f

DEPARTMENT OF THE INTERIOR

Hubert Work, Secretary

U. S. GEOLOGICAL SURVEY 

George Otis Smith, Director

Bulletin 790

CONTRIBUTIONS TO THE GEOGRAPHY

OF THE UNITED STATES

1926

MARIUS R. CAMPBELL

GEOLOGIST IN CHARGE

UNITED STATES

GOVERNMENT PRINTING OFFICE

WASHINGTON

1927
CONTENTS

[The letters in parentheses preceding the titles are those used to designate the chapters for advance publication]

Page

(A) Pedestal rocks formed by differential erosion, by Kirk Bryan (published Nov. 27, 1926).__.______..______.__.__.___.__......_ ' 1

Channel erosion of the Rio Salado, Socorro County, N. Mex., by

Kirk Bryan.__________________________________________ 17

(B) The "Palouse soil" problem, with an account of elephant remains 

in wind-borne soil on the Columbia Plateau of Washington, by 

Kirk Bryan (published January 18, 1927)_______________ 21

Index ____________________________________________ __ _ 46

ILLUSTRATIONS

Page

PLATE 1. A, Hillock of basalt columns 6 miles north of Wheeler, Grant 

County, Wash.; B, Pedestal rock formed by mechanical 

disruption of basalt column _____________________________ J2

2. A, B, Pedestal rocks in canyon of Jemez Creek, N. Mex______ 2

3. A, Pedestal rock of sandstone near Seven Lakes, McKinley 

County, N. Mex.; B, Pedestal rock of sandstone near McGillvray's ranch, McKinley County, N. Mex_________________ 2

4. A, Hills of "Palouse soil" rising above the scabland near Hillcrest, Wash.; B, Rolling topography of a "Palouse soil" area 

in Whitman County, Wash.; C, Rolling topography at Old 

Maid Coulee, Wash____________________________________ 34

5. A, Gravel pit in the terrace on Old Maid Coulee, Wash.; B,

Road cut at Fishtrap, Wash..___________________________ 34

6. Photomicrographs illustrating characteristics of soil residual 

from basalt, supposed loess, and loess: A, Decomposed basalt 

from road cut north of Colfax, Wash.; B, Typical tawny 

yellow clay of the lower part of the "Palouse soil" from road 

cut north of Colfax, Wash.; C, Typical brownish upper layer 

of the "Palouse soil" from road cut south of Spangle, Wash.; 

D, Loess from Council Bluffs, Iowa______________________ 34

7. A, Lower jaw of Elephas columbi from wind-borne soil on the 

Columbia Plateau, Wash.; B, Rolling hills of Columbia Plateau 

at elephant locality, 15 miles southwest of Kahlotus, Wash.; 

C, Road cut on Pleasant Prairie, north of Spokane, Wash____ 34 

FIGURE 1. Diagram illustrating differential rain wash on a pedestal rock 

consisting of an impervious block resting on an easily eroded 

mass below.--_-------_-_-_-__-_---____-______________ 8
CONTRIBUTIONS TO THE GEOGRAPHY OF THE

UNITED STATES, 1926

PEDESTAL ROCKS FORMED BY DIFFERENTIAL EROSION

By KIRK BRYAN

INTRODUCTION

Isolated rocks consisting of a larger mass above resting on a 

smaller base or pedestal and known generally as pedestal rocks form 

one of the most spectacular types of natural monuments. The processes by which such forms are produced are doubtless as numerous 

as the agents of rock destruction, and it is probable that all the varied 

methods of weathering and of abrasion play a part in the formation 

of some of these rocks. In two preceding papers 1 of these contributions the origin of certain pedestal rocks has been attributed to 

abrasion of the base of the rock by running water or to rain wash 

and differential weathering. In this paper additional examples of 

rocks formed in arid climates by differential weathering are described. The nice cooperation of chemical and mechanical weathering in Washington and the differential weathering of sandstone in 

New Mexico produce rocks that can, by detailed study, be distinguished from rocks described in the preceding papers that are due 

to differential rain wash or to abrasion by running water.

Pedestal rocks may be produced by the abrasive action of the water 

and suspended matter in streams, or by the work of waves of seas or 

lakes, or by the scour of wind-driven sand. The favorable conditions 

for the production of the form in a stream are (1) the introduction 

of a block of rock into the channel by its fall from above or by the 

lowering of the channel on both sides of a mass of rock in place; (2) 

a fairly constant flow of water without excessive floods which might 

in their violence snap off the pedestal; (3) sufficiently short duration 

of the process.

Abrasion and solution by streams are given by Martel 2 as the sole 

causes of pedestal rocks, of which he has described a large number in

1 Bryan, Kirk, Pedestal rocks in the arid Southwest: U. S. Geol. Survey Bull. 760, pp. 

3-11, 1925; Pedestal rocks in stream channels: Idem, pp. 123-130. See also Bryan, Kirk, 

Pedestal rocks: Eng. and Min. Jour. Press, vol. 119, pp. 172-173, 1925.

2 Martel, E. A., L'6rosion des gres de Fonlainebleau: Services carte g6ol. France Bull. 

127, 1910. In this bulletin several earlier papers dating back to 1886 are summarized.

1
2 CONTRIBUTIONS TO GEOGEAPHY OF UNITED STATES, 1926

various parts of France. He vigorously combats the idea that rain 

and wind erode such rocks, and he describes three rocks whose form 

has been produced by stream action a rock in the bed of Velon 

River 3 that stands in the bottom of a partly destroyed pothole; a rock 

in a limestone cavern at Furfoos, Belgium,4 protected from weather, 

rain, and wind, but so fragile that it can not be subject to abrasion 

and must be due almost wholly to solution; and a rock in Gibbon 

Eiver, Yellowstone National Park,5 also described by me.6 He contends that rivers with strong and turbulent currents once flowed at 

the level of the plateaus of France and particularly over the plateau 

of Fontainebleau. Although these streams date back to Pleistocene 

or Pliocene time, their channel features still persist in the form of 

potholes, arches, and pedestal rocks. In limestone areas subterranean 

streams flowing through caverns also produce these forms, partly by 

solution and partly by abrasion, and subsequently erosion has brought 

them to the light of day.

The effectiveness of stream erosion in the making of such rocks is 

somewhat limited, as set forth above, and this conclusion is confirmed by the rarity of occurrences in the beds of present streams. 

Although the three examples cited by Martel seem entirely valid, his 

position in regard to other rocks in France represents a point of view 

which is not concurred in by others,7 who attribute the rocks of 

Fontainebleau and Montpellier-le-Vieux to the work of weathering 

and rain wash.

The formation of isolated masses by the abrasive and plucking 

action of waves against a cliff is common, and such masses, to which 

the term stack is applied, have been described by a number of 

writers.8 The notched stack is such a mass somewhat undercut by 

the waves. Ordinarily the notch is on the side exposed to the waves, 

but on some stacks the notch, because of a weakness of the rock at

3 Martel, B. A., op. cit, pp. 15-16, fig. 16.

4 Broeck, E. van den, Martel, E. A., and Rahir, E., Cavernes et les rivieres souterraines 

de la Belgique, vol. 2, pp. 822-824, fig. 234, 1910.

5 Martel, B. A. [Concerning the torrential origin of peduncular rocks] : Compt. Rend., 

vol. 159, pp. 87-89, 1914.

8 Bryan, Kirk, Pedestal rocks in stream channels: U. S. Geol. Survey Bull. 760, p. 127, 

1925.

7 Douvill6, H., Etude sur les gres de la forSt de Pontainebleau : Soc. g6ol. France Bull., 

3° se"r., vol. 14, pp. 471-481, 18S6. Barre", 0., Le relief de la forSt de Fontainebleau: 

Annales de geographic, vol. 11, pp. 295-314, 1902. De Lapparent, A., Legons de ge"ographie physique, 3d ed., pp. 90-91, Paris, 1907. Haug, E., Traite" de geologic, vol. 1, 

p. 379, Paris, 1921.

8 Geikie, Archibald, The scenery of Scotland, etc., pp. 67, 71, London, 1887. Fairbanks, 

H. W., Practical physiography, p. 411, fig. 342, Boston, 1906. Arber, E. A. N., The 

coastal scenery of North Devon, pp. 107-108, London, 1911. Atwood, W. W., Geology 

and mineral resources of parts of the Alaska Peninsula: U. S. Geol. Survey Bull. 467, 

p. 92, pis. 5, B; 9, B; and 12, B, 1911. Hobbs, W. H., Earth features and their meaning, 

p. 234, figs. 252-254, 1912. Johnson, D. W., Shore processes and shore-line development, 

pp. 278-279, pis. 34, 35, New York, 1919. Cotton, C. A., Geomorphology of New Zealand, 

pt. 1: New Zealand Board Sci. Art. Manual 3, p. 378, fig. 369, 1922. Dalmage, V., PostPliocene volcanics of the British Columbia coast: Jour. Geology, vol. 32, p. 41, fig 4, 

1923.
U. S. GEOLOGICAL SURVEY BULLETIN 790 PLATE 1

A. HILLOCK OF BASALT COLUMNS 6 MILES NOHTH OF WHEELER, GRANT 

COUNTY, WASH.

A column on the left has the form of a pedestal rock. Photographed in 1923

B. PEDESTAL BOCK FORMED BY MECHANICAL DISRUPTION OF BASALT

COLUMN

: . _ Photographed iu 1923 ' . ".
T. S. GEOLOGICAL SURVEY BULLETIN 790 PLATE 2

A. SANDSTONE BLOCK RESTING ON PEDESTAL OF SHALE DETACHED FROM 

THE BANK OF WHICH IT ONCE FORMED A PART

B. SANDSTONE BLOCK RESTING ON RUBBLE OF OLD TALUS ELSEWHERE 

STRIPPED FROM A SHALE SLOPE

PEDESTAL ROCKS IN CANYON OF JEMEZ CREEK, N. MEX. 

Photographed in 1923
IT. S. GEOLOGICAL SURVEY BULLETIN 790 PLATE 3

A. 1'EDliSTAL HOCK OF SANDSTONE NEAR SEVEN LAKES, McKINLEY 

COUNTY, N. MEX.

Photographed in 1921

B. PEDESTAL ROCK OF SANDSTONE NEAR MoGILLVRAY'S RANCH, McKINLEY

COUNTY, N. MEX.

Photographed in 1924 ~~" .. .
PEDESTAL ROCKS FORMED BY DIFFERENTIAL EROSION 3

the position of greatest scour, extends all the way around the stack. 

Such notched stacks have the same form as pedestal rocks. Obviously, these rocks are structurally weak and are easily destroyed 

by the high waves of great storms. Direct abrasive action of windblown sand is asserted by a number of writers ° to be the agent in 

the formation of pedestal rocks in deserts. Neither the descriptions 

nor the photographs presented by these writers are wholly convincing, except those of a rock on the coast of the Red Sea described by 

Wade 10 and of one in Southwest Africa described by Harger.11 

There is no inherent reason why the form can not be produced by 

this process, provided that winds and sand operate for a sufficient 

length of time on a favorably located mass.

The pedestal should show the marks of abrasion by wind-blown 

sand, but the possibility of polish by the pelts of grazing animals 

should be eliminated, as Karl Walther 12 has pointed out in describing a pedestal rock of granite which was produced by differential 

weathering in the plains of Uruguay.

Pedestal rocks in areas having various types of climate are due 

to differential weathering, and the object of this paper is to describe 

the particular processes of differential weathering which have produced certain pedestal rocks in areas having climates that differ 

in type but are comparatively arid. The examples from the State 

of Washington were studied incidentally in the course of a geologic 

examination of the Columbia Basin irrigation project in 1923. The 

rocks in the canyon of Jemez Creek, N. Hex., were seen while I 

was on leave in the same year, and the rocks in McKinley County, 

N. Mex., were visited during a geologic study of the recent deposits 

of Chaco Canyon for the National Geographic Society in 1924.

PEDESTAL ROCK IN BASALT

The pedestal rock in basalt here described is by no means perfect 

in form, but it is due to so curious a combination of circumstances 

that a description will doubtless be interesting to those concerned 

with the processes of arid regions. The rock lies at the north end of 

a small hillock 12 miles southwest of Adrian and 6 miles north of 

Wheeler, Grant County, Wash. This locality is in the west-central 

part of the Columbia Plateau. Quincy Basin, a structural depression, lies to the west, and the lavas of the plateau in this vicinity dip

0 A fairly complete list is given in U. S. Geol. Survey Bull. 760, p. 1.

10 Wade, Arthur, Some observations in the eastern desert of Egypt, -with considerations 

bearing on the origin of the British Trias (with discussion) : London Geol. Soc. Quart. 

Jour., vol. 67, p. 248, pi. 14, fig. 2, 1911.

u.Harger, H. S., Denudation in South Africa: South Africa Geol. Soc. Proc., 1913, p. 

xxxiv, and especially fig. 1.

12 Estudios geomorfologicos y geolSgicos: Montevideo Inst. hist. geog. Revista, vol. 4, 

p. 109, footnote, 1924.
4 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1&26

almost insensibly westward and pass under the gravel and sand that 

form this plain. Several waterless gorges extend westward from 

the higher land and fade out in the basin. Near the mouth of one 

of these gorges. Black Rock Coulee, long ago deserted by the 

glacial waters that excavated it, there is an area with numerous 

rocky hillocks projecting from the plain. The irregular rock surface, of which the hillocks are the high points, was doubtless carved 

by the glacial waters from Black Rock Coulee. Over this floor 

wind-blown dust from the flats of Quincy Basin or rehandled loess 

from the surrounding plateaus has settled.

The hillock with the pedestal rock consists of a group of basalt 

columns each of which is from 18 inches to 3 feet across. The columns are mostly six-sided and are unusually even and symmetrical. 

As shown in Plate 1, A, each column is separated from the neighboring ones by a space about 2 inches wide, yet each column, though 

it has the irregularities normal to such columns, fits its neighbors 

and evidently has not been displaced since its formation. At the 

base of the columns and below the ground surface the rock is continuous from column to column except for a medial crack. For an 

inch on each side of this crack the rock is soft, is greenish gray with 

rusty crevices, and gives the appearance of having suffered from 

chemical decomposition. The space between the columns, above 

ground, is obviously due to the removal of rock weakened in the same 

way. The projecting columns, though diminished in size, are hard 

and sound, and their faces are smooth and regular. They are little 

affected by corrosive processes but suffer disruption by spalling. 

The dense, tough rock breaks in spalls and chips, and to this spalling 

is due the pedestal rock shown at the left in Plate 1, A, and in more 

detail in Plate 1, B. This column has two incipient cross joints, and, 

as is well shown in Plate 1, B, spalling to these joints has produced 

the narrow neck that is surmounted by a block the full size of the 

column. The neighboring column is suffering from the same process, and some of the adjacent columns also show spalling from the 

corners. A few columns have lost from the sides, as well as from 

the corners, numerous thin rock chips, which litter the ground. 

These chips and the larger fragments broken from the corners 

appear to be fresh rock and ring when struck by the hammer.

Chips collected from the surface and dug out from between the 

columns have been studied by Clarence S. Ross, who has furnished 

the following statement:

The chips from the columnar basalt when studied under the microscope, 

both in thin section and as small grains embedded in immersion oils, show 

interesting characteristics, some of which were not suspected before examination. The rock is a normal basalt but little altered and is composed of calcic 

plagioclase, augite, and sparse olivine and magnetite.
PEDESTAL BOOKS FORMED BY DIFFERENTIAL EROSION 5

The chips collected above ground have a dull weathered and pitted surface, 

but 1 millimeter below the surface they appear to be' fresh, and they have the 

sharp metallic ring of a fresh rock.

The chips collected below the ground surface have a dirty greenish-gray 

appearance, and the laminae and cracks are filled with alteration products, 

among which opal is the most abundant. They do not ring but give a dull 

sound when tapped, and they present an appearance of rock decay.

In the chips collected above ground the plagioclase grains are entirely 

unaltered chemically, the augite grains are nearly as fresh, and the sparse 

olivine is only partly decomposed. A red-brown mineral secondary to olivine 

is present, but it was probably developed during the final cooling of the rock 

and is not a product of later weathering. A very small amount of limonitic 

material has developed which gives the rock a rusty appearance under the 

hand lens. This material lies in the cracks and cleavage planes of the minerals 

and as viewed under the microscope is a pale yellow-brown stain which accentuates the fractures and cleavage planes. The most striking characteristic 

is the development in the plagioclase and augite of countless small fractures, 

which are far more abundant and conspicuous than in a fresh basalt. On 

the surface of the chips minerals that appear nearly fresh under the microscope 

have become so fragile that they can not be picked up with the forceps, but 

. just below the surface, although the fractures are nearly as conspicuous, the 

minerals are not so fragile. The fractures in general cut across the augite 

and olivine grains in random directions, but in most of the plagioclase grains 

they make an angle of 45° with the cleavage or follow a cleavage plane for 

a distance and then break across at an angle of approximately 45° to another 

cleavage plane, so as to form a rather regular network of fractures.

The minerals of the rock chips collected below the ground surface are 

surprisingly fresh considering the appearance of the rock in the hand specimen. The plagioclase grains are unaltered chemically, but the augite and 

olivine grains show distinctly more Alteration than these minerals in the chips 

collected above ground. Both the plagioclase and the augite have only a 

few more fractures than are characteristic of the minerals of normal fresh 

basalt, and they do not have the abundant fractures shown by these minerals 

in the chips collected above ground.

The greater amount of weathering by chemical decomposition in 

the rock chips collected below the ground surface observed by Mr. 

Boss is confirmed by chemical tests carried out in the chemical 

laboratory of the Geological Survey by J. G. Fairchild. The results 

may be tabulated as follows:

Partial analysis of weathered basalt from hillock 6 miles north of Wheeler,

Grant County, Wash.

Ferrous iron (FeO) -..--.. _____ . _ . ________ . ______ ..... ____ ..

Sample

taken

above

ground

Per cent

10.3

1.06

Sample

taken

below

ground

Per cent

0.24

2.32

The relative loss in content of ferrous iron of the rock chips from 

below the surface indicates that the olivine and augite have begun to
6 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

break down, as is to be expected in the decay of basalt^ and the increase in water content indicates that hydrous clayey minerals have 

been formed as a result of the decomposition of these minerals and 

perhaps also of the plagioclase, although under the microscope this 

mineral gives no sign of decomposition.

The intimate fracturing of the mineral grains of the rock chips 

from the surface brought out by Mr. Boss's study can be safely attributed to mechanical disruption, because the absence of decomposition products except for the small amount of iron oxide testifies to 

the almost complete lack of chemical change. The physical forces 

that can have caused the disruption are frost action and thermal 

expansion and contraction under the diurnal and annual fluctuations 

of air temperature. It seems .improbable that sufficient water could 

penetrate into the mass of these otherwise unaltered mineral grains 

to disrupt them on its expansion in freezing, though no data are 

available in support of this contention. The fractures are, however, 

of. a type that should arise if the grains were subjected to the stresses 

due to thermal expansion or contraction when at the same time they 

were confined by and stressed by other grains affected by the same 

forces. As the diurnal changes of air temperature are not only more 

numerous but because of their short period produce greater ranges of 

temperature in adjacent parts of the rock, they have doubtless been 

more effective than the annual changes in temperature in producing 

the cracks. It should also be noted that just below the ground surface 

the fracturing is absent, although there the annual changes in temperature should be just as effective.

The spalling of small chips and larger masses, to which the pedestal rock is largely due, is also a mechanical process. Spalling of this 

type is ordinarily attributed to thermal expansion and contraction, 

but Blackwelder 1S has recently expressed the doubts which it is 

evident from a review of the literature have lingered in the minds 

of geologists as to the validity of this process.

In this relatively arid locality conditions are favorable for numerous and rapid changes in air temperature, which, if such changes 

can disrupt rock, should produce the spalling that has been observed. 

Even if the changes in temperature of this locality are insufficient 

to disrupt a rock of normal strength the outer part of these basalt 

columns has already suffered from a minute internal rupture of its 

component minerals and therefore lacks part of the original strength 

and may have other quite distinct physical properties.

Frost action also can not be wholly eliminated, because the locality 

has a cold winter during which moisture that had collected in the 

fractures of the mineral grains might freeze and cause the spalling.

13 Blackwelder, Eliot, Exfoliation as a phase of rock weathering: Jour. Geology, vol. 33, 

pp. 793-806, 1925.
PEDESTAL ROCKS FORMED BY DIFFERENTIAL EROSION 7

The relatively small amount of chemical weathering observed below the ground surface and between the columns may possibly be 

due to forces operative in the past. A little decomposition of this 

sort is evident in all the outcrops of basalt in the Columbia Plateau. 

Cliffs that are thought to have been formed by streams issuing from 

the ice of Wisconsin time appear to consist of fresh rock, but a close 

inspection shows that they have many zones of soft decomposed rock 

along vertical joints. The minerals that once filled the vesicles of 

the basalt have been leached out, and bands of opal in the cracks 

are more or less decomposed. Ordinarily, in the Columbia Plateau, 

surfaces formed in pre-Wisconsin time are underlain by rock that is 

softened and discolored by unmistakable chemical weathering. It 

may be that the chemical weathering of this locality began in the 

early Pleistocene and has been inherited from a time preceding the 

occupation of Black Bock Coulee by glacial waters,14 which have removed at this place only a moderate thickness of rock. On the other 

hand the glacial channel in Black Kock Coulee may belong to the 

intermediate glaciation (Spokane of Bretz) or some earlier ice advance, and if so there has been ample time for chemical weathering 

to take place since the channel was formed. Chemical weathering 

may even be going on at the present time, for, although the climate 

is arid, the fine-grained soil is retentive of moisture.

The rock has formed in an arid climate, within the " dry spot" 

of Washington, a nearly circular region about 50 miles in diameter, 

in which the annual rainfall is less than 8 inches. The published 

observations of the United States Weather Bureau at Wheeler, 6 

miles to the south and at about the same altitude, indicate, from an 

incomplete 7-year record, a mean annual precipitation of 7.12 inches. 

Most of this precipitation takes place in the winter months, November to February, though showers are also common in May and June. 

The moisture stored in the ground in winter, together with the spring 

rains, is sufficient to support sagebrush and a fair cover of grass. 

The vegetation has been sufficiently luxuriant to retain the fine loesslike soil. The capacity of this soil to hold moisture may, as already 

stated, provide suitable conditions below the ground surface for the 

small amount of chemical decomposition that has taken place between 

the columns.

Above the ground surface, however, the rain readily washes away 

the parts of rock that have been chemically decomposed even in a 

minor degree. During the long dry summer insolation has full play,

"Bretz, J. H., Glacial drainage on the Columbia Plateau: Qeol. Soc. America Bull., 

vol. 34, pp. 573-608, 1923. The map of fig. 1 does not show Black Rock Coulee as a 

glacial channel. See, however, Bretz, J. H., The channeled scablands of the Columbia 

Plateau: Jour. Geology, vol. 31, pp. 617-649, 1923, especially p. 644 and pi. 3.

33377° 27 2
8 CONTRIBUTIONS TO GEOGEAPHY OF UNITED STATES, 1926

and the alternate contraction and expansion of the dense fine-grained 

basalt of the columns causes near the surface intimate fracturing of 

the component minerals. The same forces tend to bring about the 

flaking of chips from the sides and the spalling of the corners of the 

columns, but here frost action may come into play and may possibly 

be the dominant factor in disrupting the rock.

Thus this pedestal rock has attained its form by the action of both 

chemical and mechanical weathering on a basalt column having two 

incipient cross fractures. The combination of conditions necessary 

for the production of this rock is not wholly exceptional, for 3 miles 

northwest of Adrian there is a somewhat similar pedestal rock 

formed in an identical manner.

 x -"-" 

" S/ope over which material eroded from 

pedestal is transported by water of 

inner film_______________

PIGDKE 1. Diagram illustrating differential rainwash on a pedestal 

rock consisting of an impervious block resting on, an easily 

eroded mass below

DIFFERENTIAL, RAINWASH

The violent showers characteristic of most arid climates will produce pedestal rocks by differential rainwash where blocks of impervious material rest on easily eroded material. The mechanism of 

this process was observed near Lees Ferry, Ariz., and has been described in an earlier paper.15 The process is shown diagrammatically 

in Figure 1. The main work of producing the pedestal is done by the 

drip curtain, which excavates an annular groove around the rock. 

An inner film of water, however, clings by adhesion to the overhang 

of the rock and reaches the pedestal. It is largely the work of this 

film which erodes and thins the pedestal back of the drip curtain. 

In the rain observed at Lees Ferry the inner film reached just to the 

pedestal and wet its top. That this inner film may not only reach the 

pedestal but may, under suitable circumstances, cause erosion is evident from a pedestal rock in the canyon of Jemez Creek between the

« Bryan, Kirk, U. S. Geol. Survey Bull. 760, pp. 1-11, 1925.
PEDESTAL ROCKS FORMED BY DIFFERENTIAL EROSION 9

towns of Canyon and Jemez Hot Springs, N. Mex., about 150 miles 

east of Lees Ferry, Ariz. The rock consists of a loose block of 

dense red sandstone, derived from outcrops farther uphill, that rests 

on a pedestal of red shale, as shown in Plate 2, A. On the face of the 

pedestal is a vertical roll'of hardened mud similar in form and origin 

to the rolls of mud that form on the inside of an adobe house when 

the roof leaks. Obviously, the inner film of water traveling on the 

overhang, as shown in Figure 1, has reached and eroded the pedestal. 

Such a movement of water can have little scouring action, but if continued will lead to the removal of any material on the pedestal that 

is already loosened by weathering.

A rock near by (pi. 2, B) consists of a block of sandstone resting on 

a mass of rubble that in turn rests on red shale. The rubble and, 

doubtless, also the underlying block are the last remnants of a talus 

that once mantled the mountain side. The block has partly protected the underlying rubble in the process of differential erosion by 

rainwash, but the vertical grooves in the rubble bear mute testimony 

to erosion by water dripping over the face of the pedestal as an inner 

film. At the point marked " a " the rubble overhangs and protects 

the red shale which forms the lower 8 inches of the pedestal. The 

rubble is therefore more resistant to rainwash than the shale.

The climate of the area in which these rocks occur is not very 

different from that at Lees Ferry, except for lower temperature and 

greater precipitation, due to an altitude 2,500 feet higher. The 

mean annual rainfall amounts to 17.13 inches at Jemez Hot Springs, 

according to the record of the United States Weather Bureau over 

a period of 14 years, as compared to 5 inches, the estimated mean 

at Lees Ferry. This mean rainfall of 17.13 inches places the 

locality well within the arid zone as usually considered, yet it is 

evident that the rock shown in Plate 2, B, differs from the form 

of natural monument called earth pyramid, earth pillar, or demoiselle, only in having a larger block in proportion to the size 

of the pedestal. There seems, therefore, to be no essential difference 

in origin or method of erosion between earth pillars and pedestal 

rocks of this type. Yet earth pillars are generally admitted to be 

normal forms of erosion in humid regions, although they are 

doubtless less numerous there than in arid regions, where a slower 

rate of erosion gives each of them a longer life.

DIFFERENTIAL SAPPING

The overlying block in a pedestal rock formed by differential rainwash is relatively impervious to rain. If the upper block is porous, 

however, and absorbs part or all of the rain that falls on it, the 

circulation of water within the mass of the rock promotes weather-
10 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

ing by solution. Sandstone is particularly susceptible to attack 

by water absorbed from rain. Generally, the water dissolves the 

cement and, traveling on original lines of easiest passage, emerges 

at the sides or base of the rock, where it runs out or is evaporated. 

At or near the point of emergence the rock crumbles into its original 

sand grains, which fall away or are carried off by rainwash. The 

intricacies produced by this process are truly marvelous. In general 

an excavation or eating back of the original mass takes place, and 

the process will here be called differential sapping.

Although characteristic also of the weathering of sandstone in 

humid regions the forms produced by this process in arid regions 

have been attributed by many to wind erosion. Gregory,16 however, 

has invoked differential sapping as the method of formation of 

niches under dry waterfalls, of rock shelters, of windows, and of 

arches in sandstone in the dry climate of the Navajo country. Certain rock shelters and niches 1T in the Papago Saguaro National 

Monument of southern Arizona, where the mean annual rainfall 

is about 7 inches, have also been ascribed to this process.

PEDESTAL HOCKS IN SANDSTONE 

LOCALITY AND CLIMATE

In northwestern New Mexico, in the areas underlain by sandstone 

and shale of Upper Cretaceous age, pedestal rocks are numerous. 

At each outcrop of sandstone one or more pedestal rocks may be 

found. These rocks are special forms of those monuments of erosion 

customarily isolated in the recession of cliffs. Their shape is due to 

the cooperation of a variety of structure in the original rock and 

several processes. The rocks that are most symmetrical in form are 

due to a nicety in this cooperation that may be considered fortuitous, but the great numbers of pedestal rocks which exist in this 

region indicate that certain conditions are dominant. The nature of 

the rock structure and the processes which act upon it in the production of pedestal rocks in the southern part of the San Juan Basin, 

near Crown Point, McKinley County, N. Mex., will be described 

in the following paragraphs.

The climate of the area is moderately arid and marked by cold 

winters and hot summers. An incomplete weather record extending 

over 11 years at Crown Point, where the altitude is 6,800 feet, as 

published by the United States Weather Bureau, gives a mean annual precipitation of 10.9 inches. In the five consecutive years for

18 Gregory, H. E., Geology of the Navajo country, a reconnaissance of parts of Arizona, 

New Mexico, and Utah : U. S. Geol. Survey Prof. Paper 93, pp. 133-134, 1912.

17 Bryan, Kirk, The Papago country, Arizona, a geographic, geologic, and hydrologic 

reconnaissance, with a guide to desert watering places: U. S. Geol. Survey Water-Supply 

Paper 499, pp. 91-93, 1925.
PEDESTAL ROCKS FORMED BY DIFFERENTIAL EROSION 11

which this record is complete the precipitation ranged from 5 to 

16.99 inches, indicating to some extent the great droughts and correspondingly wet years to which the area is subject. A large part of 

the winter precipitation is in the form, of snow, and in the spring 

the ground is usually sufficiently moist to permit the growth of 

vegetation. In May and June rain sufficient to wet the ground, is 

rare. In July the so-called rainy season begins. Heavy cumulus 

clouds drift over the country, and from these clouds fall violent local 

rains or cloudbursts. The areas in which these rains fall are sometimes small, but the heavier rains usually cover extensive areas. 

From a half to two-thirds of the annual precipitation falls during 

the rainy season, but this period of rain is uncertain in time and 

place. In years of generally high rainfall some areas receive little 

rain, and in many years the summer rains are delayed until September. In spite of the severity of these conditions for the growth 

of plants, the loamy and clayey soils developed on shale or on the 

overflow areas of ephemeral streams have a good growth of deeprooted perennial grass, which makes its principal growth during the 

summer rains. The sandstone beds usually crop out as bare rock and 

have little soil except patches of wind-blown sand. Scanty grass 

grows on the sand, but the hardy juniper (scrub cedar) thrives in 

scattered groves, even on the bare rock.

The mean annual temperature at Crown Point so far as determined is about 50° F. The absolute range in temperature, however, 

is large, from 8° on January 2, 1919, to 95° on July 1, 1917. 

The daily range, especially early in the summer, is also large, 

probably amounting to as much as 60° or TO 0 .

This relatively severe climate, with its long periods of drought 

and violent rains, hot summers and cold winters, warm days and 

cold nights, has corresponding effects on erosive processes.

THE BOCKS

One of the most picturesque pedestal rocks of this area stands 

about half a mile off the road from Crown Point to Chaco Canyon 

near Seven Lakes. As shown in Plate 3, A, this rock rises from a 

small knoll in an area with a sparse vegetation of small bushes, 

grass, and junipers. The knoll lies in a small amphitheater in low 

cliffs of horizontal sandstone that is identical with the material of 

the pedestal rock. The rock is thus an erosion remnant between 

small valleys working headward into the cliffs and is remarkable 

only in the details of its form. An inspection of the photograph 

shows that joint faces are not entirely obliterated from the massive 

sandstone at the top, and the implication is that the isolation of the 

rock is due to erosion by .weather and streams, along vertical joints. 

The remarkably slim pedestal is composed of laminated, somewhat
12 CONTRIBUTIONS TO GEOGEAPHY OF UNITED STATES, 1026

clayey sandstone, and the constricted portion halfway up is of 

similar material. The capping sandstone is massive, as are the 

other projecting portions of the mass. It seems obvious that the 

laminated and clayey beds have suffered more from weathering than 

the remainder of the rock, and that the form is due to the distribution of the less resistant beds and the summation of the differences in 

the rate of weathering. That differential sapping, as denned on 

page 10, is the most active process, seems evident; first, because of the 

selective work against certain beds, which is effective irrespective 

of their thickness or position above the ground surface, and second, 

because at the time of visit, a few days after a rain, the surface of 

the slimmest part of the pedestal was damp, whereas that of the 

rest of the rock was dry and powdery.

Differential rain wash can not be solely accountable for this rock, 

because the differences in resistance of the different sandstone beds 

are too slight and the porous upper mass must absorb at least part 

of every rainfall. However, it seems likely that the inner film of 

water that creeps over the rock face during rainstorms is effective 

in removing loosened grains from all the intricate reentrants of the 

mass. Doubtless many of these loosened grains simply fall by 

gravity, and others are perhaps shaken loose during high winds. 

That the scour of sand carried by wind has any appreciable effect 

can be denied, for the base of the rock is too high above the ground 

for wind scour to be effective. All authorities are agreed that 2 to 3 

feet above the ground surface is the limit of effective wind scour.18

The rock illustrated in Plate 3, B, stands near the road from Crown 

Point to Chaco Canyon, about 20 miles northeast of Crown Point. 

To the right of the view there is a rounded boss of sandstone eroded 

from the same horizontal sandstone bed, but the pedestal rock stands 

detached in a plain of sandy soil that within the area of the view 

merges into an alluvial sandy loam. Apparently the rock was once 

a mass approximating a cube in shape that was isolated along vertical joints, but the present form seems to be due to differential sapping. The upper part of the rock is separated from the remainder 

by a bedding plane, and it seems fair to assume that this upper 

sandstone has always been somewhat harder than the remainder of 

the rock. It is porous, however, and has a crumbly surface. Obviously it absorbs rain water, which emerges lower down from the 

pores of the sandstone of the pedestal. The surface of this lower 

portion is notably soft and friable, particularly near the ground. 

Here individual sand grains are loosened and fall by gravity or are

18 Among others, see Hobbs, W. H.. The erosional and degradational processes of deserts, 

with especial reference to the origin of desert depressions: Assoc. Am. Geographers Annals, vol. 7, p. 33, 1918. .
PEDESTAL SOCKS FOKMEiD BY DlFPEllENTlAL EROSIOtf 13

washed off by the inner film during rains. Not only does the pedestal 

disintegrate into sand by the relatively slow solution of its cement 

but periodically large pieces fall off, as is attested by their presence 

at the base of the rock and by the scars left on the pedestal into which 

some of them can almost be fitted. It seems likely that frost action, 

when the pedestal is saturated after rains, aids in detaching these 

blocks. The wide range in temperature and the severity of the winter 

have been noted above.

Between the scars of recent falls there are somewhat more ancient 

surfaces that are minutely pitted. Each pit is about three-eighths 

of an inch in diameter and half an inch deep. Some of them contain dead insect pupae. It seems evident that wasps bore these holes 

as nests for their young under the overhang of the rock, where they 

are protected from the direct impact of rain. Thus animals contribute, in slight degree, to the erosion of the rock.

It seems impossible that wind scour can have had any important 

part in the formation of this rock. The pulverulent surface of the 

pedestal testifies to differential sapping; the scars, to frost action; 

and the pitted surfaces, to insect erosion. None of these surfaces 

could retain their characteristics under the sand blast, and they are 

in marked contrast to the firm, harsh surfaces of similar rocks in the 

region that are unquestionably scoured by wind-driven sand. The 

surrounding area is sandy, as might be expected where the local 

debris is.all derived from the erosion of sandstone. Near by there 

are small accumulations of wind-blown sand, 6 inches to 2 feet thick, 

which are, however, more or less prevented from moving by the 

growth of grass. Near the pedestal rock sand is not moving in large 

amount or with violence, else the grass and sagebrush would be cut 

away, and the rock fragments lying at the foot of the pedestal rock 

would be shaped by wind scour.

PEDESTAL. ROCKS IN HUMID REGIONS

The pedestal rocks described in this paper are all located in arid 

regions, yet the processes by which they have arisen are operative 

in humid regions. From a review of geologic textbooks one would 

gain the impression that pedestal rocks are characteristic of arid 

regions and do not occur in more humid lands. Aside from notched 

stacks on coasts and pedestal rocks formed in streams, whose origin 

is apparently independent of climate, a considerable number of 

pedestal rocks in humid regions have been described. In England 10

19 Hughes, T. McK., On some perched blocks and associated phenomena: Geol. Soc. 

London Quart. Jour., vol. 42, pp. 527-539, 1886 ; Notes on the geology of parts of Yorkshire and Westmoreland: Geol. Polytechn. Soc. West. Rid. Yorkshire I'roc., vol. 4, p. 574, 

1867. Bonney, T. G., The work of rain and rivers, p. 18, Cambridge Press, 1912.
14 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

and Ireland 20 certain pedestal rocks consist of glacial erratics of 

compact and insoluble rocks resting on limestone. Solution of the 

limestone except where partly protected by the erratic block has produced the forms. Estimates 21 of the age of the pedestal rocks and 

therefore of the time since glaciation, by comparison of the height 

of the pedestal with the rate of solution of limestone, have not been 

wholly satisfactory.

The mushroom rocks of New Ked sandstone in Devonshire are 

thought by Kinahan 22 to be in part due to the work of rain driven 

horizontally by the wind, and the sandstone crags of Kinder Scout 23 

provoked a discussion as to the relative effect of the scour of winddriven sand and of differential erosion, and apparently no later investigator has published a definite conclusion.

In Indiana,24 Illinois,25 Arkansas,20 and Wisconsin 27 are good 

examples of pedestal rocks that may be attributed to differential 

weathering and the subprocesses differential rainwash and sapping.

The life oof pedestal rocks in humid regions is relatively short 

because of the rapidity of rock decay and, in the colder countries, 

because of the increased effectiveness of frost action due to the presence of moisture. Not only are the forms less persistent, but the 

presence of vegetation inhibits rainwash and much of the vertical 

cutting of minor streams, so that the rocks ordinarily occur as the 

result of exceptional conditions, such as the imposition of blocks of 

dense insoluble stone on limestone, or else in areas of porous sandstone 

and limestone. The erosion forms of porous sandstone in humid 

lands reproduce many of the spectacular features of arid regions, 

because areas of such rock resemble arid regions in having a scanty, 

sterile soil, a sparse vegetation, and a low water table. These features 

are well brought out in the literature on the Fontainebleau sandstone 

already referred to and in numerous works on the Quadersandstein 

and Buntsandstein areas of Germany. Similarly, limestones, particularly in areas having the Mediterranean type of climate, may

20 Kinahan, G. H., Valleys and their relation to fissures, fractures, and faults, pp. 53-54, 

London, 1875. Wynne, A. B., Notes on some physical features of the land formed by 

denudation : Ireland Roy. Geol. Soc. Jour., vol. 1, p. 258, 1867.

21 Mackintosh, D., Results of observations in 1882 on the position of. boulders, etc. 

(abstract with discussion) : Geol. Soc. London Proc., Feb. 21, 1883, p. 67. 

^Kinahan, G. H., op. cit, p. 83.

23 Discussion of paper by Enys, J. D., Geol. Soc. London Quart. Jour., vol. 34, pp. 

86-88, 1878.

24 Dryer, C. H., Jug Rock, near Shoals, Ind.: Indiana Acad. Sci. Proc. for 1898, pp. 

268-269, 1899. Logan, W. N., Geologic conditions in the oil fields of southern Indiana: 

Indiana Dept. Conservation Pub. 42, fig. 1, 1924.

=3 Bonnoll, Clarence, The variety of physiographic material in a few counties of southern 

Illinois : Illinois Acad. Sci. Trans., vol. 9, p. 207, 1917.

20 Hopkins, T. C., Marbles and other limestones : Arkansas Geol. Survey Ann. Rept. for 

1890, vol. 4, p. 343, pi. 17, 1893.

"Alden, W. C., The Quaternary geology of southeastern Wisconsin: U. S. Geol. Survey 

Prof. Paper 106, p. 4, pi. 16, A, 1918.
PEDESTAL BOOKS FORMED BY DIFFERENTIAL EROSION 15

produce somewhat similar forms, although in climates like that of 

the eastern United States areas of this type of rock are usually 

mantled by a deep soil.

CONCLUSIONS

The foregoing description of pedestal rocks in the widely separated 

States of Washington and New Mexico calls attention to the variety 

of processes involved in the formation of these minor but distinctive 

forms and emphasizes the accumulating evidence that many pedestal 

rocks, even in arid regions, are attributable primarily to other processes than wind erosion. The examples cited are due to processes 

which are also operative in humid regions. The fact that a relatively larger number are found in arid regions is probably due not 

so much to differences in the nature of the processes of weathering 

and erosion as in their rate, for in humid regions the formation of 

soil by chemical weathering and the growth of vegetation inhibit 

the formation of pedestal rocks in favorable places or rapidly destroy 

them when formed. 

33377° 27 3

CHANNEL EROSION OF THE RIO SALADO, SOCORRO 

COUNTY, NEW MEXICO

Deepening and widening of stream channels in the Southwest is 

a phenomenon that has taken place within the memory of men now 

living. It began at different dates from 1860 on and has progressed 

at different rates on several streams, as summarized in a recent 

paper.28 The flood plains of numerous minor streams are yet undissected, but nearly every one of them is menaced by a deep channel, 

or arroyo, which visibly increases headward each year. These 

channels, or arroyos, not only grow headward through the smooth 

flood plains of the valleys but constantly widen by lateral cutting 

and the growth of minor tributaries. It seems inevitable that the 

present flood plains will eventually disappear and new flood plains 

will form at lower levels.

The consequences of these processes to native life and to agriculture, stock raising, and other activities of man are numerous and 

important. Interesting scientific problems, are also raised. The 

various theories that have been advanced to account for this 

accelerated erosion are reviewed in the paper already cited.

Valid conclusions as to the merits of these theories can not be 

reached until historical data on the time at which erosion began 

have been accumulated. Knowledge of the date of the beginning 

and progress of this spectacular change in the regimen of streams 

is particularly necessary in arriving at a decision as to the effect 

on erosive processes of the introduction of cattle and sheep and the 

overgrazing that in most localities ensued. This paper presents, 

as a contribution to the necessary body of data, historical evidence, 

based on two reliable surveys made in 1882 and 1918, on the changes 

in the channel of a comparatively minor stream in New Mexico.

The Rio Salado, a tributary of the Rio Grande from the west, 

rises on the north side of the Datil Mountains and has a general

28 Bryan, Kirk, Date of channel trenching (arroyo cutting) in the arid Southwest: 

Science, new ser., vol. 62, pp. 338-344, 1925. See also Swift, T. T., Date of channel 

trenching in the Southwest: Idem, vol. 63, pp. 70-71, 1926; Wynn, Fred, The West Fork 

of Gila River: Idem, vol. 64, pp. 16-17, 1926.

17
18 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

eastward course north of that range and thence through a narrow 

gap between the Socorro Mountains and the Sierra Ladron to a 

junction with the Rio Grande at the village of San Acacia. The 

Rio Salado is formed by the junction of Alamosa Creek, also locally 

known as Rio Salado, and a large stream from the north. The total 

length of this drainage line, if Alamosa Creek is considered the 

main stem, is 75 miles, and the basin drained by it lies almost wholly 

in Socorro County. The village of Puertecito lies 2 miles above 

the junction of the two streams, and Santa Rita (Riley post office), 

7 miles below.

When Lorenzo Padilla, the first settler, who is still living at Santa 

Rita, came to the valley in 1880, the channel of the Rio Salado was 

inconsiderable, and the broad flat of the valley seemed a propitious 

place for farming. Consequently, others followed Padilla^ and 

according to the survey notes of Daniel Curry, who in 1882 subdivided the townships into sections, Santa Rita had by that time 

grown to a town of 100 inhabitants. Curry recorded the width of 

the stream bed as ranging from 11.88 to 48.84 feet on a number of 

section lines.

Because the town of Santa Rita lies in one of the odd-numbered 

sections which was granted to the Atlantic & Pacific Railroad and 

therefore belonged to its successor, the Santa Fe system, the inhabitants of the town had a defective title to the land. In support of an 

application by them to the United States General Land Office to have 

this land declared a public town site, Paul B. Moore, of Magdalena, 

N. Mex., was employed to make a survey. The information contained in this note was supplied by Mr. Moore, whose interest in New 

Mexican geology is large and whose help in this and other matters 

is hereby acknowledged. During this survey in 1918 he found the 

course of the river radically different from that shown in Curry's 

survey of 1882, his measurements ranging from 330 to 550 feet in the 

same stretch of stream channel where Curry found widths of 11.88 

to 48.84 feet. Some of these differences are tabulated below.

Width of Rio Salado at different points in T. 2 N., R. 4 W., 1882 and 1918

Location

14and23.-..--.._._........_....... ... ... ...... .....

U said 15. ...................................... ..............

16 and 16.......................-.......... ................

1882

Feet 

13.20

18.48

11.88

48.84

1918

Feet 

625.0

330.1

441.3

550.0

According to the testimony of the local inhabitants to Mr. Moore, 

there was an exceptional rain and flood in 1883, which washed out 

a road and formed a new stream channel. Since that time the chan-
CHANNEL EROSION OF THE RIO SALADO, NEW MEXICO 19

nel has constantly widened, and most of the agricultural land in 

the valley has been destroyed.

Unlike many similar streams in New Mexico, which have not only 

widened their channels but deepened them in the same period, the 

Rio Salado, at least in the vicinity of Santa Rita, has even yet banks 

that are only 3 to 10 feet high and average about 5 feet high. It is 

obvious, however, that the whole regimen of the stream is much 

different from that which existed in 1880.

But little is known of the progress of this erosion upstream. 

However, W. T. Thorn, jr., during a survey of the Alamosa Creek 

valley,29 witnessed, in August, 1923, headward erosion on Felipe 

Gilbert Creek, a tributary of Alamosa Creek. According to his 

notes, generously furnished for this paper, at a point in sec. 10, T. 

2 N., R. 7 W., 12 miles west-southwest of the village of Puertecito, 

the arroyo of this stream worked headward into the undissected 

valley flat a distance of 40 to 75 feet as a result of a single storm, 

destroying the road crossing and necessitating a detour by the party 

to avoid the steep-sided gully. From this record we may conclude 

that the progress of the erosion begun near Santa Rita in 1883 has 

been, as measured in years, fairly slow and has not yet, 43 years 

later, affected all the minor tributaries.

Thoughtful men must naturally consider whether it is possible 

to check such erosion and whether it would be profitable or otherwise 

advantageous to do so. One of the necessary items of information 

on which such a decision must be based is the relative value of the 

land in a dissected or undissected flood plain. Many writers have 

deplored the destruction of these valley bottoms, but no one has 

attempted to put a monetary value on the loss that has occurred, yet 

such an estimate is necessary before it is worth while to consider 

remedial measures.

29 Winchester, D. E., Geology of Alamosa Creek Valley, Socorro County, N. Mex., with 

special reference to the occurrence of oil and gas: U. S. Geol. Survey Bull. 716, pp. 

1-15, 1921.

THE "PALOUSE SOIL" PROBLEM

WITH AN ACCOUNT OF ELEPHANT REMAINS IN WIND-BORNE SOIL 

ON THE COLUMBIA PLATEAU OF WASHINGTON

By KIRK BRYAN

INTRODUCTION

Wheat is the great crop of eastern Washington. Grown on an 

extensive scale with all the ingenuity of modern labor-saving devices, 

it forms the basis for the stable prosperity of the " Inland Empire " 

which has its commercial center at Spokane. Deep, rich soil is the 

controlling factor in the growth of wheat in this area, for the rainfall is light, though advantageously concentrated in the winter season. The system of summer fallow is necessary to conserve the moisture of one season into the next, but thereby one-half the land lies 

plowed and idle. The wheat region, therefore, is a checkerboard of 

bare brown rectangles of plowed land alternating with rectangles of 

wheat that are green, gold, or buff according to the season.

The great Columbia Plateau, underlain except in a few small 

areas by basalt flows several hundred feet thick, has nearly everywhere a mantle of so-called soil, deep and retentive of moisture, the 

basis of this great wheat growing industry. This " soil" * is a finegrained mass that is intimately dissected into hills and valleys. (PI. 

4, A and B.) The little valleys are usually cut to or just below the 

level of the underlying basalt, so that the height of the hills, from 

100 to 150 feet, measures the thickness of this " soil." This material 

is locally known as " Palouse soil," from the rich wheat-growing area 

along Palouse Kiver south of Spokane, which is popularly known as 

the " Palouse country."

The Bureau of Soils, as shown in the summary of the history of 

the subject, on pages 22-26, recognizes in the region a number of soil 

series, only, one of which bears the name Palouse. All the names

1 The word soil is used throughout this paper in the ordinary sense both for the mantle 

of unconsolidated material overlying the hard rocks and for the upper part of this material, in which crops are grown, and not in the sense of ' solum " as defined by Frosterus 

(Frosterus, B., and Glinka, K., Zur Frage nach der Einteilung der Boden in nordwestEuropas Moranengebiet: Finland geol. Komm. geotek. Meddel. Nos. 11-14. 1914). See 

also Veatch, J. O., Geology as a factor in soil classification: Michigan Acad. Sci. Papers, 

vol. 5, pp. 287-296, 1926.

21
22 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

refer, as is the custom of the bureau, solely to the upper 6 feet or 

so of what is here called the " Palouse soil," although in places the 

material below is of exactly the same character. As this material 

is everywhere of about the same thickness and conforms to the slopes 

of the plateau, the assumption is justified that it once formed a continuous cover and has since been dissected. As it also has great 

extent and considerable thickness, it is a geologic body that would be 

worthy of a formation name if all parts of the mass were known to 

have had a common origin and age. Treasher 2 has recently proposed the name " Palouse formation," but, as is brought out in this 

paper, the common origin and age of the material is doubtful, and 

therefore it seems best to use the local term " Palouse soil" without 

implication that a formation name is being established.

Much remains to be learned about this widespread and economically important deposit, and the present paper is intended merely 

to outline briefly the current theories as to its origin, to present facts 

gained in the course of somewhat desultory field work, and to reconcile, so far as practicable, the known facts with the theories. The 

results may be summarized in the statement that the bulk of the 

" Palouse soil" is wind-borne dust or loess, though other material is 

included in its mass; that this loess is definitely of Pleistocene age, 

as shown by the occurrence of elephant remains in one of its later 

phases and by its association with glacial till; and that the present 

dust storms of the region are phenomena of the last few decades only 

and have contributed an inappreciable quantity of material to the 

Pleistocene loess.

The field observations here recorded were made as part of the 

geologic work done for the Federal investigation of the Columbia 

Basin irrigation project, conducted by the Bureau of Keclamation in 

1923, and were supplemented by a two-day visit to localities at and 

near Spokane in 1924. Data on dust storms, collected at the Spokane 

office of the United States Weather Bureau, have been put in tabular 

form, with the addition of rainfall data, by Mr. E. M. Keyser, whose 

generous cooperation is here* acknowledged. Mr. J. T. Pardee has 

contributed notes on his observations in the eastern part of the 

Columbia Plateau, and Mr. Clarence S. Ross has described samples 

collected by Mr. Pardee. Messrs. A. T. Strahorn and M. H. Lapham, of the United States Bureau of Soils, have read the manuscript 

critically and contributed valuable suggestions.

HISTORICAL REVIEW

The "[Palouse soil" has been of interest to geologists and soil 

scientists for many years, and its distribution and attributes can

1 Treasher, B. C., Origin of the loess of the Palouse region, Wash.: Science, new ser., 

vol. 61, p. 469, 1925.
THE "PALOUSE SOIL" PROBLEM ' 23

be best set forth in the course of a review of the numerous papers 

in which it is described and its origin considered.

Kussell,3 in his report on the eastern part of the Columbia Plateau, 

appears to have been the first to describe the characteristics of the 

" Palouse soil" and discuss its probable mode of origin. He believed that the "soil" was primarily due to the decay of the underlying 

basalt, but that it had, after the devlopment of the present intricate 

drainage pattern, been reworked superficially by wind an agent 

that had also slightly modified the form of some of the hills. These 

conclusions he supported by evidence obtained four years later from 

the adjacent region in Idaho.4 Calkins,5 after a reconnaissance of 

the western part of the plateau, contended that the " soil" was deposited by wind and that the material was not derived from the 

underlying basalt but from water-laid deposits on the southwestern 

margin of the plateau. He held, hoAvever, that the " soil" was once 

a continuous layer and has been since dissected.

Since these papers were written several soil surveys have been 

made in the region by the United States Bureau of Soils. In 

Franklin County, in the western part of the plateau, the Kitzville 

series of soils was recognized in 1914.6 Of this series the silt loam 

is the most widely distributed and is described as a light-brown 

compact silt loam of a uniform texture to a depth of 6 feet or 

more. The underlying material is of similar character and extends 

to basalt bedrock at depths of 50 to 100 feet. Mechanical analyses 

show that. 50 per cent is silt and only 2 to 4 per cent clay. One of 

the samples was examined for its constituent minerals and found to 

contain orthoclase, quartz, biotite, hornblende, plagioclase, and traces 

of isotropic materials of low refractive index. In 1916 the Kitzville 

series, was found also in Benton County, west of Columbia Kiver, 

and here it forms the surface of a large part of Horseheaven Plateau.7 

Farther east, however, in the Palouse region, darker soils form the 

surface. In this region the Palouse series was recognized, and the 

name Palouse appears to have been first used for a soil series as a 

result of the survey of Latah County, Idaho, in 1915.8

The Palouse silt loam, as described in the report cited, consists of 

8 to 14 inches of dull-brown or dark-brown silt loam lying on

3 Russell, I. C., A reconnaissance In southeastern Washington: U. S. Geol. Survey 

Water-Supply Paper 4, pp. 57-69, 1897.

* Russell, I. C., Geology and water resources of Nez Perce County, Idaho: U. S. Geol. 

Survey Water-Supply Paper 53, pp. 81-83, 1901.

6 Calkins, F. C., Geology and water resources of a portion of east-central Washington: 

U. S. Geol. Survey Water-Supply Paper 118, pp. 44-49, 1905.

6 Van JDuyne, Cornelius, and others', Soil survey of Franklin County, Wash.: U. S. 

Dept. Agr. Bur. Soils Field Operations for 1914, pp. 45 et seq., 1917.

7 Kocher, A. E., and Strahorn, A. T., Soil survey of Benton County, Wash.: U. S. Dept. 

Agr. Bur. Soils Field Operations for 1916, pp. 26-32, 1919.

8 Agee, J. H., and others, Soil survey of Latah. County,. Idaho: U. S. Dept Agr. Bur. 

Soils Field Operations for 1915, pp. 14, 17-18, 1917.
24 CONTRIBUTIONS TO GEOGEAPHY OF UNITED STATES, 1926

brownish-yellow or light-brown silt loam which extends to a depth 

of 36 to 40 inches and which in turn rests on a tawny-yellow substratum of homogeneous and unstratified material that has a thickness of 50 feet or more and rests on the basalt bedrock. The 

substratum is considered to be of loessial origin and to be the source 

of the agricultural soil. The Helmer series of soils in the same area 

are also thought to be of wind-borne origin, but these soils have a 

thickness of 2 to 5 feet only and rest on decomposed granite.

As a result of the soil survey of Spokane County, Wash., somewhat 

more diverse materials were included under the term Palouse series.9 

Four soil types are described.

The Palouse sandy loam is 1 to 5 feet thick and overlies a finegrained subsoil derived from the weathering of granite.

The Palouse fine sandy loam consists of 8 inches of friable darkbrown fine sandy loam with a subsoil about 3 feet thick of loose 

light-brown to yellowish-brown sandy loam. The subsoil is underlain by material of similar color and texture about 10 feet thick that 

rests on basalt. This substratum is derived from lake deposits or 

glacial till.

The Palouse loam is a dark-brown loam, 10 inches thick, with a 

subsoil of brownish-yellow fine sandy loam 10 feet or more thick. 

The subsoil rests on a very compact reddish-brown material similar 

to the substratum of the Palouse silt loam next to be described. 

Granitic and basaltic boulders, some of which bear glacial striae, 

occur on the surface and in the soil.

The Palouse silt loam consists of 10 inches of dark grayish-brown 

friable silt loam with a subsoil of yellowish-brown to brown heavy 

silt loam or silty clay loam 3 feet thick. Below the subsoil is a 

substratum of unstratified compact reddish material about 50 feet 

thick that lies on basalt but in places overlaps on granite and schist. 

In these places the residual character of the substratum is evident.

In their general sections the authors of the report cited 10 take the 

stand that the Palouse soil series, particularly the Palouse silt loam, 

is derived from the mantle of fine-grained material overlying the 

basalt and that this material is of wind-borne origin. They consider that there is no gradation through decomposed to unaltered 

rock* except where the material rests on granite and schist. The dissection of the "soil" mantle is ascribed to stream erosion during 

some previous period, but in places the hills are thought to be modified by wind action so as to give steep northern and more gentle 

southern slopes. Except in the matter of the residual character of 

the substratum, these authors are in accord with Kussell. They

8 Van Duyne, Cornelius, and others. Soil survey of Spokane County, Wash.: U. S. Dept. 

Agr. Bur. Soils Field Operations for 1917, pp. 35 et seq., 1920. 

"Idem, p. 35,
THE * PALOUSE SOIL" PROBLEM 25

note the widespread superficial redistribution of soil material during 

dust storms, with evidence of some accessions from outside sources, 

and the tendency for calcium carbonate to accumulate in the soil 

below the surface. They make the first published statement that 

much of the " soil" mantle accumulated prior to the last glacial invasion.

In the soil survey of Nez Perce and Lewis Counties, Idaho,11 three 

series of residual soils were distinguished, of which two, the Tolo and 

Waha series, are derived from basalt. Both are thin soils, and the 

Waha, 20 to 30 inches thick, occupies slopes below the flat summits 

of plateaus overlain by " Palouse soil." Three loessial soils are distinguished the Palouse, Nez Perce, and Southwick. The Palouse 

soil series here is much like that in other areas. The Nez Perce and 

Southwick are less than 15 feet thick but except for difference in 

color are very like the Palouse.

In Kootenai County, Idaho,12 in addition to the Palouse soil series, a loessial series known as the Helmer is distinguished. It was 

originally forested and for a depth of 10 inches below its surface 

is much lighter in color than the typical Palouse silt loam. Generally there are four distinct layers differing in color in the first three 

feet. The Helmer soil attains a thickness of 50 feet and overlies 

basalt.

It is evident from the foregoing review that there are large differences in the " soil" mantle of the Columbia Plateau, which seems 

at first glance so homogeneous and characteristic. In the upper 3 

feet the soil is universally fine grained and is generally a silt loam or 

loam. There is, however, a gradation in color from tawny yellow 

in the western part of the plateau to dark brown in the Palouse 

country and even an ashy gray farther east in Idaho. This change is 

largely due to change in humus content coincident with increased 

rainfall and heavier natural vegetation in the eastern part of the 

plateau. The principal differences noted are in the substratum below the upper 3 feet. In the succeeding sections some of these differences are further considered.

Bretz 13 describes the " soil" in general terms and brings forward 

physiographic evidence to show that the main body of the material 

is older than the stage of ice advance preceding the Wisconsin, to 

which he has given the name " Spokane." He also notes that the loessial soil near Cheney rests in places on glacial till, which he suggests

u Agee, J. H. and Peterson, P. P., Soil survey of Nez Perce and Lewis Counties, 

Idaho: U. S. Dept. Agr. Bur. Soils Field Operations for 1917, pp. 18 et seq., 1920.

ia Lewis, H. G., and Denecke, W. A., jr., Soil survey of Kootenai County, Idaho: U. S. 

Dept. Agr. Bur. Soils Field Operations for 1919, pp. 35 et seq., 1923.

13 Bretz, J, H., Glacial drainage on the Columbia Plateau : Geol. Soc. America Bull., 

vol. 84, pp. 673-608, especially p. 577, and footnote pp. 588 and 589, 1923: The channeled scablands of the Columbia Plateau: Jour. Geology, vol. 31, pp. 623-634, 1923.
26

may belong to a still older glaciation. This observation is confirmed 

by Freeman,138- who reports the finding near Cheney of elephant 

bones in "loess" overlying well-weathered till attributed to this 

early glaciation. It is obvious from Bretz's work, as supported by 

evidence in the present paper, that there are at least three bodies 

of glacial till in this area, representing as many glacial advances. 

In this paper the terms early, intermediate, and Wisconsin are applied to these bodies of till and corresponding glacial stages.

Kecently MacMacken 14 has given a general popular treatment of 

the problem, and Treasher,15 in a short note, advocates the hypothesis 

of accumulation of an original laminated silt in ephemeral sheets of 

glacial water as "water-laid loess," and later rehandling of this 

material by wind.

Short notes by Peterson 16 and by Larsen 17 record the present 

accumulation of dust in the region and regard the " soil" as a loess 

still in process of formation.

OBSERVATIONS

In general, only the upper part of the " Palouse soil " can be seen. 

This surface portion is a tawny brown in the western part of the 

plateau and a deep brown, almost black, in the Palouse country and 

farther east in Idaho. The names Kitzville, for the Franklin County 

area, and Palouse, for the Spokane County and Idaho areas, used by 

the Bureau of Soils, carry a valid distinction. In the western part 

of the Columbia Plateau numerous contacts on undecomposed though 

not wholly fresh basalt can be found, and all of Calkins's observations 

of fact confirmed. However, in a cut on the new State highway 

from Lind to Connell, in the SE. % sec. 20, T. 14 N., K. 32 E., about 

2 miles north of Connell, finely laminated gray-brown silt is exposed. 

This material forms the core of the hill, and the exposed portion has 

a thickness of about 10 feet. The usual loesslike soil mantles the silt 

in a layer about 5 feet thick that conforms to the shape of the hill. 

The silt is evidently water-laid and resembles beds near the top of 

the Kingold formation as exposed in the White Bluffs northeast of 

Pasco and at other localities. Whatever its origin, the silt is an ideal 

formation from which the upper soil might have been derived by

18a Freeman, 0. W., Mammoth, found in loess of Washington: Science, new ser., vol. 

64, p. 477, 1926.

14 MacMacken, J. G., Eolative soils of Washington wheat lands: Pan-Am. Geologist, 

vol. 43, pp. 177-184, 1925.

16 Treasher, R. C., Origin of the loess of the Palouse region, Wash.: Science, new ser., 

vol. 61, p. 469, 1925.

"Peterson, P. P., Rate and mode of soil deposition in Palouse area of Washington 

and Idaho: Science, new ser., vol. 55, pp. 102-103, 1922.

17 Larsen, J. A., Soil shifting and deposits: Science, new ser., vol. 55, p. 457, 1922; 

Dust storms of northern' Idaho and western Montana: Monthly Weather Review, vol. 

52, p. 110, 1924.
THE "PALOUSE SOIL" PROBLEM 27

redistribution through the agency of wind, provided that it were 

favorably exposed and free of vegetation.

Loesslike soil not only occurs on the broad surfaces of the Columbia Plateau, but similar material of a younger stage lies on the terraces that are typical of certain canyons cut into the plateau surface. 

The gulch known as Old Maid Coulee, 5 miles south of Connell, has 

a southwesterly course across the plateau (PI. 4, (7), and receives 

numerous tributaries proportioned in size to their length, which 

with the main gulch form a dendritic pattern. Old Maid Coulee 

seems, therefore, to be a normal stream valley and to be sharply 

distinguished from Esquatzel Coulee, to which it is tributary. 

Esquatzel Coulee belongs to the group that were deepened and modified by the great streams diverted across the plateau during glacial 

time, whereas Old Maid Coulee was developed by normal erosion 

before the diversion of the glacial waters that formed Esquatzel 

Coulee. Old Maid Coulee has a well-marked but discontinuous terrace rising about 50 feet above the floor of the gulch. This terrace 

is floored by coarse, fairly well waterworn gravel, evidently deposited 

by a shifting but not necessarily turbulent stream. The gravel is well 

exposed in a pit opened on the west side of the State highway in the 

NE. 14 sec. 14, T. 13 K, R. 31 E. Here, as shown in Plate 5, A, the 

gravel is overlain by soil that is indistinguishable from the rest of 

the "Palouse soil." This soil ranges in thickness from 2 feet near 

the margin of the terrace to 12 feet or more at the back end of the 

pit. About 18 inches above the gravel there is a well-marked zone 

of calcareous nodules about 2 feet thick. It seems evident that the 

soil has accumulated on the terrace by local redistribution of the 

previously formed soils that rest on the undissected plateau surface 

above. Slump, soil creep, rain wash, and wind have doubtless all 

played parts in this process. Similar gravel terraces with like soil 

coverings were observed in Rattlesnake Coulee and in Smith Canyon.

The larger coulees of the plateau are of two types those which 

resemble normal stream valleys and those which were evidently cut 

by the headward erosion of large rivers. Of the first group Lind 

Coulee, Third Coulee, and the upper part of Black Rock Coulee 

have rather smooth slopes of partly weathered basalt more or less 

covered with soil that seems to have accumulated in a manner 

similar to that on the terraces of Old Maid Coulee. The coulees of 

the second type have bold and ragged walls of nearly fresh basalt, 

yet even here there are scattered small areas of soil evidently due 

to redistribution by wind of the original soil of the plateau. 

Washtucna and Esquatzel Coulees, which are typical of this group,

18 Brelz, J. H., Glacial drainage on the Columbia Plateau: Geol. Soc. America Bull., 

vol. 34, p. 587, 1923.
28 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

were cut by glacial waters, although, as Bretz 18 has pointed out, 

they were probably formed during the .intermediate and not the 

latest stage of glaciation.

Over the general plateau surface the depth of the soil is known 

only from rather unsatisfactory well records, and the lower part 

is rarely exposed. Generally, as observed by Strahorn,19 there is 

below a depth of 3 feet a limy layer in which the soil is firmly 

cemented and contains seams, threads, and nodules of calcium carbonate. The upper 3 feet of soil mapped by Strahorn as Ritzville, 

whether belonging to the main mass or to the terrace, contains so 

little lime that it will not react with acids.

In this western part of the plateau the main body of the " Palouse 

soil" is exposed in only a few places, being generally covered by 

a veneer of wind-borne material, but similar material occurs also 

on the terraces and in small bodies on the coulee walls. This windborne material has been formed in at least five ways in one or all 

of as many different stages (a) formed from the substratum or 

forming the substratum before the small valleys were cut; (b) 

formed by redistribution by wind and also by soil creep during 

and after the period of formation of the terraces in gulches of 

the Old Maid Coulee type; (c) formed by wind distribution on the 

rocky slopes of coulees cut during the intermediate or some earlier 

stage of pre-Wisconsin glaciation or perhaps during more than one 

such stage; (d) formed by wind distribution during the Wisconsin 

stage of glaciation; (e) formed by redistribution of previously deposited material with possible additions of foreign material since 

Wisconsin time.

- In the eastern part of the plateau there is the same upper skin or 

veneer of soil over a more compact substratum. As described in 

the soil reports, the upper 6 inches is dark, and the subsoil in general 

is light in color. The thickness of the veneer is doubtless variable, 

and only a few road cuts show the underlying substratum. The opportunities of the writer to make observations in the area have been 

so meager that only a few details can be given, which are, however, 

supplemented by observations and collections made by Mr. J. T. 

Pardee.

West of the railroad station of Fishtrap a road cut exposes the 

veneer of soil and the substratum as shown in Plate 5, B. The humus 

layer is dark brown, and the subsoil below it is tawny yellow. Both 

are fine-grained silts and have an inconspicuous vertical structure. 

That both these layers are composed of wind-borne dust seems probable. They rest unconformably on the substratum and form a shell 

corresponding to the slopes of the hill, and thus, before the road 

cut was made, they completely hid the substratum. The substratum

10 Strahorn, A. T., letter dated November 4, 1925.
THE '' PALOUSE SOIL '' PROBLEM 29

is a light brick-red or pink mass without stratification, composed of 

material as fine as the overlying soil. It is more compact and has 

an obscure horizontal structure that is like an imperfect shale parting. Calcareous nodules from 1 to 3 inches in diameter are scattered 

through the mass and are visible in Plate 5, B, as white spots. The 

contact of this material with the basalt is not exposed.

A number of road cuts near and south of Rosalia show a somewhat 

similar substratum, but the contacts with the veneer above and the 

basalt below are obscure. The extent of this reddish substratum 

is not known, but it corresponds to the substratum of the Palouse silt 

loam as described in the soil survey of Spokane County (see p. 24) 

and doubtless has a considerable areal extent. The origin of this 

material is also uncertain, but from its general appearance there 

seems to be no good reason why it can not be interpreted as an old 

loess once similar to the overlying soil but more compacted and 

oxidized. Except for the lime nodules, it is similar to the tawnyyellow clay at localities a few miles distant described below by Mr. 

Pardee.

Treasher 20 reports laminated water-laid silts in the substratum 

from this general area. Russell,21 in places in this eastern part of 

the plateau, found complete transitions between basalt, decomposed 

basalt, and the top soil. On the other hand, J. T. Pardee, in October, 

1922, collected a suite of samples that indicates that the different 

layers of the soil are distinct from the decomposed basalt and are 

partly at least of distant origin. The following description of the 

specimens is furnished by Mr. Pardee:

Decomposed, basalt. At a quarry 2 miles north of Plaza soft greenish-gray 

to lead-gray material that shows the texture and jointing of basalt is exposed 

to a depth of 15 feet. No fresh rock is visible in the quarry face, but spheroidal 

cores of hard black basalt can be broken out of the joint blocks, which are 6 

inches or more thick. A heap of these cores which had been divested of their 

decomposed shells by means of a rock crusher looked not unlike so many cannon 

balls of different sizes. The altered shell shows concentric rings or zones which 

mark steps in the progress of the weathering and the change of rectangular 

blocks into spheroids. The altered material is lightly spotted and streaked with 

iron and manganese oxides, and it contains numerous small bodies of a yellowish-green, apparently noncrystalline substance which W. T. Schaller has identified as an iron-bearing silicate of the chlor-opal group, probably nontronite. 

There is no gradation between fresh rock and altered rock, the change from 

one to the other being sharp and abrupt.

In the lower part of the quarry face several seams and joints are filled with 

a reddish-brown material that ranges in composition from an iron-rich clay to 

limonite (hydrated iron oxide). The occurrence of this material suggests that 

the decomposition of the basalt was accompanied by the solution and removal 

of some of the iron. The decomposed basalt is overlain by a few feet of soil 

that appears nowise different from the top soils that occur in the general area.

20 Treasher, R. C., op. cit., p. 469.

21 Russell, I. C., op. cit., pp. 59-63.
30 CONTRIBUTIONS TO GEOGEAPHY OF UNITED STATES, 1926

A quarry west of St. John shows altered basalt like that just described, 

underlain by undecomposed basalt, the two being separated by a thin layer 

composed of iron oxides. Apparently this layer is at the parting between two 

flows. Above the altered basalt is a layer of clay mixed with basalt fragments, 

apparently an old surface mantle, and above this is several feet of typical 

"Palouse soil."

On the plateau just beyond the end of the long grade north of Colfax a road 

cut exposes 6 feet of altered basalt that shows the characteristic gray shades, 

vesicular texture, streaks and spots of iron oxides, and bodies of the green 

mineral. Here the decomposition is complete, no unaltered cores remaining. 

Obviously this material, which now can be cut with the finger nail, was once 

hard basalt, a conclusion that is confirmed by the microscopic examination 

made by C. S. Ross of a representative sample (specimen 78) as described on 

page 31 and illustrated in Plate 6, A.

From the foregoing statements it appears that in the region north and west 

of Colfax the basalt at some former time has been rather deeply weathered, 

but that locally at least the residual product is quite distinct from the " Palouse 

soil." Furthermore, so far as observed, this material is apparently absent in 

places and where present is of comparatively small bulk and ordinarily would 

be classified as part of the basalt formation.

"Palouse soil." Road cuts at the upper end of the long grade north of 

Colfax expose 20 feet or more of the typical buff, tawny, or brownish-yellow 

clay (pi. 6, B), overlain by the typical dark surface soil. Near the top of the 

grade this material rests on a gently sloping surface of partly decomposed 

basalt. The separation between the two is distinct, and the clay was apparently deposited after the basalt had been somewhat cut away by erosion. At 

this locality the clay is fine and rather tough, with closely spaced vertical 

joints and numerous small tubelike cavities and irregular vesicles. So far 

as their vesicular texture is concerned some specimens of the clay are difficult 

to distinguish from the decomposed basalt; their color, however, is different 

and they lack the characteristic greenish substance.

In a road cut on the Inland Empire Highway 3 miles south of Spangle 

specimens were collected representing 16 feet or more of typical " Palouse soil." 

The section exposed is made up of the following beds:

Section in road cut 3 miles south of Spangle

Feet

1. Top soil of light-brownish or reddish-yellow color, loosely 

compacted and showing an indistinct wavy lamination 

(pi. 6, C) ___________________________ 3-8

2. Dark-gray, almost black subsoil, rather firm and tough,

laminated like No. 1_____________________ 2

3. Reddish-brown tough claylike layer exhibiting vertical

joints 2 or 3 inches apart; grades downward into No. 4_ 3

4. Brownish-yellow to buff rather compact clay, but not so 

hard or so tough as No. 3. Contains a few small concretions cemented with manganese and iron oxides, and 

with the aid of a hand lens many fine specks that look 

like scales of a colorless mica can be seen __ 8+ 

Bottom not exposed.

Specimens 65 to 68 represent, respectively, layers 1 to 4 in the above section. 

Specimens 77 and 77a represent the " Palouse soil" exposed at the top of the 

long grade north of Colfax, and specimen 78 represents the decomposed basalt 

in the road cut a little farther north,
THE " PALOUSE SOIL," PROBLEM 31

As a result of petrologic studies of some of the samples from the 

exposures described above, Mr. Clarence S. lioss has prepared the 

following statement:

Thin sections that preserved the original structure were made from the specimens collected by Mr. Pardee by the use of a relatively new hardening process 

in preparing sections for microscopic study.22 By ordinary washing the larger 

grains were freed from clay, and the individual minerals were identified by the 

method of obtaining the index of refraction through immersion in liquids 

whose index is known.

Specimen 78, of the Colfax suite, is an altered basalt that retains without 

change the vesicular and mineral structure of the original rock, as easily seen 

In the photomicrograph, Plate 6, A. Plagioclase, augite, and olivine are all 

recognizable, but the plagioclase has altered to a very fine grained aggregate 

of kaolin-like minerals, and augite and olivine have been changed to a material 

resembling serpentine.

Specimens 67 and 08, of the Spangle suite, and 77 and 77a, of the Colfax 

suite,- are similar to each other and are composed of fine siltlike material of 

a yellow-buff color, consisting of angular mineral grains embedded in a brown 

clayey material. This material has the characteristics of substances that 

crystallize from gel-like colloids (rnetacolloidal habit) and possesses optical 

properties that indicate it to be an iron-bearing beidellite.23 Most of the grains 

embedded in the beidellite range from 0.01 to 0.05 millimeter in diameter, but 

a few measure 0.1 millimeter. They consist predominantly of quartz, but orthoclase, plagioclase, rnuscovite, biotite, and green hornblende are not rare. 

Less abundant are brown hornblende, garnet, tourmaline, apatite, and zircon. 

The texture of these specimens is well shown in Plate 6, B.

Specimens Nos. 65 and 66, of the Spangle suite, are alike in mineral composition and differ from each other in color only. No. 65 is brownish gray, and No. 

(36 is dark brown, and both contain much more organic material, to which the 

color is due, than specimens 67, 68, 77, and 77a. The grains are angular and 

are embedded in brown clayey material and beidellite. About 90 per cent of 

Ihe grains range in diameter from 0.01 to 0.05 millimeter and consist of quartz, 

orthoclase, plagioclase, hornblende, biotite, muscovite, garnet, zircon,, and 

apatite. That is, the bulk of the grains and the inclosing grouudmass are identical in habit, origin, and mode of deposition with the material represented in 

specimens 67, 68, 77, and 77a.

However, a small part of the grains, estimated as 5 to 10 per cent of the 

total, are about 10 times the ordinary size and range from 0.1 to 0.3 millimeter in diameter. They consist of andesine having about the composition 

of AbooAn«, brownish-green hornblende, augite, and magnetite. Quartz 

grains of this size are entirely absent. These grains, as may be seen in Plate 

6, C, are predominantly euhedral in outline, and the feldspar is strongly zoned.

The characteristic material of the tawny-yellow clay and the predominant 

material in the dark upper soils, as represented by these specimens, is fine 

grained, .angular, and rather evenly sorted. Its composition indicates that 

it is not derived from the underlying basalt or decomposed residual material 

but is made up of minerals of diverse origin, some of which are characteristic

22 Ross, C. S., A method of preparing thin sections of friable rock: Am. Jour. Sci.. 

5th ser., vol. 7, pp. 483-485, 1924; Methods of preparation of sedimentary material for 

study: Econ. Geology, vol. 21, pp. 454-468, 1926.

23 Larsen, E. S., and Wherry, E. T., Beidollitc, a new mineral name: Washington Acad. 

Sci. Jour., vol. 15, pp. 465-4CG, 1925. Ross, C. S., and Shannon, E. V., The chemical 

composition and optical properties of beidellite: Idem, pp. 46.7-468.
32 CONTRIBUTIONS TO GEOGRAPHY OP tJtflTED STATES, 1926

of silicic igneous and metamorpkic rocks. All tkis indicates ratker clearly tkat 

tke material was deposited by tke wind. The metacolloidal kabit of tke 

clayey material skows tkat muck of it was formed by tke breaking down, 

after decomposition of tke mass, of-unstable minerals of unknown origin into a 

colloidal material wkick was later crystallized into beidellite.

Tke two groups of minerals in specimens 65 and 66 are in mineral composition entirely distinct, and no grains transitional in size were present. Tke 

smaller grains consist of angular fragments, predominantly of quartz and in 

less degree of ortkoclase, and differ not at all from tke grains of tke tawnyyellow clay specimens. Tke larger grains contain no quartz and no ortkoclase 

but consist of andesine, kornblende, augite, and magnetite tkat are strikingly 

eukedral. Tkese grains kave all tke ckaracteristics of pkenocrysts derived 

from volcanic rocks of andesitic composition. Tkeir lack of rounding and 

retention of crystal form indicate tkat tkey came to place witkout wear and 

doubtless were deposited directly from tke air. Tkey probably were never 

deposited elsewkere but settled kere as tke result of a skower of volcanic 

dust from a distant source.

Specimens 67, 68, 77, ^and 77a may contain a little volcanic material, but 

if present it is far less abundant tkan in specimens 65 and 66, and tkere is 

no marked difference in size between tke crystals and crystal fragments of suck 

origin and tke otker wind-blown grains, by wkick a discrimination between 

tke two classes can be made.

A sample typical of tke well-known loess at Council Bluffs, Iowa, was supplied by W. C. Alden and subjected to tke same analysis. As well skown in 

Plate 6, C, tkis material kas grains similar in size, freskness, and angularity 

to tkose of tke tawny-yellow loess from Spangle and Colfax, altkougk differing 

in mineral ckaracter. So far as tkese observations are critical, tke features of 

tke admitted loess from Iowa confirm tke opinion given above as to tke 

origin of tke " Palouse soil" samples.

These observations and studies indicate that the close resemblance 

between the clayey lower part of the " Palouse soil " and the decomposed basalt, which in places in the eastern part of the Columbia 

Plateau, as at Colfax, underlies the " soil," is wholly superficial. The 

extent to which this yellow clay forms the lower part of the " Palouse soil" was not determined, but according to the observations of 

Mr. Pardee, it is present throughout a considerable area. The description of the substratum of the Palouse silt loam in the soil survey 

of Latah County indicates that it extends into Idaho (p. 23). In the 

localities described by Mr. Pardee the tawny-yellow soil is composed 

of mineral grains that originate in granitic, gneissic, and metamorphic rocks. The nearest outcrop of such rocks is in the encircling 

mountains to the north and east, yet the prevailing winds come from 

the west and south, as perhaps did also those of Pleistocene time. 

The coarsest eolian soil (Ritzville type), which as indicated on 

page 23 has a somewhat similar mineral composition, blankets the 

plateau to the southwest in the direction of the prevailing winds. 

It seems possible only to suggest that this material was carried from 

the mountains in the channels of the ancestral Snake and Columbia 

Rivers and has since been returned from the vicinity of their junction
THE f ' PALOUSE SOIL '' PROBLEM 33

by wind action. Understanding of the details of the processes by 

which this transfer was accomplished, however, awaits fuller 

knowledge of the sequence and character of Pleistocene events in 

this region.

The discovery by Mr. Eoss of volcanic debris in the upper darkcolored layers suggests the possibility that correlation of soil layers 

from place to place on the basis of a content of volcanic dust may 

eventually be possible. That volcanic explosions have occurred in 

this general region in very late geologic time has long been recognized. Russell 24 has described a deposit of volcanic dust that lies 

in sheltered places in Latah County, Idaho, and must be due to recent 

dust showers. A deposit of volcanic dust of very late date occurs 

in Oregon.25 It has been largely washed from the hillsides and now 

lies in the valleys and in small alluvial fans at the mouths of gulches, 

where it is from 1 to 10 feet deep. To the southwest, near Umatilla, 

Oreg., Hewett 26 has found a similar deposit of very late though 

prehistoric date.

In the soil survey of Spokane County already mentioned the 

loesslike upper soil was observed overlying a substratum of reddish 

material similar to that observed by the writer at Fishtrap, but there 

is no reason to believe that this reddish substratum is essentially 

different from the yellow clay found by Mr. Pardee in the same 

region.

The Bureau of Soils, however, recognized below the top skin of 

loessial soil a substratum made up of glacial till and even of decomposed crystalline rock, although in these localities the total thickness of unconsolidated material is generally less than 20 feet. Freeman 20a has confirmed this observation by finding " loess " overlying 

ancient till near Cheney.

On Pleasant Prairie, in areas covered by soils of the Palouse series, 

as mapped by the Bureau of Soils, a fine gray to light-brown soil 18 

inches to 3 feet thick lies above a compact and somewhat decomposed 

glacial till. (PL 7, C.) This till is distinguished by its state of 

weathering and position from that of the intermediate glacial stage 

as observed by the Avriter and described by Bretz.27 (See also p. 42.)

It is evident from the foregoing statements that the so-called 

" Palouse soil " in many localities consists of a relatively thin veneer 

over a substratum of unconsolidated material that makes up the

24 Russell, I. C., Geology and water resources of Nez Perce County, Idaho: U. S. Geol. 

Survey Water-Supply Paper 53, pp. 33-34, 1901.

25 Pardee, J. T., and Hewett, D. F., Geology and mineral resources of the Sumter 

quadrangle, Oreg.: Oregon Bur. Mines Mineral Resources, vol. 1, No. 6, p. 17, 1914. 

Grant, U. S., and Cady, G. II., Preliminary report on the general and economic geology 

of the Baker district of eastern Oregon : Idem, pp. 143-144.

20 Hewett, D. F., personal communication.

so,. Freeman, 0. W., op. cit, p. 477.

27 Bretz, J. I-L, Glacial drainage on the Columbia Plateau: Geol. Soc. America Bull., 

Vol. 34, p. 580, 1923.
34 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

larger part of the core of the intricate maze of hills and ridges characteristic of the areas in which the " soil" occurs. The upper soil, 

which is from 3 to 10 feet deep, is wind-borne material, as admitted 

by all writers on the subject. Though part of it may have arisen 

from a superficial reworking of the underlying material by wind, as 

Russell suggested, the work of Mr. Ross shows that in places it contains mineral grains from distant volcanic explosions. The establishment of this fact leads to the inference that other parts not discriminated also had a distant source.

The underlying material is to be seen only in artificial exposures. 

Many of these are road cuts on the flanks of hills, where the veneer 

is thick. In the western part of the plateau some of these cuts, if 

not all, lie in the more recent soil corresponding to that which overlies the terrace in Old Maid Coulee. As suggested on page 37, the 

fossil elephant bones described in the next section probably occur in 

soil of this kind. Thus the underlying materials composing the substratum have been exposed in only a few places, and here they are 

of one or more of three kinds a stratified and obviously waterlaid silt, a compact unstratified reddish or yellow silt or clay, perhaps 

wind-borne, and an ancient glacial till. The observations of Mr. 

Pardee and the studies of Mr. Ross indicate that possibly none of the 

true substratum is residual from basalt. That these different materials were contemporaneous in their accumulation seems unlikely, as 

the period of time in which they may have accumulated extended 

from the last outpouring of basalt in Miocene time 28 to some part of 

the Pleistocene epoch. The patches of decomposed basalt that in 

places underlie the " Palouse soil " required time for their formation, 

and this fact shortens to some extent the time available for the deposition of the " Palouse soil."

6

DISCOVERY OF FOSSIL BONES

While making an inspection of the soil survey of the Columbia 

Basin irrigation project A. T. Strahorn, in charge of the soil survey, 

E. J. Carpenter, soil scientist, and M. H. Lapham, western inspector, 

all of the United States Bureau of Soils, found, on September 12, 

1923, fragments of large bones and the jaws and skulls of rodents 

in a road cut in Franklin County. The writer was summoned from 

Spokane by long-distance telephone, and on the 13th, with the 

assistance of these gentlemen and Prof. F. J. Sievers, began excavations. On the following four days the writer, with a local helper, 

continued the work and recovered about 800 pounds of fossil bones.

28 For recent data on the age of the basalt flows, see Pardee, J. T., and Bryan, Kirk, 

Geology of the Latah formation in relation to the lavas of the Columbia Plateau near 

Spokane, Wash.: U. S. Geol. Survey Prof. Paper 140, pp. 1-16, 1025.
U. S. GEOLOGICAL SURVEY BULLETIN 790 PLATE 4

A. HILLS OF "PALOUSE SOIL" RISING ABOVE THE SGABLAND NEAK HILLCREST, WASH.

The lower 50 feet of these hills is basalt, generally masked by slump of soil from above. 

Photographed in 1923

S. ROLLING TOPOGRAPHY OF A "PALOUSE SOIL" AREA IN WHITMAN

COUNTY, WASH.

Photographed by J. T. 1'ardee, 1923

C. ROLLING TOPOGRAPHY AT OLD MAID COULEE, WASH.

The "Palouse soil" is 75 feet thick on the upland, but a mantle of similar though younger 

material covers the slopes and terraces of the valley. Photographed in 1923
r. S. GEOLOGICAL SURVEY BULLETIN 790 PLATE o

A. GRAVEL PIT IN THE TKRRACE ON OLD MAID COULEE, WASH. 

Exposing well-rounded stream gravel overlain by fine-grained loess. Photographed in 1923

75. ROAD CUT AT FISHTHAP, WASH.

Showing veneer of loess overlying reddish compact fine-grained material that may be old 

loess. Photographed in 1923
U. S. GEOLOGICAL STTRVEY BULLETIN 790 PLATE 6

PHOTOMICROGRAPHS ILLUSTRATING CHARACTERISTICS OF SOIL RESIDUAL 

FROM RASALT, SUPPOSED LOESS, AND LOESS

A, Decomposed basalt from road cut north of Coif ax, Wash., specimen 78; 7?, typical tawnyyellow clay of the lower part of the " Palouse soil " from road cut north of Colfax, Wash., 

specimen 77; O, typical brownish upper layer of the "Palouse soil" from road cut south 

of Spangle, Wash., specimen 65; D, loess from Council Bluffs, Iowa. 'All enlarged 105 

diairicters
U. S. GEOLOGICAL SURVEY BULLETIN 790 PLATE

A. LOWER JAW OF ELEPHAS COLUMBI FROM WIND-UORNE SOIL ON THE 

COLUMBIA PLATEAU, WASH.

S. ROLLING HILLS OF COLUMBIA PLATEAU AT ELEPHANT LOCALITY, 

15 MILES SOUTHWEST OF KAHLOTUS, WASH.

Photographed in 1923

l^^^^^^^^^^^^^jj^^^^'_^__ PT* ^^^Wii wi^^Bp^^wip ,^^*^^^

C. HOAD CUT ON PLEASANT PRAIRIE, NORTH OF SPOKANE, WASH. 

Showing loess overlying compact glacial till of the early glaciatiou. Photographed iu 1924
THE "PALOUSE SOIL" PEOBLEM 35

The bones were found in two adjacent road cuts on the PascoKahlotus highway, in the SW. % sec. 27, T. 12 N., R. 33 E., in 

Franklin County, Wash. This point is 2% miles west of Snake 

Eiver, 30 miles northeast of Pasco, and about 10 miles southwest of 

Kahlotus. As shown on the Wallula topographic map, the altitude 

of the cut is about 1,350 feet, and that of the top of the adjacent hill 

is about 1,500 feet. A general view of the locality is given in Plate 

7,5.

The two road cuts are about 50 yards apart, and both contain 

elephant bones, rodent remains, and shells that appear to be those 

of air-breathing gastropods. As the cuts are nearly at the same altitude and the matrix is similar it is assumed that they represent the 

same horizon. Preliminary work showed that the southern cut was 

the more promising, and effort was concentrated at this place. At 

the end of the five days of excavation a hole had been dug in the 

bank 10 feet wide, 8 feet deep, and having a back face 12 feet high. 

Bones were being obtained with decreasing frequency, and when this 

high face caved work was abandoned.

The bulk of the bones belonged to a single elephant. All the 

major bones were recovered except the skull. This material has been 

examined by Drs. 0. P. Hay and J. W. Gidley, who point out that 

the individual was very old, as shown by the condition of the teeth. 

The right side of the lower jaw had suffered a lesion, well shown in 

the photograph reproduced as Plate 7, A. The lesion appears to have 

been a pus cavity and extended into the tooth, part of which was 

lost by decay during the animal's life. The age of the animal and 

this pathologic condition make identification of the species difficult, 

but Doctors Hay and Gidley believe that the remains are those of an 

elephant identical with or near to Elephas cofambi.

The horse tooth found in the northern cut and the invertebrate 

shells have not yet been identified. The rodent material, though not 

studied in detail, seems according to Doctor Gidley to belong to 

species yet living in the region.

It is evident that these fossil remains are of- Pleistocene age, but 

unfortunately Elephas columfoi, as at present defined, is not characteristic of any particular part of the Pleistocene epoch. Of the 

rodent remains some are the bones of animals like those that to-day 

make burrows in the soil to depths of 4 or 5 feet. Others were 

found as single isolated bones, generally the relatively durable lower 

jaws, in undisturbed ground and were contemporaneous with the 

elephant, whose bones, as noticed below, are gnawed by similar 

animals. That Pleistocene forms of rodents are indistinguishable 

from those of the present day in the imperfect material collected 

does not, however, seem remarkable,
36 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926 

ARRANGEMENT OF THE FOSSIL. BONES

The lack of definition in age is unfortunate, but the arrangement 

of the bones has real significance in relation to the origin of the 

" Palouse soil." At this locality the soil is a light-buff or pale-brown 

very fine sand and would be classed with the Bitzville soil series in 

a soil survey by the Bureau of Soils. It has so little clay that it 

lacks cohesion when dry and handles much like dry Portland cement. 

There is no stratification nor vertical structure except in a zone 

about 5 feet thick that conforms to the hill slope. Here there is a 

pseudovertical structure similar to that noted by the Bureau of 

Soils as general in the Bitzville series. In this zone the burrows of 

small rodents are numerous. The upper 2 feet is somewhat more 

compact than the lower 3 feet, perhaps because of alternate wetting 

and drying. The whole zone is somewhat more pulverulent than the 

material below, which, however, is similar in grain and color. In 

places the grains of the lower part are agglutinated in limy nodules, 

and there are a few irregular seams of calcium carbonate. Cementation is so incomplete, however, that all the material can be excavated 

with a shovel. Only one pebble was found. It is of irregular shape 

with rounded edges, about 1^ inches on the major axis, and composed of basalt.

In this mass the bones of the elephant had a vertical range of 6 

feet and a horizontal range of 10 feet along the face of the road cut 

and of 8 feet into the interior of the hill. They were arranged without order or system. For instance, the lower jaw was upside down 

and under one shoulder blade; single foot bones and vertebrae were 

found in various parts of the excavation. When buried most of the 

bones were in nearly perfect condition except one shoulder blade, 

most of the ribs, which were found in separated pieces, and the tusks, 

of which fragments were found scattered throughout the excavation. 

The skull was missing. The pelvis was imperfect, but this condition 

is probably due to surface weathering since burial and to damage in 

the excavation of the road cut.

The bones must have lain on a surface for some time after the 

animal's death, for many of them retain the marks of gnawing by 

rodents. These marks alone seem adequate proof that the bones lay 

on a dry land surface. The scattered fragments of tusks and of bones 

seem also proof that the skeleton lay on the surface long enough for 

some weathering of the bones. The bones were, however, entombed 

and placed in position before fossilization and while yet retaining 

some resiliency, for one entire rib, free from cracks, was found in a 

nearly vertical position. In its present state it can hardly bear its 

own weight in this position and could stand no rotation or creep in 

the inclosing sand. It must have attained the vertical position and
) THE (l PALOUSE SOIL '' PROBLEM 37

have been inclosed in the sand while yet retaining the tensile strength 

of green bone.

Thus the arrangement and characteristics of the bones indicate 

that the elephant died on a land surface. The very fine sand of the 

inclosing matrix is similar to that found in hummocky areas where 

constant shifting by wind takes place. Doubtless each bone formed 

an obstruction to the wind, and a pit was dug out below it on the 

windward side into which it fell and was buried. This process may 

have taken place several times, but some of the bones were quickly

/ buried, or they would not have been preserved in such perfect condition. In most sandy areas of this type it is difficult to determine 

whether there is more erosion than deposition, but deposition must 

have been dominant at the time in this area, for not only were the 

bones buried in the wind-blown sand but more material of similar 

character was accumulated to a minimum height of 10 feet.

If it is granted that the foregoing analysis is correct and that the 

elephant died and was buried in an eolian deposit, it follows that the 

land in this area had a scanty vegetative cover and that the climate

':> was doubtless arid. The elephant is, however, a gross feeder and

must live in areas of heavy vegetation. This individual may have

been merely passing through the region or may have come to this

place to die, as is the reported habit of African elephants.

As further collecting at this locality will doubtless produce other

'' bones, some of which may have a greater stratigraphic value than 

these elephant bones, it is worth while to consider whether the windborne material of this locality represents the " Palouse soil " or only 

a part of it. An inspection of Plate 7, 5, shows that the road cut

/ lies at the base of a poorly defined terrace, about 150 feet below the 

top of the adjacent hill. The nearest outcrops of basalt are a 

quarter of a mile away. If the top of the adjacent hill represents 

the top of the plateau and if the road cut is in the " Palouse soil," 

we must assume that this original mantle is 150 feet thick in this

i locality. Well records and other observations in the vicinity indicate that it is not more than 70 to 100 feet thick, and consequently 

it seems probable that the road cut was made in a terrace that is 

composed largely of wind-worked material and lies below the general level of the original mantle of " Palouse soil." Such vaguely 

defined terraces may be seen on many minor streams and seem to

.' correspond to the pause in erosion marked by the gravel terraces of 

Old Maid Coulee. (See p. 27 and Pis. 4, 0 and 5, B.)

Old Maid Coulee and similar valleys were formed in a cycle of 

erosion that antedated the great coulees produced by the diversion 

of glacial waters over the plateau. By this line of reasoning the 

terraces and specifically the terrace from which the elephant bones 

were dug are pushed far back into Pleistocene time.
38 CONTRIBUTIONS TO GEOGEAPHY OF UNITED STATES, 1926

Speculation on the geographic conditions of that time is in the present state of knowledge necessarily hazardous, but it may well be that 

in those days the deep canyons of Columbia and Snake Elvers did not 

exist. The valleys of these great rivers may have been broad and 

shallow. The flood plains, periodically overflowed and with a high 

water table, may have supported a broad strip of dense vegetation. 

Here the elephants may have lived in oases in a land as arid or 

even more arid than that of central Washington to-day. In the 

area between these river flats fine sand, derived from the original 

" Palouse soil" and from the broad river channels in the long 

period between the annual floods, may have been shifted to and fro 

by the wind, and in this sandy area an elephant who lived in the 

near-by wooded river flat may have died and left his bones,

PRESENT ACCUMULATION OF LOESS 

DUST STORMS

Kemarkable dust storms are features of the climate of eastern 

Washington. These storms and the inferred wind work indicated 

by the asymmetric shape of the hills, as first noted by Kussell,29 

have led to the theory of accumulation of the " Palouse soil " as windborne dust through a period extending into the present.

Peterson 30 collected and weighed dust that fell on measured areas 

of new snow near Moscow, Idaho, in four storms within a period of 

55 days. The individual falls ranged from 140 to 585 pounds to 

the acre for the period. Assuming a similar rate of fall throughout, 

he obtained a rounded figure of 7,500 pounds to the acre as the 

yearly accumulation of dust. As the observations extended over 

a period of only 55 days in only one year, the figure of 7,500 pounds 

to the acre involves violent assumptions. However, in continuance 

of Peterson's argument, if this rate of fall is projected into past time 

the soil has been accumulating at the rate of 4 inches a century. 

Under this assumption a thickness of 75 feet would require, for its 

accumulation, 25,000 years.

A slightly greater daily fall is recorded by Larsen,31 who measured 

the dust that fell in a single day's storm in March, 1917, in northern 

Idaho, and obtained a figure of 600 pounds to the acre.

It is unfortunate that systematic measurements of dust falls have 

not been made, for all observers agree that the fall of dust is very 

irregular in amount even in recognized " dust" storms, and there 

is also an invisible fall of dust which takes place daily during the

20 Russell, I. C., op. cit.

s? Peterson, P. P., Rate and mode of soil deposition in Palouse area of Washington and 

Idaho: Science, new ser., vol. 55, pp. 102-103, 1922.

31 Larsen, J. A., Soil shifting and deposits: Science, new ser., vol. 50, p. 457, 1922; 

Dust storms of northern Idaho and western Montana: Monthly Weather Review, vol. 

52, p. 110, 1924.
THE ' PALOUSE SOIL' PEOBLEM 39

summer. The observations of Peterson and Larsen, which are tabulated below, have their principal value in giving the order of magnitude of the quantity of dust that falls in single storms:

Summary of measured dust falls in Idaho, 1917

Locality

Do....................................................

Do..... .... .........................................

Do....................................................

Observer

Peterson ..........

.....do.............

...do.....

.....do.............

Larsen ............

Date

Jan. 29,1917

Mar. 21, 1917

Mar. 22, 1917

Mar. 23, 1917

March, 1917

Amount 

(pounds 

to the 

acre)

140

196

184

585

600

The average fall is 341 pounds to the acre for each storm, equivalent to a depth of 0.00013 foot, or 0.0016 

inch.

A record of the principal dust storms at Spokane, Wash., has been 

kept at the local office of the United States Weather Bureau as part 

of the daily written notes on incidental phenomena of the weather. 

Through the kindness of Mr.. E. M. Keyser, the local forecaster, this 

information with other pertinent data has been tabulated and put at 

the writer's disposal. Although the recording of dust storms is not 

a part of the forecaster's required task, Mr. Keyser believes that all 

the important storms have been recorded but that storms of minor 

intensity may easily have been missed.

Dust storms at Spokane, Wash., 1905-1925 

[Eecorded by E. M. Keyser, United States Weather Bureau]

Year

1905 

1910 

1911 

1913 

1913 

1913 

1913 

1914 

1915 

1916 

1917 

1918 

1918 

1918 

1918 

1918 

1918 

1919 

1919 

1920 

1920 

1920 

1920 

1920

Date

Aug. 27 

June 1 

May 5 

Mar. 29 

Apr. 21 

July 6 

Oct. 13 

Aug. 6 

Oct. 31 

June 18 

Mar. 23 

May 30 

June 9 

July 9 

Aug. 8 

Aug. 26 

Oct. 11 

Apr. 24 

July 5 

Apr. 5 

Apr. 7 

May 17 

May 21 

June 22

Observer's statement

Dust and rain- _________________

Dust............................................

Dust and rain.. __ _ . . _ _ _ .. _ ..

Dust preceded by rain.... .. _ _ ___ ..

.....do... ........................................

Dust and rain... _________________

.....do...........................................

Dust preceded by rain.... __________ ...

.....do.......... _ ......... _ ..................

Light dust and light rain.... ______ . ........

Light dust.... . .-....- ___ ...

Light dust and light rain __ __________

Light dust. _ __ .... ___ .

Intense dust... ____ .

Light dust __ ____ . ___ . ........ 

Dust..... . .... .............. .

.....do..... ...............

Dense dust preceded by rain _________ 

Dust...........................................

Some dust durinc afternoon _ _____ _ ...

Wind

Velocity 

(miles per 

hour)

39 

35 

25 

30 

36 

28 

39 

23 

44 

23 

40 

30 

26 

38 

24 

26 

31 

27 

27 

23 

28 

39 

24 

26

Direction

SW.

sw.

SW.

sw. 

sw. 

w. 

w. 

sw. 

sw. 

sw. 

sw. 

sw. 

sw. 

sw. 

w. 

w. 

sw. 

sw. 

sw. 

w. 

sw. 

sw. 

sw. 

s.

Accumulated rainfall from Jan. 1 

to date given 

(inches)

Normal

11.23 

8.65 

7.23 

5.59 

6.61 

10.54 

13.07 

10.98 

13.87 

9.64 

5.27 

8.55 

9.04 

10.61 

11. 00 

11. 20 

12.97 

6.75 

10.40 

5.92 

6.00 

7.92 

8.12 

9.86,

Actual

11.18 

5.84 

2.78 

5.06 

5.92 

9.09 

12.79 

8.68 

10.83 

8.48 

3.08 

4.90 

4.90 

5.34 

5.59 

5.85 

6.28 

7.64 

8.44 

2.42 

2.42 

4.10 

4.10 

4.97
40 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926 

Dust storms at Spolcane, Wash., 1905-1925 Continued

Year

1920 

1920 

1921 

1921 

1921 

1921 

1921 

1921 

1922 

1923 

1923 

1923 

1924 

1924 

1924 

1925

Date

June 23 

June 24 

Apr. 21 

Apr. 22 

Apr. 29 

Aug. 14 

Sept. 26 

Sept. 27 

Aug. 19 

Mar. 16 

Mar. 19 

Oct. 16 

Apr. 18 

Aug. 3 

Sept. 8 

July 24

V

Observer's statement

Dust settled during morning... .

Dust and rain, much dust brought down.. ......

.....do. .......................................

Great clouds of dust _ .........................

Dust... ________ . _____ ........ __ ..

.....do..........................................

Heavy dust. ___ __ _ ... _ ... _ . ...

Dust and light rain....... __ . ..... _ ...

Dust.... __ ....................................

Dust and rain (driving in automobile difficult)..

Light dust, light rain . ____________

Wind

Velocity 

(miles per 

hour)

22 

18 

20 

28 

33 

39 

33 

39 

28 

30 

40 

29 

30 

23 

36 

30

Direction

S. 

S. 

SW.

w.

. sw. 

sw. 

sw.

sw. 

sw.

N.

sw. 

sw. 

sw.

NW. 

S.

s.

Accumulated rainfall from Jan. 1 

to date given 

(inches)

Normal

9.90 

9.94 

6.61 

6.66 

6.95 

11.06 

12.26 

12.29 

11.11 

4.95 

5.07 

13.22 

6.46 

10.85 

11.73 

10.83

Actual

4.97 

4.97 

5.81 

5.86 

5.91 

6.58 

7.96 

7.96 

6.71 

4.02 

4.05 

12.77 

3.20 

4.64 

5.55 

7.94

NOTE. The record is complete to October 15,1925.

As described in notes by Mr. Keyser, the dust storm of August 19, 

1922, began in the middle of the forenoon and lasted until after 

sunset. The dust was so dense that it shut out the sky, and the sun 

had the appearance of a very pale moon. At Newman Lake, east 

of Spokane, the view across the lake was obscured as by a dense fog.

The storm of October 16, 1923, was seen by the writer. The dust 

was so thick as to have the appearance of a yellow fog, and in combination with the clouds, from which rain shortly fell, it produced 

a yellow darkness in which it was nearly impossible to see one's way. 

Automobiles were abandoned because of the difficulty of driving. 

When the rain began the first drops were liquid mud, which made 

great brown patches on umbrellas and clothing. The window panes 

in Spokane, the next morning, were so dirty that it was impossible 

to see through them, and for several days the roofs of buildings 

retained a thin coat of mud acquired during the storm.

It is obvious from the foregoing accounts that the dust storms of 

the eastern portion of the Columbia Plateau are extraordinary 

phenomena. During these storms immense quantities of dust are 

taken into the air, to be later deposited. The storms are well worth 

further study to determine more precisely the direction of movement 

of the dust, the places where it is picked up, and the places where 

it is deposited.

The Spokane record furnishes the only available group of facts 

to confirm general observation. From this record the following conclusions can be reached:

1. The wind velocity during storms ranges from 18 to 44 miles 

. per hour.
THE l ' PALOUSE SOIL '' PROBLEM 41

2. The wind is generally from the southwest, sometimes south, and 

sometimes west. Only one dust storm had wind from the north, and 

there were none with wind from the east.

3. Every storm, except that of April 24,1919, occurred when there 

was a deficiency of rainfall, as shown by the two columns at the 

right in the table on pages 39-40, giving the normal accumulated precipitation from January 1 to the date of the storm and the actual 

accumulated rainfall for that year.

4. In the 21 years 1905 to 1925 covered by the record there were 

19 storms recorded as " dust and rain," or an average of about one 

such storm a year.

The dust storms originate to the southwest of Spokane, but how 

much of the dust comes from a distance is uncertain, particularly as 

the incidence of the storms coincides with deficient rainfall at Spokane. However, general testimony of persons familiar with the 

region indicates that some storms originate in northern Oregon and 

sweep across the whole of the Columbia Plateau. From the same 

source it is learned that the dust storms were unknown before the 

settlement of the country west of Spokane and the Palouse region. 

Vast areas once protected from the wind by a natural growth of 

sagebrush and grass have been plowed and many roads have been 

made in the Big Bend country since about 1900. Here the movement 

of dust can be seen on any windy day. In places roads have been 

filled to the tops of the fences with fine sand derived from adjacent 

fields. The great area of plowed ground left exposed to the wind 

from spring until fall under the system of summer fallow for the 

production of wheat, together with the dryer climate of the western 

portion of the plateau, provides a source for a large quantity of dust. 

It is natural to expect, therefore, a transfer of dust from this dryer 

area to the more humid area in the east.

BATES OF ACCUMULATION AT PRESENT AND IN THE PAST

If, as seems reasonable, the dust storms of the present time tend 

to deposit dust in the eastern section of the Columbia Plateau, it 

does not follow that such accumulation is the sole cause of the formation of the " Palouse soil" or that the present rate of deposition 

is a measure of the time involved in the process, as argued by 

Peterson.

The unconsolidated mantle over the basalt is apparently as thick 

in the western part of the plateau as in the eastern part, yet at the 

present time most of the dust picked up by wind in the western part 

of the plateau arises from roads and fields in the " Palouse soil" 

areas. This fact alone would indicate that the main body of the 

" soil" was deposited at some time in the past and that the present
42 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

action merely modifies the distribution of soil brought about bj that 

past action.

However, there is another group of facts which throws light on 

the problem. The unequal thickness of wind-borne or loessial soil 

in the eastern part of the plateau has been noted in the several 

soil surveys. On the basalt plateau there is above the inner core of 

the hills, which consists in places of reddish or yellow fine-grained 

material, thought to be old loess, and of ancient till, 3 to 6 feet or 

more of soil. A similar material of the same or less thickness but 

resting directly on the rock is found on the flanks of plateaus, and 

generally on granite and gneiss.

Still more significant, however, is the almost total absence of such 

soil on the terminal moraine of the intermediate glaciation and on 

the ground moraine and rock surfaces attributed to the ice of that 

stage in the area between Cheney and Spokane. Similarly, the 

top of the outwash gravel 32 of the intermediate ice, which was left as 

a terrace along Latah (Hangman) Creek, has no dust cover. On 

the successive terraces, carved from this outwash gravel by Latah 

Creek, there is 1 inch to 6 inches of dust. Remnants of the Wisconsin outwash plain show as a terrace along Spokane River, and 

on this surface there is no accumulation of dust.

On Pleasant Prairie, a plateau remnant north of Spokane, there 

is a loessial soil mapped as part of the Palouse series in the soil 

survey. This soil underlies the flat areas between minor streams 

that lie 50 to 200 feet below the surface of the plateau. The soil 

is absent, however, from the terraces and heaps of gravel that border 

these valleys and from a large gravel terrace on the south side of 

Pleasant Prairie. Glacial till that lies in patches on the slopes, 

particularly the north slopes of the prairie, is also free of dust. 

All these accumulations of gravel and till can be attributed to the 

intermediate glacial ice, which seems to have surrounded Pleasant 

Prairie without overriding the main part of it. The gravel appears 

to have been largely deposited by streams that ran across the surface of the little plateau from one part of the surrounding ice to 

the other.

Between the small valleys with their bordering heaps of gravel 

loessial soil to a depth of 18 inches to 3 feet forms smooth plains 

and overlies a compact glacial till. As may be seen in Plate 7, #, 

the soil is generally dark, and its friable nature is in marked contrast to that of the underlying till, which is rusty, compact, and 

much decomposed. Many well-striated and soled pebbles occur in 

the till, which is an unmistakable glacial product and long antedates

32 For a brief description of the gravel at Spokane, see Pardee, J. T., and Bryan, Kirk, 

Geology of the Latah formation in relation to the Columbia Plateau : U. S. Geol. Survey 

Prof. Paper 140, pp. 15-16, 1925.
THE PALOUSE SOIL'' PKOBLEM 43

the intermediate glacial stage, representing some earlier glacial advance. Similar loess overlying old till can be seen along the new 

county highway on Fivemile Prairie.

Thus, near Spokane 18 inches to 3 feet of loess overlies an early 

till, but no dust has accumulated on the intermediate till or on the 

Wisconsin terrace. In the sheltered depression of the Latah Creek 

valley a small amount of dust overlies the recessional terraces cut 

by the creek in the outwash plain of the intermediate ice.

The city of Spokane lies in an area covered by perennial grass and 

containing open forests of pine trees, where wind-borne dust should 

be and 'probably is deposited easily, yet the deposition of dust near 

Spokane has in the past been at a moderate rate, and almost none has 

been deposited since the disappearance of the ice of the intermediate 

glaciation.

Owing to the lack of quantitative observation on dust falls, the 

present rate of deposition can be merely approximated, but even 

under the most conservative assumptions it is obvious that the present 

rate greatly exceeds that of the past. Those dust storms in which 

rain accompanies the dust should be the most effective in deposition, 

for the rain carries the dust as mud down to the ground, where it can 

be entangled in the grass. The gravelly surface of the Wisconsin 

terrace is flat and has no surface run-off, so that it is an excellent 

place to receive the dust from such storn.^, and the dust once deposited should remain in place. As shown in the tabulated record 

of the dust storms at Spokane (pp. 39-40), there has been an average 

of one of these storms a year. No direct measurement of the quantity 

of dust deposited by storms at Spokane is available. The observations of Peterson and Larsen, the only measure of the quantity of 

dust deposited, were made many miles distant from Spokane. It 

may be also that, being made in January and March, they do not 

apply to all the storms listed in the Spokane record, most of 

which occurred in the summer and fall. However, the average of 

their observations, 341 pounds to the acre, or 0.0016 inch in depth, is 

doubtless of the correct order of magnitude and may be considered 

the minimum yearly rate of dust falls in Spokane.

The length of time during which the Wisconsin terrace at Spokane 

has been exposed to the fall of dust is of course uncertain. It is 

reasonably well established that the last Pleistocene glaciation of tho 

northern Rocky Mountains coincides with the Wisconsin glaciation, 

as known in the Middle West. Most authorities place the final 

retreat of the Wisconsin ice front in North America and Europe at 

a time 10,000 to 20,000 years ago.

As the outwash plain on Spokane Hiver was deserted by glacial 

water shortly after the ice began to recede, it would be safe to assume
44 CONTRIBUTIONS TO GEOGRAPHY OF UNITED STATES, 1926

that this plain has been prepared to receive dust from the beginning 

rather than the end of ice retreat. However, for the sake of conservatism 10,000 years may be assumed as the available time. At 

the rate of deposition of 0.0016 inch to each storm, obtained by the 

use of the data of Peterson and Larsen, and on the assumption of 

one storm a year, the total deposit on the Wisconsin terrace should 

be 16 inches, whereas actually no dust can be detected. This calculation also takes no account of dust storms unaccompanied by rain, 

though doubtless these storms also deposit dust, and there is probably 

also a continuous invisible fall during the summer.

By this line of reasoning, therefore, it is apparent that the present 

dust storms probably deposit dust at a greater rate than at any time 

since the Wisconsin glaciation. The times following both the intermediate and the Wisconsin glaciations must have witnessed very 

little fall of dust, else dust would be found on the till and outwash plains of the intermediate glacial stage. We are, therefore, almost forced to conclude that the original deposition of dust took 

place under conditions of topography and climate that may have 

been markedly different from those prevailing to-day or at any time 

since the intermediate glaciation.

In the western part of the Columbia Plateau the amount of soil 

shifting since the time of the intermediate glaciation may have been 

somewhat greater, especially near large tracts of " Palouse soil." 

The so-called scablands 33 are generally bare or have only scattered 

patches and circular mounds of wind-borne soil. If most of these 

scabland areas date back to the intermediate glaciation, as contended 

by Bretz, then the foregoing argument as to past rates of deposition 

near Spokane applies also to the western part of Columbia Plateau.

CONCLUSIONS

In the foregoing discussion of the "Palouse soil" problem some 

new facts are brought forward, but these facts are insufficient to 

give a complete analysis of the genesis of these interesting and 

economically important deposits. The data are presented to clarify 

the issues and to make available to others the facts that have been 

gathered. The inner core of the "Palouse soil" hills remains as 

much a mystery as ever, but it is obviously a complex and relatively 

ancient deposit whose story, if known, would illuminate the history 

of Pleistocene time on the Columbia Plateau.

The following conclusions seem justified:

1. The soil that is useful in agriculture (Palouse, Bitzville, Helmer 

series, etc., as defined by the Bureau of Soils) consists of a top

33 Bretz, J. H., The channeled scablands of the Columbia Plateau: Jour. Geology, vol. 

31, pp. 623-634, 1923. See also Freeman, 0. W., Scabland mounds of eastern Washington : Science, new ser., vol. 64, pp. 450-451, 1026.
THE "PALOUSE SOIL" PROBLEM 45

skin, or veneer, that is largely wind borne throughout the plateau 

and rests on material of various sorts.

2. Where the unconsolidated material, or so-called " Palouse soil," 

is thick the inner core of the hills composing the intricate topography 

is largely unknown. At various places this inner core consists of (1) 

laminated silt, (2) almost structureless reddish compact silt with 

limy concretions that may be a loess, (3) yellow clay and clay silt 

that seem with little doubt to be loess, (4) ancient glacial till 

(older than the intermediate till of this region), and (5) very doubtfully a residual soil derived from basalt.

3. In the western part of the plateau there is in numerous valleys 

a well-defined terrace in part underlain by gravel. The valleys and 

the terrace antedate the great coulees formed by glacial waters.

4. The soil on these terraces is a definite wind-deposited material, 

jis shown by the arrangement of the bones of an extinct elephant.

5. The soil on the terraces is younger than the unknown inner 

core of the adjacent " Palouse soil " hills but is of Pleistocene age.

6. In the eastern part of the plateau thin and discontinuous layers 

of gray to green-gray material residual from basalt underlie yellow 

clay composed of minerals foreign to the basalt and having all the 

characteristics of loess.

7. In one place at least the top layer of soil or veneer contains 

volcanic ash.

8. The present rate of deposition of dust in the vicinity of Spokane 

is an accelerated rate induced by the cultivation of immense areas of 

loessial soil to the west and south.

9. Deposition of loess since the Wisconsin and intermediate bodies 

of till were laid down has been moderate in amount, and the great 

period of deposition of wind-borne soil antedates these later advances 

of glacial ice.
INDEX

Page 

Acknowledgments for aid. _ _.. _. ____ 19,22,39

Basalt, decomposed, description of-____ 29-30

decomposed, photomicrograph of--___ 34

hillock of columns of, plate showing.. _ 2

microscopic.study of chips of....____ 4-5

pedestal rock in..____________ 3-8

plate showing....__________ 2

weathered, partial analyses of.....___ 5-6

Colfax, Wash., Palouse soil near_.____ 30 

Columbia Plateau, rolling hills of, plate showing.............................. 34

Connell, Wash., silt near......._______ 2&-27

Coulees, Palouso soil in_________.__ 27-28 

Crown Point, N. Mex., climate at........... 10-11

pedestal rocks near..__________ 11-13

Dust, rate of accumulation of.._______ 41-44

Dust storms, fall of dust in....____.. 38-39,43

occurrence and features of....._____ 39-41

Elephant, Pleistocene, fossil bones of.-... 35,36-37 

Pleistocene, lower jaw of, plate showing.. 34

Expansion and contraction, thermal, fracture

of rock grains by......_____ 6

thermal, spalling of rock by.__ .. 6

Fishtrap, Wash., road cut at, plate showing. 34

road cut at, soil in____________ 28-29

Frost, action of, in spalling rocks....____ 6,8

Glacial deposits, relation of loess to..____ 43-44 

Gravel, terraces of, covered with loess....... 27

terraces of, covered with loess, plates

showing_____________ 34

Helmersoil, features of..__________ 25 

Humid regions, pedestal rocks in______ 13-15

Insects, pitting of rocks by...._______ 13

Jemez Creek, N. Mex., pedestal rocks in

canyon of, plate showing._ ___ 2

shaping of pedestal rock near._____ 8-9

Jemez Hot Springs, N. Mex., rainfall at__ 9

Kahlotus, Wash., fossil locality southwest of. 35 

Keyser, E. M., acknowledgment to____ 22,39

Loess, dust storms depositing.._______ 38-41 

exposures of, plates showing. ______ 34 

from Council Bluffs, Iowa, photomicrograph Of.................____ 34

rates of accumulation of.._______ 41-44

Martel, E. A., opinion on the shaping of

pedestal rocks._________ 1-2 

Moraines, absence of dust from_______ 42 

Moscow, Idaho, dust falls at....._____ 38,39

46

Old Maid Coulee, erosion and deposition in 

soil in.-.-..-.-____'_.____.....

Palouse soil, bedding in.... ______ 30 

conclusions on.. ..__.. 44-45 

earlier descriptions of._________ 22-26 

fossil bones in, arrangement of_____ 36-38 

discovery of.._____________ 34-35 

general features of..._._________ 21-22 

geographic conditions during deposition

of----- . . ... ... 38 

hills of, near Hillcrest, Wash., plate showing---.----.--.----- . 34 

microscopic study of..... _____ 31-32 

photomicrograph of clay from....___ 34 

photomicrograph of upper layer from__ 34 

rate of accumulation of..________ 41-44 

source of----- ___________. ___ 33-34 

topography in areas of, plates showing_ 34

Pardee, J. T., cited 29-30

Pedestal rocks, in basalt, shaping of..___ 3-8 

in sandstone, shaping of.________ 10-13 

methods of shaping..__________ 1-3 

shaping of, by diferential rainwash.. _ 8-9

Pleasant Prairie, Wash., gravel surrounding- 42 

loess on............__________ 42

road cut on, Palouse soil in_______ 33 

plate showing...____._____ 34

Rainwash, differential, pedestal rocks shaped

by..--- 8-9,12 

Rio Salado, N. Mex., channel erosion of.__ 17-19 

Ritzville soils, features of __________ 23,26 

Rosalia, Wash., soil in road cuts near____ 29 

Boss, Clarence S., microscopic study of basalt

chips by.____._______ 4-5 

microscopic study of Palouse soil by__ 31-32

Sand, wind-blown, action of _________ 3,13 

Sandstone, pedestal rocks in. ______ 10-13

pedestal rocks in, piates showing..___ 2 

Santa Rita, N. Mex., surveys of______ 18 

Sapping, differential, process of______ 9-10,12 

Spalling, causes of ___. ____. _____ 6

change in shape of rocks by..______ 4 

Spangle, Wash., section of Palouse soil near.. 30 

Spokane, Wash., dust storms at, 1905-1925... 39-40

wind-borne dust near_ _____ 43 

Stacks, production of _____________ 2-3

Thorn, W. T., jr., acknowledgment to. 19

U. S. Bureau of Soils, surveys by, in Washington and Idaho__________ 23-25

Volcanic d6bris, in Palouse soil_____ 31-32,33

Weathering, chemical, effects of..._____ 7

Wheat, soil for, in Washington..______ 21

Wheeler, Wash., pedestal rock near.____ 3-8

o