University of Virginia Library

ANCIENT FORESTS

Dr. A. E. Douglass (1935) has recounted our search for traces
of the forests that furnished timbers for construction of Pueblo
Bonito. Fifteen or sixteen miles east of the ruin a couple of dozen pine
trees, living and dead, comprised the largest surviving remnant of
those forests. Four dead pines, one of them still standing (pl. 2, left),
were seen at the head of Wirito's Rincon, 2 miles or more southeast
of Bonito. A lone survivor, on the south mesa and within sight of
our camp, was cut for firewood during the winter of 1926-27.

Thousands of logs went into the roofs and ceilings of Pueblo
Bonito. Fragments unearthed during the course of our excavations
were invariably straight-grained, clean, and smooth. They had been
felled and peeled while green; they showed no scars of transportation.

Clearly they were cut within easy carrying distance. The
character of their annual rings shows that most of them grew under
exceptionally favorable conditions. Thanks to a technique developed
by Dr. Douglass, the age of pine and fir beams can ordinarily be determined
from their growth rings, but fully 10 percent of the samples
we collected are useless for that purpose because their rings are too
uniform in thickness. Such regularity indicates an abundant, constant
water supply. Obviously Chaco Canyon had more rainfall when those
beams were living trees.

Old Navahos told us of pines and pine stumps formerly standing
in Mockingbird Canyon and elsewhere. We found some but not all.
At the south end of the West Court we unexpectedly discovered the
remains of a large pine that had stood there, alive and green, when
Pueblo Bonito was inhabited. Its decayed trunk lay on the last
utilized pavement, and its great, snaglike roots preclude the possibility
of its ever having been moved (pl. 2, right). Unfortunately the outer
part had rotted away, and so we could not learn the year the tree
died. Its last readable ring gave A.D. 1017, but there was an unknown
number missing after that. Altogether, our observations indicate the
former existence of a pine forest in close proximity to Pueblo Bonito,
principally on the south mesa but with fringes reaching down into
the rincons and even out upon the valley floor.

Man and nature joined in the dissipation of the Chaco forests. Man
felled the trees; without trees to check runoff following passing
storms, the shallow soil was gradually washed from the underlying
sandstone. Floodwaters drained even more quickly from bare rock
and poured down into the valley. In a surprisingly short time the
alluvial fill of the canyon was being trenched by an animated gully.
Year after year that gully grew in width and depth as it cut its way
upstream. In consequence, the water table was soon lowered beyond
reach of grass, trees, and shrubs. As the ground cover withered and
died the rapidity of runoff was accelerated. When floodwaters could
no longer be controlled, fields they had previously watered were useless.
Without bountiful crops, communal life on the scale practiced
at Pueblo Bonito became impossible. Family groups withdrew to seek
their fortune elsewhere; eventually none was left.

The channel that may well have been a determining factor in compelling
abandonment of Pueblo Bonito has its present-day counterpart.
We watched this latter as it annually carved a deeper course and
reached out hungrily on either side. Every passing flood took its toll.
In a single season, that of 1923, storm waters debouching from
Wirito's Rincon, a mile and a half upcanyon, left a wide fan of sand

and gravel that completely blocked our road to Crownpoint and
Thoreau. Successive floods uprooted the windmill on an arroyo bar
west of Una Vida and gnawed at the talus under the nearby cliff.

There was an arroyo of sorts here in 1849. It was probably intermittent
and, for the most part, inconspicuous. We draw this inference
from the journal of Lt. James H. Simpson, a member of the military
expedition under Lt. Col. John M. Washington that passed through
upper Chaco Canyon that year. After breaking camp on the morning
of August 28 the main body of troops left the canyon at Fajada
Butte while Simpson and nine companions went on to see reported
ruins. His journal makes no reference whatever to a gully, but when
the little party stopped briefly at the ruin next below Pueblo Bonito
his Mexican guide had a name on tongue's tip: "Pueblo of the
Arroyo" (Simpson, 1850, p. 81).

During a day crowded with the excitement of inspecting what few
white men had previously seen and none had described, six major
Chaco Canyon ruins and sundry smaller ones, it is conceivable that
Simpson overlooked so commonplace a subject as an arroyo. On the
other hand, he mentions none between August 25, when the troops
were on the east crest of the Continental Divide, and September 1,
when they began their ascent of the Tunicha Mountains.

Where Colonel Washington's command camped for the night of
August 27, 1849, less than 2 miles west of Pueblo Wejegi, Simpson
(ibid., p. 78) reported that "the Rio Chaco . . . has a width of eight
feet, and a depth of one and a half. Its waters . . . are of a rich clay
color." Twenty-four hours later and about 23 miles farther west,
he added: "The water of the Rio Chaco has been gradually increasing
in volume in proportion as we descended" (ibid., p. 86). He had
passed the Escavada and several lesser tributaries. Twenty-three
miles of running water can only mean that rains had crossed the
upper Chaco drainage a few days earlier and, as may happen, had
somehow missed the expedition. Late August is within the normal
rainy season.

In 1877, 28 years after Simpson, W. H. Jackson, famed photographer
of the Hayden Surveys, found Chaco Canyon gutted from
end to end by a channel 10 feet deep or more. It was 10 or 12 feet
deep at Pueblo Pintado; 16 at Pueblo del Arroyo (Jackson, 1878,
pp. 433, 443).

Our oldest Navaho neighbors (pl. 3) professed to remember when
there was little or no gully in Chaco Canyon; when water could be had
anywhere with a little digging; when a ribbon of cottonwoods and
willows marked the middle of the valley, and grass grew thick and tall.

Fig. 1-The central portion of Chaco Canyon, New Mexico
scene of the National Geographic Society's
archeological investigations.

Hosteen Beyal stated emphatically that there was no arroyo above
the mouth of Escavada Wash when he was a boy. On the contrary,
the canyon was then carpeted with high grass among which shallow
pools of rainwater stood throughout the year. He recalls neither
cottonwoods nor willows opposite Pueblo Bonito but says both were
numerous downcanyon, nearer Peñasco Blanco, and still more plentiful
beyond.

By his son's estimate, Hosteen Beyal was born about 1832 and first
saw Chaco Canyon 10 years later. Thus his boyhood recollections
were of a time shortly antedating Simpson's recorded observations of
1849. Where Simpson found an arroyo just prominent enough to
suggest a name for the ruin nearest Pueblo Bonito, Jackson, 28 years
later, encountered one 16 feet deep and 40 to 60 feet wide.

Intrenchment of the Chaco was therefore already accomplished
when cattle were locally introduced on a large scale, in 1878 or 1879.
The livestock industry may be blameworthy elsewhere but not here.
Jackson, reporting his 1877 observations, mentions neither cattle nor
cattlemen. Yet within 2 years thereafter, two large companies, the
"LC's" and the Carlisles, had moved in and usurped nearly all the
range between the present Crownpoint area and the San Juan. It
was probably the former, owned by a Dr. Lacy, that in 1879 built
the stone houses under the cliff north of Peñasco Blanco for ranch
headquarters (information from John Wetherill, 1936). I have not
learned when or why they abandoned the Chaco country, but both
companies had moved into southeastern Utah before 1896. And Old
Wello had promptly appropriated to himself the vacated "LC" buildings
and continued to occupy them until his death, in 1926.

The existing Chaco arroyo is at least the third of its kind, according
to Bryan (1941). His physiographic studies in our behalf (Bryan,
1954) show that here, as in several other localities examined, floodwaters
have alternately deposited vast quantities of alluvium and
later bisected those deposits with gullies similar to recent arroyos.
Presumably another cycle of alluviation will follow the current period
of erosion. These phenomena are most readily explained, in Bryan's
opinion, by the theory of climatic change, a theory first proposed by
Huntington (1914).

The theory of a changing climate assumes that floodwaters are
largely regulated by vegetation. A conspicuous change in temperature
or rainfall is not essential, merely a slight shift from the dry toward
the less dry. We have ample proof of such shifts. Although our
Navaho informants, relying upon memories of their boyhood, insisted
that he exaggerated, Simpson pictured a rather sparse ground cover

when he rode through Chaco Canyon in 1849, at the inception of the
present arroyo system. On the other hand, the rushes with which
Bonitian wives wove their sleeping mats and the pine logs that roofed
their dwellings alike evidence moister conditions when Pueblo Bonito
was inhabited, 800 years before. Here and elsewhere throughout
the plateau country growth rings in timbers from prehistoric ruins
provide a visible record of recurrent periods of deficient rainfall in
times past. The Great Drought of 1276-99 merely climaxed a long
succession of lesser droughts (Douglass, 1935, p. 49). Since the
protection normally provided by living plants is lessened by any reduction
in their density, erosion naturally follows periods of diminished
rainfall. Thus the theory of climatic change seems to offer the
most plausible explanation for the alternating periods of erosion and
sedimentation Bryan sees in the alluvial fill of Chaco Canyon.