlands in lacking high shorelines and large 

deltas indicative of large former lakes. One might 

conclude that the lakes in these basins were not materially larger than the present salars, even when the 

largest lakes existed in the Andean Highlands. On 

the other hand, diatomaceous earth deposits in the 

Atacama basin seem to indicate that a former large 

lake extended 10 kilometers or more east of the present salar. Conversely, these deposits may have 

formed in a small lake, perhaps one of several that 

once existed in the Atacama basin. The diatomite 

deposits are nearly 1,000 feet above the level of the 

present salar and dip nearly 5°W., indicating sinking of the basin and tilting westward. Parameters 

of a former large lake that probably existed in the 

Atacama basin are listed in table 4. 

TABLE 4.--C~parisan of probable former lakes in the Atacama Basin and in the Central Valley (Gran Lago Soledad) 

Gran Lago 

Soledad Atacama Basin 

Drainage-basin area __ 12,870 sq mi 

(Rfo Loa 

4,530 sq mi ( Salar 

de Atacama 

only-) only) 

Maximum probable 19,150 sq mi 5,260 sq mi 

drainage area, ineluding adjoining basin. 

Former lake area 770 sq mi(?) 1,300 sq mi ( ?) 

(estimated). ( excl. Salar 

Grande) 

Maximum depth of 250 ft(?) 20 ft( ?) 

former lake 

(estimated). 

Mean depth of former 100 ft( ?) 15 ft(?) 

lake (estimated). 

Volume of former 15 cu mi(?) 4 cu mi(?) 

lake (gross 

estimate). 

Elevation of former 2,720 ft 7,500 ft 

lake ( approx.). 

Mean elevation of 7,750 ft 10,750 ft 

drainage basin. (weighted (estimated) 

by percent of area) 

Mean elevation of 9,800 ft 13,900 ft 

divides. 

Mean annual precipi- 2 in. 2 in. 

tation in basin 

(estimated). 

Ratio: Drainage area/ 1.3 (approx.) 1.3 (approx.) 

volume of lake. 

The only shorelines and lake terraces evident in 

the aerial photographs of the Atacama basin are 

along the east side of the Llano de la Paciencia and 

at the north end of an anticlinal dome bordering a 

low pass in the Cordillera de la Sal (fig. 31P). A 

lake in the Llano de la Paciencia once was connected 

to the main lake in the Atacama basin to the east, 
ENVIRONMENT OF PRESENT AND FORMER LAKES 57 

through this pass. The lake terraces are cut in the 

soft saline sediments· and interbedded rock salt of 

the San Pedro Formation. Three distinct broad 

wave-cut terraces can be seen in the photographs. 

These terraces are 5-30 feet above present salar 

level. Less distinct terraces can be seen at higher 

levels, perhaps an additional 25-50 feet above the 

more distinct lower terraces. 

CENTRAL VALLEY AND COASTAL RANGE 

The Central Valley of southern Tarapaca Province 

and northern Antofagasta Province (fig. 1) once was 

occupied by a large lake known as Gran Lago Soledad (Briiggen, 1950, p. 151-152). This lake may 

have overflowed periodically into the basin of Salar 

Grande. Extensive deposits of gypsum and anhydrite 

in and around Salar de Llamara are attributed to 

this lake, as is the solid body of rock salt in Salar 

Grande. Extensive halite crusts and anhydrite-gypsum crusts elsewhere in this part of the Central Valley also are attributed to this lake. Estimated parameters of this former lake are shown in table 4. 

At its highest level, Gran Lago Soledad apparently 

attained a depth as great as 250 feet, as indicated by 

shorelines on Cerro Soledad, an isolated ridge in the 

eastern part of the salar, and in the low pass between 

Salar Grande and Salar de Llamara (fig. 9) . The 

highest former lake shorelines do not appear to be 

level at present, possibly the result of tilting due to 

tectonic movement. For example, the highest apparent shoreline in the pass near Salar Grande is 

estimated to be at an elevation of 2, 720 feet, whereas 

a shoreline that appears comparable along the northernmost edge of Salar de Llamara is estimated to be 

about 100 feet higher, and farther north appears to 

rise to nearly 2,900 feet. At a high level the lake 

appears to have overflowed a divide in the Coastal 

Range, initiating the downcutting of the Rio Loa 

(fig. 9), and subsequently cutting a steep-sided gorge 

several hundred feet deep. 

Elsewhere in the Central Valley and Coastal 

Range, the presence of former lakes is indicated 

only by lake sediments. Shorelines and deltas, well 

shown in basins of the Andean Highlands, are absent. Consequently, our knowledge of size and distribution of the lakes is scanty; we do not know their 

relative ages, nor can we relate them to the period of 

lake development in the Andes. 

Lacustrine sediments are widespread in the Pampa del Tamarugal (fig. 1), locally attaining thicknesses of 200 feet or more. These sediments are well 

exposed along the Rio Loa in northern Antofagasta 

'Yhere they consist of interbedded fine-grained clastic sediments, limestone, diatomaceous earth, and 

evaporites. Salar del Miraje, in the Pampa del Tamarugal in the vicinity of Oficinas Maria Elena and 

Pedro de Valdivia (fig. 1), is covered with dissected 

lake sediments, apparently the upper part of the sequence exposed by the Rio Loa. The sediments consist of interbedded silt and sand layers, some of 

which are firmly cemented with halite, anhydrite, 

or gypsum. Locally, the surface is covered by a dry 

friable soil consisting of clastic sediments and powdery gypsum or anhydrite. Still farther south, in 

the region near Aguas Blancas (fig. 1), widespread 

clastic lake sediments and interbedded anhydrite 

occur in an elongate closed basin that is a segment of 

the Central Valley. These sediments may attain 

thicknesses of several hundred feet. 

Soft diatomaceous earth has been found as a surface layer or a layer just below thin salar crusts at 

several places in the Pampa del Tamarugal, indicating the presence of lakes during late Pleistocene or 

even Holocene time. 

ENVIRONMENT OF PRESENT AND 

FORMER LAKFS 

It has been found that the relative sizes of former 

lakes in northern Chile, as indicated by basin/lake 

ratios, do not show a simple relationship to gross 

environmental factors such as mean annual precipitation, basin elevation, basin slope, or rate of evaporation. It is concluded that sizes of the former lakes 

were controlled by factors such as topography, hydrology, and geology, as well as by the above-mentioned gross environmental factors. Furthermore, 

the existence of lakes in certain basins and their 

absence in others cannot be correlated with present 

gross environmental factors. The following tabulation in which the basins showing clear evidence of 

former lakes are compared as a group with all the 

basins in the northern Chilean Andes, shows no significant differences between the two groups in elevations of basins, elevations of divides, mean annual 

precipitation, mean annual temperature, and index 

of potential evaporation. 

Only five of the closed basins in the Andes of 

northern Chile have relatively large perennial lakes 

rather than s.alars. However, many of the salars of 

this region have small perennial ponds. These lakes 

and ponds provide a means of estimating gross environmental factors that favor their development 
58 GEOLOGY OF SALARS, NORTHERN CHILE 

Groupe of basins 

All 84 drainage 

basins in the 

Andean Highlands, and in 

the Atacama 

Basin and 

vicinity. 44 drainage 

basins having 

good evidence 

of former 

lakes. 

Present gross 

topographic condition 

Present gross 

climatic conditions 

Mean 

annual 

precipitaMean Mean tion 

basin elevation (inches, 

elevations of divides esti-

(in feet) (in feet) matecl) 

13,450 14,700 7.3 

13,400 14,300 6.7 

Mean 

Mean index of 

tempera- evapom- ture ( F, tion 

esti- (estimated) mated) 

39 24 

39 25 

and of estimating the climatic changes required to 

produce the more numerous and larger former lakes. 

EXISTING LAKES 

Basins in which perennial lakes rather than salars 

now are present are Laguna Miscanti, Laguna 

Wheelright, a small lake southeast of Lagunas 

Bra vas, Laguna Verde, and Laguna del Negro Francisco (figs. 11, 12). A comparison of these five basins 

with 95 other closed basins in northern Chile shows 

that the five basins containing lakes have four of the 

22 highest values of mean basin elevation (the fifth 

basin ranks thirty -third) , five of the 29 highest 

values of mean annual precipitation (estimated), 

and five of the 14 lowest values of potential evaporation index (estimated). 

Of the five basins with lakes, four are among the 

six basins in which all of the four critical values, 

listed below, are high. These values for the group of 

100 basins in northern Chile are as follows: 

1. Mean elevation of basin, 15,000 feet or more 

(22 basins). 

2. Mean elevation of divides, more than 16,500 

feet (9 basins). 

3. Mean annual precipitation, 9 inches or more 

( 29 basins) . 

4. Index of potential evaporation, 16 or less (14 

basins). 

Of all the basins, only 14 meet or exceed two of these 

critical values, and only six basins meet or exceed 

all four conditions. As the six basins having all four 

conditions include four out of five basins presently 

containing lakes, the four stated conditions might be 

considered the most critical values favorable for 

lake formation in northern Chile. Other factors may 

influence lake formation, but our information is too 

scanty to allow us to evaluate them. 

The gross environmental factors favoring formation of perennial lakes in northern Chile are summarized in a circle graph (fig. 46). The graph shows 

that six to eight additional basins probably have 

conditions presently favorable for lakes. The absence 

of lakes in some of these basins is probably due to 

subsurface leakage of the basin, and in others to 

factors not yet recognized. 

The basin of Laguna Verde (fig. 12) typifies the 

conditions favorable for perennial lakes in northern 

Chile. The mean elevation of the basin is approximately 16,000 feet; the lake itself is near 14,500 

feet. The basin is rimmed by exceptionally high divides having a mean elevation of about 17,400 feet. 

The rim of the basin includes at least five peaks more 

than 19,500 feet high. The highest peak, Ojos del 

Salado, is reported to attain an elevation of about 

22,580 feet, shown erroneously on a recent map 

(ONC) as 23,240 feet. The few peaks that rise above 

21,000 feet have perennial snowfields, and Ojos del 

Salado is reportedly one of only three peaks in Chile 

north of lat. 30°S. having small glaciers (Lliboutry 

and others, 1958). Mean annual precipitation in the 

basin is estimated to be approximately 13 inches, and 

the index of potential evaporation would be about 12, 

probably the lowest of all the basins. 

FORMER LAKES 

Environmental factors favoring present-day lake 

formation in northern Chile give a clue to the past 

environment when perennial lakes were more numerous. The required increases in mean annual precipitation or decreases in mean annual temperature 

for different regions are shown in figure 4 7. The 

equivalent amounts of change of these two factors 

are based on their estimated relation to the potential 

rate of evaporation. These relations have been investigated by Langbein (1961) as an aid in estimating hydrologic regimes in areas of little meteorological data, the relative effect of precipitation and 

temperature varying in different climates. 

The estimated changes in climate required to produce perennial lakes in each of the three major subregions containing salars are as follows : A very 

small to moderate increase in precipitation, or 

equivalent decrease in temperature, would favor the 

reestablishment of the former perennial lakes in the 

Andean Highlands. Large changes in one or both 

factors would favor perennial lakes in the Atacama 
8 

ENVIRONMENT OF PRESENT AND FORMER LAKES 

Cl;matk !acton/ 

EXPLANATION 

(Numbers refer to basins shown in figs. 8 to 12 and tables 1, 3) 

Drainage basin containing perennial 010 intermittent lake occupying predominant part of flat basin floor 

Drainage basin containing no lake or very small lake, and showing little or no evidence of former lake 

Drainage basin showing substantial evidence of former lake and large salars, but in which lakes are 

now either absent or subordinate to solar crusts 

FIGURE 46.-Topographic and climatic factors favoring occurrence of perennial lakes in closed drainage 

basins of northern Chile. 

59 
60 GEOLOGY OF SALARS, NORTHERN CHILE 

0 so 100 200 300 

MILES 

KILOMETERS 

BOLIVIA 

Required increase in mean Required decrease in mean 

Number annual precipitation only annual temperature only Region 

(in.) ("f) 

Region presently favorable for lakes in Andean Highlands 

1 None None south of lat 26°30'5.; also small regions in eastern Antofagasta Province 

2 1-2 2-3° Andean Highlands, chiefly in east-central part of Antofagasta 

Province 

3 .._s s-r Andean Highlands, chiefly in northeastern part of Atacoma 

Province 

.. S-7 7-9° Crest of Andean Highlands between lat. 24°5. and 

25°30'5. 

5 9-11 12-l4° Andean Highlands east of lquique between lat 2005. and 2r5. 

6 11-15 16-18° Western ranges of the Andean Highlands between lat 25°5. 

and 2rs. 

Atacoma Basin and vicinity; also adjoining basins in lower 

7 Over 20 Over 20° parts of the Andean Highlands in eastern Antofagasta 

Province 

8 Large increase Large decrease Rio Loa drainage basin; probably a former closed basin drain· 

ing inta Solar de Llamara 

9 Extraordinarily large Extraordinarily large Closed drainage basins of salars in Coast Range and Central 

inaease decrease Valley, lat 19°5. to 250S. 

FIGURE 47.-Estimated climatic changes necessary to produce lakes in closed drainage basins in 

northern Chile. 
ENVIRONMENT OF PRESENT AND FORMER LAKES 61 

Basin and vicinity, as well as in the Rio Loa basin. 

Extraordinarily large changes in one or both factors 

appear to be required in the remainder of the Central 

Valley and Coastal Range areas. 

Very little has been published about glacial deposits in northern Chile. Moraines have been described 

near the eastern edge of the Rio Loa drainage basin 

(Briiggen, 1950; Hollingworth and Guest, 1967). 

No glacial deposits were observed on aerial photographs or in the field during the present study. The 

general lack of glacial deposits, cirques, or other evidences of glaciation, even at elevations of 15,000 

feet and above in the Andean Highlands, suggests 

that the climate during glacial stages of the Pleistocene was not much different from that of today. 

Inasmuch as deep perennial lakes have left their 

evidence in at least half the basins in the Andean 

Highlands, the lakes being widely distributed 

throughout the region, there is little doubt that the 

climate of this region was formerly somewhat more 

humid. A circle graph (fig. 48) similar to figure 46 

has been prepared to show the estimated effects of a 

small to moderate increase in precipitation on probability of lake formation. This graph is based on an 

estimate of climatic conditions that would be favorable for simultaneous formation of perennial lakes in 

nearly every topographically closed basin in the 

northern Chilean Andes whose hydrologic closure is 

sufficient to hold water. It is estimated that these 

climatic conditions are reflected by the hypothetical 

curve of elevation vs. precipitation 2 shown in the 

lower left corner of figure 48. This graph shows that 

at all elevations the hypothetical precipitation would 

need to be about twice that which now falls in the 

region, although at elevations below 10,000 feet the 

increase would need to be less than 2 inches annually. 

Above 10,000 feet, the hypothetical increase in precipitation required to produce a pluvial age is estimated to be equivalent to present precipitation at 

s The hypothetica.l elevation versus precipitation eurve in figure 48 

was constructed as follows: ( 1) the driest part of the Andean Highlands 

in which lakes formerly occurred (region no. 6, fig. 47) was compared 

with the more humid adjoining parts in which lakes now oeeur; (2) 

the amount of increased precipitation and decreased temperature necessary to produce conditions in region 6 similar to those now found in 

region 1 was estimated; (3) an arbitrary overall decrease in mean 

annual temperature of 2° F. was assumed, and the required change in 

rainfall was estimated from the curve of precipitation vs. elevation based 

on present climatic conditions; ( 4) it was assumed that the former 

mean annual precipitation was constant throughout the Andean Highlands at given elevations and that the elevations of drainage basins were 

the same as at present. 

Because of normal fluctuations in climate, both in space and time, 

the curve in figure 48 is intended as a rough estimate of the character 

of former climates likely to have been associated with Jake formation 

during some exceptionally humid period in specific regions subregions 

or even in specific lake basins, and not necessarily the Iong:term clima~ of the region as a whole. 

elevations no more than 2,000-2,500 feet higher. 

When one collBiders the great relief of the Chilean 

Andes, in which at least 60 closed basins have divides averaging over 14,000 feet in elevation, this 

required increase in humidity does not seem extraordinarily large. The estimated average increase in 

annual precipitation required for such a pluvial age 

ranges from about 5 inches at 12,000 feet to 10 

inches at 15,000 feet. 

Although a uniform decrease in mean annual temperature of 2°F was arbitrarily assumed for all 

basins in northern Chile, to permit preparation of 

figure 48, a larger temperature decrease would favor 

lake formation with less change in precipitation. On 

the average, each additional decrease of 2°F in 

mean annual temperature was estimated to be roughly equivalent to an increase of 1 inch in mean annual 

precipitation. It is concluded that if the above hypothetical climatic conditions persisted for several 

years over northern Chile, perennial lakes would 

tend to form in basins having mean elevations approximately 2,000 feet lower, or drainage divides 

roughly 2,500 feet lower, than the basins in which 

perennial lakes now occur in northern Chile. 

During such a hypothetical climate, perennial lake 

formation would be favored in the following basins: 

those having mean elevations of drainage divides 

higher than 14,000 feet; those whose mean overall 

elevations were higher than 13,000 feet; those receiving 15 or more inches of annual precipitation 

averaged over the basin; and those in which the 

potential rate of evaporation was an index of 16 or 

less. When all the 100 principal closed basins in 

northern Chile are considered in terms of these 

factors, 58 basins in the Andean Highlands (those 

clustered in the center of fig. 48) would be highly 

favorable for lake formation and three more would 

be moderately favorable during such a period of 

more humid climate. These 61 basins constitute 90 

percent of the 67 closed basins in the northern 

Chilean Andes. 

The hypothetical former precipitation pattern indicated in figure 48 would probably be insufficient to 

produce perennial lakes in the Atacama Basin and 

vicinity, although it undoubtedly would result in 

higher ground-water tables and the formation of 

lakes in some of these lower basins. A somewhat 

higher regional precipitation or lower temperature 

would be required to form numerous perennial lakes 

in this lower region. Nevertheless, it seems evident 

that a climate sufficiently humid to produce extensive 

perennial lakes in most of the Andean basins would 
62 GEOLOGY OF SALARS, NORTHERN CHILE· 

16 

15 

;u 

• -13 

0 

Ill 12 ~ 

~11 Ill 

~ 10 

-:£ 

9 c:: 

! 8 a 

_! 7 

w 6 

5 

.4 

Precipitation-elevatiOft !l'aph 

I 

---v -~ ... "' ~ 

- I .,.""" - 1/ / 

/ 

I I 

I I 

// 

,, 

~I 

t 

0 2 4 6 8 10 12 14 16 18 20 

Mean annual precipitation (in.) 

Solid curve is present average for all 

basins; dashed curve is hypothetical 

(see text) 

NOTE: 

/

Existing 

topographic 

factor 

Hypothetical 

climatic fcn:tor 

Closed drainage basins satsifying one or more of the four critical 

factors, indicated by the large circles, are shown by small numbered 

circles. Numbers refer to basins shown in figures 8-12. All the 

closed basins in northern Chile have been considered; the 61 basins 

shown here are within the Andean Highlands. 

FIGURE 48.-Topographic and climatic factors that would have favored formation of perennial lakes in closed basins 

in the Andean Highlands of northern Chile. 
CONCLUSIONS 63 

strongly favor the occasional formation of perennial 

lakes in most of the bordering basins to the west. 

At the time of high lake levels in the Andean Highlands, perennial lakes may have formed in basins in 

the Central Valley that are supplied by Andean 

drainage. The basin of Rio Loa is particularly well 

situated to receive runoff from the high Andes. It 

can be shown that flooding in the Atacama Basin, 

unless of a very local nature, would probably also 

have been accompanied by flooding of Salar de Llamara, prior to its ·dissection by the Rio Loa, and 

that the same climate required to produce a lake 

20 feet deep in the Atacama Basin could produce a 

lake 250 feet deep in the Rio Loa basin. In our study 

we believe there is good evidence that former lakes 

attained at least these depths in the two basins. 

The climate, at least in some of the less arid 

basins, appears to have been slightly drier at some 

former time. For example, Laguna del Negro Francisco (fig. 12) appears once to have been shallower. 

A prominent island within the lake, about 2 miles 

long and 100-1,000 feet wide, is apparently covered 

by shorelines, some extending below present water 

level. The shorelines extend across the lake floor, 

being visible beneath the shallow water. Evidently 

the lake formerly occupied only the northwestern 

part of its present area and maintained that size long 

enough to build fairly prominent shorelines. 

CONCLUSIONS 

Our purpose was to study the total environment 

of existing salar crusts in the Atacama Desert and 

Andean Highlands of northern Chile to gain a better 

understanding of processes that modify them and to 

help interpret past climates of the region. Salars 

offer an unusually good opportunity for such a study 

because they receive the drainage from large closed 

basins and are responsive to a wide range of environmental factors, including geology, hydrology, 

topography, and climate. 

The study was aided by excellent aerial-photograph coverage of all of northern Chile, which permitted photointerpretation of 75 salars and the 

preparation of photogeologic maps of 35 salars. This 

study was followed by field examination of 20 salars 

that show a wide variety of morphological and structural features. 

Northern Chile offers a unique opportunity for the 

study of salars, which are exceptionally numerous 

and diversified in size, morphology, and mineralogy. 

Within the large area of interior drainage, covering 

more than 38,000 square miles, there are approximately 100 salars that together occupy about 2,800 

square miles. Hard evaporite crusts alone cover 

more than 1,500 square miles, whereas such crusts 

are comparatively uncommon in the United States. 

Two-thirds of the Chilean salars are high in the 

Andes at elevations of 10,500-16,000 feet, a semiarid 

setting that contrasts sharply with the extremely 

arid coastal desert. Comparison of salars in these 

two areas of distinctly different climates-precipitation, relative humidity, and temperature-gave new 

information about climatic influence on salt crust 

morphology. 

Of two major crustal types recognized in Chilean 

salars, the most prevalent is a hard perennial evaporite crust that is roughly equivalent to the zone of 

chlorides (chiefly halite) . Soft salar crusts in Chile 

are commonly the rough equivalent of the zone of 

sulfates, including chiefly gypsum, mirabilite (or 

thenardite), and ulexite. A unique type of salar crust 

found in the Atacama Desert is a silty nitrate-bearing crust; five salars in northern Chile were mined 

for nitrate during the 19th century. 

Evaporation of both ground water and surface 

water has been important in the formation of salars, 

but crusts resulting from these two sources could 

not be differentiated on aerial photographs. Field 

study, however, revealed morphological and structural features indicative of a surface- or groundwater source and of a variety of climatic and geologic processes. Several features of Chilean salars 

are thought to be better formed there than in other 

desert regions, and a few may be unique to Chile. 

Northern Chile also offers an unusual opportunity 

for study of former climates. Aerial photographs 

clearly reveal evidence of former deep perennial 

lakes in at least 35 basins in the northern Chilean 

Andes where no lakes now exist. The largest and 

deepest of these lakes was probably an arm of Lago 

Minchin, which was chiefly in Bolivia and which is 

estimated to have attained at its greatest extent a 

depth of more than 400 feet, an area of about 10,000 

square miles, and a length of about 300 miles. 

A study of the environment of perennial lakes 

that presently exist in five basins in the Chilean 

Andes provides clues to probable environments of 

the past, when lakes were more numerous. It is concluded from this study that perennial lakes could 

form in nearly all the 67 Andean basins if the mean 

annual rainfall of the region above 10,000 feet increased to 15 inches from its present average of 
64 GEOLOGY OF SALARS, NORTHERN CHILE 

about 8 inches, and if the mean annual temperature 

were about 2°F lower than it is at present. 

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