University of Virginia Library

THE PUEBLO BONITO EXPEDITIONS

Twenty years after the Hyde Expeditions came to an end and prior
to the announced publication of Pepper's field notes, the National
Geographic Society authorized the explorations reported herein and
previously. Originally planned for 5 years but subsequently extended
two more, the Pueblo Bonito Expeditions were expected to discover
what factors had brought about the extraordinary Chaco Canyon
civilization in what had come to be an unwatered, impoverished, and
relatively uninhabited region. The Society's Committee on Research
desired to identify the builders of Pueblo Bonito, if possible; to discover
where they came from and where they went. The agricultural
possibilities of the valley in prehistoric times, its then sources of water
and fuel, and the location and extent of the ancient forests that had
furnished timbers for the roofs of Pueblo Bonito and neighboring
communities likewise were subjects for inquiry (Judd, 1922a, p. 117).
Not until Pepper's volume appeared in the early summer of 1921 was
it known that comparable studies had originally been planned for the
Hyde Expeditions (Wissler, in Pepper, 1920, p. 1).

On the ground plan herein (fig. 2) rooms numbered 1-190 are
those opened by the Hyde Expeditions. To correlate our studies with

Fig.2__Ground plan of Pueblo Bonito with cross sections
A-A′, B-B′, and C-C′. (From the original survey of Oscar B.
Walsh, 1926)

theirs, rooms excavated for the National Geographic Society likewise
were numbered, beginning with 200, but our kivas were lettered.
When we had exhausted the first kiva alphabet we began a second,
each letter prefixed by the numeral 2. In both text and tables, room
numbers followed by the letters B, C, or D indicate, respectively, the
second, third, and fourth stories.

Of those bearing our numbers, Rooms 210, 227, 295, 299, 300 and
Kivas Y and Z were cleared by unknown persons between 1900 and
1920. We numbered but did not excavate Rooms 205-208, 297, and
301-303; Kivas O, P, S, and 2-C were merely tested for pertinent
information. It was my personal hope that these 12 and all those left
unnumbered might be reserved for examination some years hence.

Except as noted hereinafter, we made no inquiry in rooms excavated
by the Hyde Expeditions, 1-190. During our third season,
however, the better to control surface drainage in the older section
north of Kiva 16, we removed or leveled quantities of excavation
debris left by our predecessors (pl. 5, lower). It was this effort,
perhaps, that prompted Hewett (1921, p. 17; 1930, p. 302; 1936,
p. 32), to state that I had unknowingly excavated rooms cleared and
refilled by the Hyde Expeditions.

After Pepper's 1920 volume became available we utilized his
recorded field notes as fully as possible. But there were additional
data that seemed essential to the history of Pueblo Bonito.

Extramural stratigraphy.—Two conspicuous refuse mounds, the
principal village dump, lie immediately south of the great ruin. Refuse
heaps normally reflect the cultural changes of any community and
potsherds provide a convenient means for measuring such changes
in a prehistoric settlement. Since discards at the bottom are naturally
older than those above, one of our first undertakings in the spring of
1921 was a 5-foot-wide trench through a previously undisturbed
section of the West Mound, larger of the two. A stratigraphic
column, 3 feet square, at the end of that trench reached clean sand
at a depth of 19 feet 5 inches (pl. 6, left). From 23 unequal layers
floored by ash, variously colored sand, or otherwise, we collected 2,119
potsherds (U.S.N.M. No. 334180).

That sherd collection disclosed a puzzling mixture of pre-Pueblo
and later pottery types, top to bottom. There were 93 fragments of
Plain-banded Culinary ware and 778 fragments or 36.7 percent, of
Corrugated-coil. Early and late varieties of Black-on-white were
present in all 23 layers; Black-on-red, in more than half. Straight-line
Hachure occurred in every stratum except the two lowest, V and W.

Brown-with-polished-black-interior occurred in all but five strata:
B, S, U, V, and W. A single Mesa Verde sherd was recovered in
Layer E, the bottom of it 3 feet 7 inches below the surface. ProtoMesa
Verde fragments appeared above the 9½ foot level but not
below. This 20-foot intermixture of early and late pottery came as
such a complete surprise I questioned our findings and cut another
column.

Next, I undertook to examine surrounding soils by means of 7 pits,
4 to 12 feet deep, dug at various distances and in various directions
from Pueblo Bonito. None exhibited more than stratified sand, windblown
and water-washed, with intervening silt layers, occasional
lenses of gravel, bits of charcoal, and chance potsherds. A humus
layer that might have identified a once-cultivated field was nowhere
seen. And, despite a secret hope, none of my seven pits revealed any
trace of the long-sought Bonitian burial ground.

We began our second season with a third column through West
Mound rubbish and followed it with an East Mound test. Two years
later we tried both mounds again. Then, in 1925, after my own
efforts had failed, I invited Frank H. H. Roberts, Jr., to join my
field staff and take charge of the local problem in stratigraphy. The
invitation was extended upon recommendation of Dr. A. V. Kidder,
a long-time friend and confidant, and chiefly in recognition of
Roberts's convincing analysis of BM.III-P.I pottery from the PagosaPiedra
region, southwestern Colorado. At Pueblo Bonito Roberts was
assisted by the late Monroe Amsden after the latter, under special
permit from the Department of the Interior, had concluded a study
of 16 small-house ruins in and south of Chaco Canyon (U.S.N.M.
Nos. 329803-45).

As graduate students in anthropology Amsden, at Washington,
D. C., and Roberts, in Cambridge, Mass., had assisted during the
winter of 1924-25 in analyzing the Pueblo Bonito potsherds I had
previously collected. Failing health compelled Amsden to relinquish
his part in this joint undertaking thus leaving to Roberts principal
responsibility for our study of Pueblo Bonito ceramics, a study that
had made scant progress prior to unexpected discoveries early in 1925.

Intramural stratigraphy.—During our fourth season, 1924, we had
cleared the West Court to its last recognizable occupation level (pl.
7, upper) and, in so doing, had discovered that village waste and
blown sand were piled up 6 feet 7 inches—almost ceiling high—against
the outer east wall of Old Bonitian Rooms 329-330. Consequently
one of our first tasks of the 1925 season was to seek explanation for

that accumulation. We made a number of tests close along the west
side of the Court and then, boldly, extended our 1921 West Mound
trench to the ruin and northward to Kiva Q.

That extended trench (pl. 6, right), 5 feet wide and 12 feet deep,
solved our 4-year-old puzzle, the mixture of early and late village
refuse. At a depth of 10 feet 2 inches we came upon the floor of a
Great Kiva, over 50 feet in diameter, built inside a huge excavation
expressly dug in a vast accumulation of household rubbish and later
completely razed. Rubbish from that excavation, nearly 2000 tons of
it, may well have started the West Mound—the mound we had profiled
4 times, 1921-1924. Sandstone spalls and chunks of dried mortar
from the razed kiva added to the displaced rubbish. So, too, did
quantities of current floor sweepings.

Just outside the south limit of that razed kiva was a previously
undisturbed section of the original trash pile. Into that remnant
Amsden and Roberts, to whom I had entrusted our entire stratigraphic
study, sank two yard-square test pits the first 13 feet deep and the
second, 12 (fig. 7). As in any other dump, discards at the bottom were
older than those above and the sequence in which they occurred,
bottom to top, provided the information on which Roberts and
Amsden based our knowledge of local ceramics.

Much has been written about the prehistoric pottery of Chaco
Canyon. Beginning with Kidder (1924), archeologists have extolled
the exceptional whiteness of its surface slip, the variety and the perfection
of its hachured designs, the blackness of its paint. More than
one has puzzled over the association there of Early Pueblo and Late
Pueblo vessel shapes and ornamentation, of mineral paint and vegetal
paint—enigmas not solved until Amsden and Roberts cut their two
12-foot-deep tests into sub-court debris at Pueblo Bonito. From
Test 1 they recovered 3,593 potsherds; from Test 2, 2,934.

The 2,934 sherds from Test 2 (U.S.N.M. No. 334175), to limit
this presentation, occurred as follows:

                     

													Percent
Strata	A	B	C	D	E	F	G	H	I	J	K
Black-on-white	97	277	225	130	137	266	132	53	64	2	6	1,389	47
Plain gray	30	173	127	102	117	212	104	48	64	27	8	1,012	35
Broad band	10	55	40	42	50	72	29	7	10	1		316	11
Narrow band						17	5			2		24	1
Nail-cut band	1	4		2	1				1			9	0.3
Waved band			1									1
Corrugated-coil	23	47	43	1								114	3.5
Black-on-red	1	9	9	5	4	14	15	4	5			66	2
Pol. black inter	1	2										3	0.1

Roberts and Amsden separated their 1,389 Black-on-white sherds
into 19 lots including "miscellaneous" (37.5 percent) and those with
no trace of paint (23.9 percent). Of the remainder, design elements
familiar to all students of Pueblo history appeared at various levels
and in the following proportions:

                         

													Percent
Strata	A	B	C	D	E	F	G	H	I	J	K
Straight hachure	4	31	8									43	3.1
Squiggled hachure	6	2	7	3	6	16	7	3	5			55	3.3
Ticked lines	4	10	16	5	15	18	7	6	4			85	6.2
Waved lines		4	5	4	3	7	8	4	1			36	2.6
Stepped triangles	5	16	17	25	9	20	12	4	9			117	8.5
Dotted triangles	6	3	13	15	9	9	9	4	4			72	5.2
Volutes	1	6	7	3	3	13	5	3	3			44	3.2
Checkerboard		1	1		1		3	1				7	0.5
Opposed dentates	1	2	2		1	4	2	1	2			15	1.1
Chaco-San Juan	11	15	5									31	2.3
Mesa Verde		1										1	0.1

To process the vast quantity of potsherds we had previously
recovered from excavated rooms and trenches, Amsden and Roberts
established a workshop in reconditioned Rooms 122-124 at the southwest
corner of the ruin (pl. 4, upper). Here they sorted, counted at
least twice, and classified an estimated 2,000,000 potsherds. After
eliminating all recognizable duplicates there remained 203,188 fragments
for tabulation, and these, coupled with data from West Court
Tests 1 and 2, provide a framework for the history of pottery making
at Pueblo Bonito. At the end of our studies all unwanted sherds were
reburied, many of them in the West Mound cut made for our dumpcars
and track (pl. 5, lower).

In reporting upon the material culture of Pueblo Bonito I paraphrased
some of Roberts's field notes in listing the diagnostic features
by which he and Amsden cataloged their Test 1 and Test 2 potsherds,
and I summarized Miss Anna O. Shepard's identifications of local
pigments and tempering agents (Judd, 1954, pp. 177-183; see, also,
Shepard, 1939, p. 280). Nevertheless, for the present volume it seems
desirable to augment my earlier review by more liberal citations from
the memoranda Roberts recorded in 1925.

The preponderant pottery from Tests 1 and 2, a total of 25
vertical feet, was an assemblage that seemed to span the years from
Pueblo I to Pueblo II in the Pecos classification (Kidder, 1927) or
from earth-walled pit-houses to those of single-coursed masonry.
Hence the term "Transitional" Roberts and Amsden coined to bridge
the time between. Nearly half of this assemblage was a gray-paste

ware, primarily sherd-tempered and coated with an off-color white slip,
polished before painting. The paint was of mineral origin and black
or sometimes rusty-brown owing to inexpert firing or to insufficient
iron.

Slips varied from thick to thin and were sometimes carelessly
applied; both paint and slip sometimes showed a tendency to chip or
peel—variations I attribute to the misfortunes of production rather
than to intent. Rims were direct, tapered, and painted black; pitchers
were full-bodied and round-bottomed; ladles were of the half-gourd
form until later experimentation turned toward the bowl-and-handle
type. Bowl sherds with polished black interior, although found deep
in the two principal refuse mounds south of the village, occurred in
the uppermost layers only of Test 2. Cook pots were of the smoothbodied,
banded-neck variety—broad to narrow bands, plain or indented
—until followed by all-over Corrugated-coil.

Passing vogues in vessel form and painted decoration are evidenced
from bottom to top in these and other stratified deposits. Squiggled
hachure began early and so did stepped triangles, waved lines, and
free-standing figures. There were transient preferences for designs
composed of broad solid lines, for hachured figures with solid tips,
and others balanced by opposing elements. After this old rubbish pile
had accumulated to a depth of 8 feet, Straight-line Hachure was
introduced, first with widely spaced composing lines within heavy
frames and then with closer bars and lighter framing.

Contemporaneously with Straight-line Hachure and Corrugatedcoil,
or shortly thereafter, our so-called "Chaco-San Juan" type made
its unexpected appearance—a black-on-white variety with a lightgray,
stone-polished slip, tempered chiefly with pulverized potsherds
and ornamented with Mesa Verde-like designs in organic paint. In
thickness and rim treatment, Chaco-San Juan bowls exhibit a compromise
between Mesa Verde and Chaco practices. Instead of being
tapered and painted black in the Chaco tradition, rims are usually
rounded and variously ticked; bowl exteriors are often carelessly
bordered or slap-dashed across the bottom with a full slip-mop.

In Pueblo Bonito stratigraphy this Chaco-San Juan variety appears
earlier and much more abundantly than Mesa Verde Black-on-white,
but, although Roberts and Amsden separated the two while studying
Chaco Canyon pottery in 1925, I admit an inability at this late date to
distinguish one from the other except for individual pieces. Both are
of wide distribution among the mesas and valleys of southeastern
Utah and southwestern Colorado; both are perhaps best described by

Kidder's still useful, but rarely used, term "proto-Mesa Verde"
(Kidder, 1924, p. 67). And I have since come to think of both as
more or less synonymous with McElmo Black-on-white.

Classic Mesa Verde with its thick-walled bowls and flattened rims,
its superb polish, and precisely executed designs, reached Chaco
Canyon just as the high local culture was on the way out. Other late
imports such as Houck, Kayenta, and Chaves Pass polychrome,
Mimbres and Tularosa Coil (Judd, 1921, p. 110), and a few fragments
of Navaho or Apache conical-base pots were also present. A
black-on-red variety, or perhaps two varieties since Amsden and
Roberts divided the lot by color, puzzled us at the time because
sherds from early rubbish included fragments with hachured designs
and ticked rims.

What we called "Mesa Verde," including a few fragments of
undeniable Classic, comprised only 0.4 percent of the 208,188 sherds
Roberts and Amsden tabulated at Pueblo Bonito, while our ChacoSan
Juan group made up 6.6 percent of the total. Of 1,830 potsherds
recovered during excavation of Kiva A, 22.6 percent were Chaco-San
Juan and 10.4 percent Mesa Verde, but, among those from a limited
subfloor test in the same chamber, percentages were 8.1 and 2.7,
respectively. Four Chaco-San Juan sherds among 694 from a subfloor
test pit show that Old Bonitian Room 307 was built later than
others of its kind.

While presenting these and other data gathered within the pueblo
and without, I desire once again to stress the significant fact that
no fragment of Straight-line Hachure, most widely cited element on
Chaco Canyon pottery, was recovered below Layer C, 4 feet 2 inches
from the surface in 12-foot-deep Test 2. This is equally true for
Corrugated-coil Culinary and our Chaco-San Juan variety. Below
Layer C every painted sherd was decorated with a black mineral paint
and most of them were exclusively sherd-tempered. Sherd temper
and mineral paint unite this pottery from the lower 8 feet of Test 2,
the pottery of Old Bonito. Associated culinary vessels were rock- or
sand-tempered, with smooth bodies and banded necks.

There are those who will disagree; but to me it seems obvious
that a typological break occurs at this 8-foot level; that makers of
a different pottery complex came to dwell at Pueblo Bonito after Old
Bonitian household waste had accumulated to a depth of 8 feet or
more. For myself only, the gray-paste, mineral-paint, black-on-white
pottery from that lower 8 feet, the "Transitional," remains a single
ware indistinguishable in composition and ornamentation from the

slaty-gray or grayish-white, sherd-tempered, mineral-paint pottery
known throughout the San Juan country as "Mancos Black-on-white."

Although widely reported and often illustrated, Mancos Black-onwhite
was first described by Martin (1936, pp. 90-94) from Lowry
Ruin, northwest of Mesa Verde National Park, southwestern
Colorado. Subsequent investigations broadened his original description:

Writing from Santa Fe 10 years later, Reed (1958, p. 81) added
to Martin's definition: "Mancos Black-on-white is characterized by
tapered direct rims, unpainted or painted (sometimes smoothly
rounded or nearly squared, sometimes ticked); moderately thin vessel
walls . . . largely unslipped surfaces . . . typically dark bluish gray
. . . but also very often light gray; iron paint; sherd temper"—an
addition that appears to combine Roberts's definitions of the Transitional
and Chaco-San Juan varieties noted at Pueblo Bonito. Of a
collection then in hand Reed wrote (ibid., p. 95): "Fully half the
sample lot of Pueblo III sherds from stratigraphic work in Chaco
Canyon deposited in the Laboratory of Anthropology by Roberts is
solid-style Mancos."

Presumably that sample lot came from one of the two tests Roberts
and Amsden cut through 12 feet of household sweepings under the
West Court at Pueblo Bonito. Because Pueblo Bonito is customarily
thought of as a Pueblo III ruin exclusively, Reed erred in assuming
that every sherd in the sample was dated by the P. III fragments
present. Actually, as I have attempted to emphasize repeatedly,
Roberts and Amsden collected P. III sherds, including those of
Pueblo Bonito's famed cylindrical vases, from the upper 4 feet only.
Any accompanying Transitional, or P. II, fragments merely prove
continuing production of the latter following arrival of P. III
potters.

If the "solid-style Mancos" recognized by Reed in half the sample
lot supplied by Roberts is identical with Mancos Black-on-white, a

diagnostic of Pueblo II civilization all the way across southwestern
Colorado and southeastern Utah, then it was brought to Chaco Canyon
by the immigrating Old Bonitians, a P. II people. There are those
who will disagree, but to me the black-on-white pottery of Old
Bonito has contributed to the Chaco-like resemblances reported from
beyond the San Juan River fully as much as have the three varieties of
Straight-line Hachure and other P. III pottery types of the Late
Bonitians.

Since 1925 a numerous nomenclature has been advanced to identify
every visible difference in Southwestern pottery, including that from
Chaco Canyon. Personally, I find this multiplicity of terms more
confusing than helpful. Those used at Pueblo Bonito by Roberts and
Amsden still seem adequate but other students may prefer other
designations. Each minor variation or error in manufacture does not,
in my opinion, constitute a new variety. Differences in paste composition,
surface finish, or density of pigment may be seen even on opposite
sides of the same vessel, witness the 232 black-on-white
specimens illustrated in "The Material Culture of Pueblo Bonito"
(Judd, 1954).

In 1921, 1922, and again in 1925 our season's plans were discussed
in the field with a chosen company of friends and colleagues skilled in
Southwestern geology, physiology, Indian agriculture, and related
subjects. Only the inadequacies of an archeological camp 95 miles
from a corner grocery limited the number of our guests. Nevertheless,
from impromptu discussions about the evening campfire came
knowledge of Chaco Canyon's past history, its one-time forests, its
prehistoric arroyo, and other factors reflected in the following pages.
A welcome addition to our 1925 company was W. H. Jackson, then
82, whose 1877 survey first focused public attention upon Pueblo
Bonito and its barren surroundings.

We examined Navaho fields to observe the methods practiced by
local Indian farmers. We analyzed soils, flood waters, and well
waters to ascertain their mineral content. Test Pit No. 3, 9 feet
2 inches deep, was situated midway between camp and the ruin (pl.
7, upper). Soil samples taken at 10-inch intervals in that pit showed
an excess of sodium salts (black alkali), top to bottom, that would
have rendered those soils impervious to water. Without water to wet
the soil there would be no crop; without ample harvests a people
dependent upon farming for a livelihood, as the Bonitians were,
could not long survive as a compact, walled-in community.

The ancient forests of Chaco Canyon and the dating of Pueblo

Bonito.—Thousands of pine logs had gone into the roofing of Pueblo
Bonito. We wanted to learn the source of those logs; we hoped to
discover when they were felled. Toward this second objective, the
tree-ring method developed by Dr. A. E. Douglass, then director of
Steward Observatory, University of Arizona, as a means of measuring
the effect of sunspots upon climate and tree growth, seemed
most promising for our purpose. Using materials furnished by the
American Museum of Natural History he had previously correlated
Pueblo Bonito with Aztec Ruin and learned that sections of beams
then in hand showed Pueblo Bonito to be older than Aztec.

In 1922 Dr. Douglass graciously agreed to aid the Society's search,
and I promptly sent him all the wood samples we had recovered from
Pueblo Bonito the year before. But I am reasonably sure that, as he
studied these specimens, his thoughts were focused more upon sunspot
influences than upon the age of Pueblo Bonito. It was 7 years until,
and largely in consequence of the National Geographic Society's
special Beam Expeditions of 1923, 1928, and 1929, he recognized the
feasibility of a tree-ring calendar reaching backward into unrecorded
history (Douglass, 1929, 1935).

At the beginning of our search for the age of Pueblo Bonito
Dr. Douglass, who had been working with the giant redwoods of
California, assured me that any timber less than 6 inches in diameter
was scarcely worth saving. But it was not long thereafter before he
was eagerly scanning every scrap we salvaged—splintered door lintels,
beam borings, and charcoal paraffined and wrapped with twine. I
mention these facts because his early results, published in the National
Geographic Magazine for December 1929, and in the first number
of this series (Douglass, 1935), made the dating of Pueblo Bonito
seem such a simple achievement that few, even among his own students,
realize the discouragements initially encountered and overcome.
Now his method is commonly accepted as a trustworthy guide in
Southwestern archeology, and many minds have lengthened his
original list of dated tree rings (Douglass, 1935).

The 97 specimens from Pueblo Bonito sent to Douglass in 1922
and following, together with the place of origin and his determinations,
are presented hereinafter, but individually they told us more
than their age. They told us that many had been cut in winter or
late autumn; that many had grown where moisture was surprisingly
constant for a region now virtually waterless. Because the individual
specimens were generally from straight-grained timbers, clean,
smooth, and unscarred by transportation it was obvious the trees they

represented had grown at no great distance; had been felled and peeled
while green, and carried by manpower to the building site. But the
forests from which they came are no longer in existence. A dozen
pines, living and dead, stood at the head of Chaco Canyon at the time
of the Society's 1920 reconnaissance; four others, all dead and three
of them fallen, were later seen in Wirito's Rincon, about 2 miles
southeast of Pueblo Bonito (Douglass, 1935, p. 46).

Elderly Navaho told us of pine trees and stumps formerly present
in Mockingbird Canyon and elsewhere. Unknown persons, according
to one informant, had cut the pines on neighboring mesas and their
stumps had been used for fuel by Mexican sheepherders. Always the
sheepherders were to blame! Old Wello, with a steel ax issued at
Fort Defiance before the turn of the century, felled two small pines
on the rimrock at the head of Wirito's Rincon. He wanted them for
repairs to his cabin, built by cattlemen at the north end of Peñasco
Blanco mesa about 1880 and abandoned shortly thereafter. And,
knowing I was from Washington, the old man took particular pains
to assure me he had cut only two of the three pines then standing. A
lone survivor, 5 or 6 inches in diameter, had won anchorage in shallow
soil upon the south cliff overlooking our camp and stood there defiantly
until some needy individual cut it for firewood during the winter of
1926-27 (Douglass, 1935, p. 40).

These scattered remnants, the dead logs in Wirito's rincon, the
stumps in Mockingbird canyon and beyond, the decayed trunk from
the West Court at Pueblo Bonito, the lone survivor on the south cliff,
and the cluster of pines 15 miles to the east are all that remained in
1924 of forests which once crowned the mesas overlooking Chaco
Canyon and extended down through the rincons and out upon the
valley floor.

Whatever their extent or limitations, those ancient forests had
produced thousands of choice timbers, large and small, for Pueblo
Bonito and its neighbors. These timbers grew under diverse conditions
as may be seen from the 97 specimens we recovered. In some
of these, annual growth rings are so uniform as to indicate a nearly
constant water supply year after year; in others, rings are thin,
starved, and stunted. These differences could reflect either a variable
climate or merely unlike growing conditions.

That rainfall was once more plentiful in Chaco Canyon is suggested
not only by growth rings in trees but also by the quantities of reeds
and willows utilized in construction of Pueblo Bonito. Willows and
reeds require moisture, and geologists tell us that ponds or swampy

places capable of nourishing reeds and willows could have been
brought about, prior to erosion of the present arroyo, by only a slight
increase in annual precipitation. Perhaps echoing recollections heard
in boyhood, several of our elderly Navaho neighbors emphatically
insisted that Chaco Canyon was greener "before white men came,"
that grass was then belly-high to a horse, and water could be had anywhere
with a little digging.

These geological opinions and these Navaho recollections lend
credence to the theory of climatic change in the Southwest, as advocated
by Huntington (1914) and others. Paucity of rainfall has long
been considered a principal cause of arroyo formation in the Southwest,
and Douglass (1935, p. 49), with his tree rings before him,
sees a succession of droughts down through the years. There was a
short one about A.D. 920; another, around 980; still another, more
severe and more widespread, between 1090 and 1101. Of our 59
datable timbers from Pueblo Bonito only two were cut during that
decade; only six were felled during the 40-year period of subnormal
rainfall, 1005-1044.

"In the 500-year history of Oraibi even the small droughts were
accompanied by reduced building" (Douglass, 1932, p. 312).
Throughout the long advance of Pueblo civilization, house construction
always declined in times of reduced rainfall (Mindeleff, 1891).
Timbers from old Hopi villages and trees from Arizona forests show
that periods of below-average precipitation recurred irregularly during
the 10th, 11th, and 12th centuries but Pueblo Bonito had been
deserted 100 years or more when the Great Drought of 1276-1299
caused far-reaching devastation throughout the Plateau Province and,
presumably, hastened abandonment of the famous cliff-dwellings of
Mesa Verde National Park.

The prehistoric arroyo.—In 1924 and 1925 Dr. Kirk Bryan, a
geologist with the U. S. Geological Survey and an acknowledged
authority on groundwater resources of the Southwest, undertook in
our behalf a study of sedimentation and erosion in Chaco Canyon.
He examined minutely the banks of the present arroyo, of post-1850
origin, and learned much previously unsuspected of Chaco Canyon
history. He discovered dead campfires and bits of broken pottery
20 feet and more below the surface; he noted that relics of Pueblo III
peoples, the builders of Pueblo Bonito and its kind, occurred in the
upper 4 feet only and those of earlier peoples below that level.

Bryan learned that the main Chaco Canyon fill had been built up
over the centuries by intermittent floodwaters that shifted from place

to place, back and forth, stopped and flowed on, as they deposited
their load of sandy silt and thus annually freshened areas for cultivation.
This silting-up process was a slow one since floodwaters drop
only part of their burden in passing and are lightly turned aside by
a tuft of grass, a clump of greasewood, or a temporary barrier of
wind-borne sand.

Some of that sandy silt was laid down so uniformly by gently flowing
floods as to leave floor-smooth surfaces varying in width from a
few feet to several hundred. Where W. H. Jackson in 1877 noted the
foundations of small P. III ruin "5 or 6 feet below the general level
of the valley" (Jackson, 1878, p. 443), bedded silt previously deposited
extends out on either side, northward to surround Pueblo del
Arroyo and southward across the width of the canyon (Bryan, 1954,
pl. 6, upper). We came upon similar layers beneath the floors of
Pueblo Bonito and farther east, under the abandoned foundations of
a proposed Late Bonitian addition.

In their normal course, wandering floodwaters may erode channels
of greater or less permanence. One such, close under the south walls
of Pueblo Bonito, had persisted year after year despite determined
efforts to dam it with village debris. It had attained a depth of 10
feet and its course had been turned repeatedly toward mid-valley
before the Bonitians won the struggle. It was a forerunner of Chaco
Canyon's destructive 12th-century arroyo which became Kirk
Bryan's primary interest in 1924 and 1925.

Bryan first came upon this prehistoric arroyo near the southeast
corner of Pueblo del Arroyo where Jackson in 1877 had discovered an
earlier exposure 14 feet deep (Bryan, 1954, p. 32). From that
point of discovery Bryan traced the ancient channel up and down
canyon for several miles. Because sand and silt had gradually filled it
to overflowing and continued thereafter to accumulate until its banks
were buried under an additional 4 or 5 feet of alluvium, Bryan soon
came to refer to that prehistoric arroyo as "the buried channel." And
because potsherds found on the bottom of it could be correlated with
the final decades of Pueblo Bonito, he often employed a second
descriptive term, "the post-Bonito channel" (Bryan, 1925, 1926, 1941,
1954).

In his published papers, and especially that of 1954, Bryan reviews
the history of this buried watercourse and discusses its probable
influence upon the occupants of Pueblo Bonito. Where Douglass
blames the builders for decimating the ancient Chaco forests and
thus hastening arroyo formation, Bryan blames the arroyo. It was his

opinion that, by lowering the water table, the buried channel was
chiefly responsible for the denudation of Chaco Canyon and destruction
of Bonitian farmlands.

Chaco Canyon pioneers.—In his study of local geology, Bryan
observed artifacts of the Bonitians and their contemporaries in the
upper 4 feet of the valley fill. Below that level every potsherd was
a product of Early Pueblo (P. I) or Basket Maker peoples. These
were the pioneers of Chaco Canyon! They lived in slab-walled, earthcovered
houses or in single-room pits dug deep into the valley floor,
the roofs supported by four posts.

One such pit-dwelling, on the south side of the canyon opposite
Pueblo Bonito, was partially excavated in 1920 (U.S.N.M. Nos.
315892-901); two years later caving of the arroyo bank a mile to the
east exposed a second pithouse, its floor 12 feet 2 inches below the
present surface (Judd, 1923, p. 136; 1924b, p. 404). After its
abandonment 6 feet of floodwater silt and sand was deposited above
roof level. Charred timbers from this buried home have been dated
A.D. 720 and 777 (Douglass, 1935, p. 44, fn. 1; Smiley, 1951, p. 19);
pottery and other artifacts (U.S.N.M. Nos. 324801-844) are typically
P. I, as Roberts (1938) stated in correcting an earlier misinterpretation.

A third pit-dwelling, its floor at a depth of 13½ feet, had been
half washed away before we discovered it. What remained hung
in the west bank of a narrow gully 9 miles east of Pueblo Bonito
(Judd, 1927, p. 168). On the opposite bank and 13 feet higher, a
small P. III ruin was partially cleared by Frank Roberts that same
summer, 1926, as he tested a nearby BM. III village site for the
Pueblo Bonito Expeditions (Judd, ibid., p. 165). A year later
Roberts completed excavation of this village for the Bureau of American
Ethnology and has so ably reported its distinctive features
(Roberts, 1928, 1929) there is no need herein to review the results
of his 1926 testing. Shabik'eshchee is the only Late Basket Maker
village known in Chaco Canyon, but there may be others.

The surviving portion of that gully bank pit-dwelling was described
by Roberts as "Arroyo House." Under an equally appropriate name,
"Half House," the same remnant was rediscovered and redescribed
by Adams (1951) who postulates two "separate and distinct" occupation
levels, lists 11 types among its potsherds, and cites Deric
O'Bryan's tree-ring dates of A.D. 700-740 for charcoal fragments in
the initial fill. Both Adams and Roberts classify this ancient dwelling
as Basket Maker III but the same evidence could as easily read

Pueblo I. In any case this deep-lying pit-house and the one we cleared
8 miles down valley were both occupied in the 8th century, A.D.

The broken floors of two more BM. III or P. I pit-dwellings were
revealed by our 1925 exploratory trench 11 feet 9 inches below the
West Court surface or approximately 6 feet below the present valley
surface south of Pueblo Bonito (fig. 7). In both instances sandstone
slabs on end, packed between and held upright with mud, marked
floor limit. Another early house remnant, including a 16-inch-high
section of stone-topped adobe wall, was bared on a silt surface 6 feet
3 inches below floor level in Room 241. The builders of Pueblo Bonito
probably were unaware of these and like remains deep beneath their
foundations.