 | The architecture of Pueblo Bonito : |  |
SILT DEPOSITS
In every deliberate test pit, within the ruin or outside, we invariably
came upon one or more of these silt layers. My field notes frequently
refer to them as "pavements" because they were so smooth
and hard as to seem man-made. When more than one was encountered
only the amount of the overlying materials set each apart.
For example, 35 inches under the floor of Room 225 we exposed
the pavementlike surface of a 5-inch-thick adobe stratum with a
slight downward slope to the east and south; beneath it were three
lesser surfaces separated from one another by from 9 to 20 inches
of sand, clay, or occupational debris. A similar, or perhaps the same,
southward-sloping surface was noted 37 inches under the floor of
adjoining Room 241.
Another silt layer 4 inches beneath the northeast steps, East
Refuse Mound (pl. 76, lower), may be a record of the same flood
that deposited a like layer 19 inches below the present surface at
the northeast corner of the West Mound enclosure despite the fact
nothing comparable appeared in the extended East Mound trench
(fig. 24). Although the main valley fill offers no evidence that the
surface gradient ever differed appreciably from what it is today, I
neglected to test this possibility fully. I neglected, for example, to
run a level between the two silt layers last noted or between that under
Station 1, Northeast Foundation Complex, and the silt surface surrounding
Pueblo del Arroyo and underlying at a depth of 5 feet
the small P. III ruin Jackson saw on the opposite bank.
That buried silt layers should appear more clearly defined in some
trenches than in others is understandable, considering the characteristics
of floodwaters and flood-borne silt. That the overburden should
be sand in its infinite variety is obvious, knowing that Chaco Canyon
is bordered by sandstone whose disintegration provided the canyon
floor. Thin clay streaks, gravel lenses, pellets, and chunks of waterwashed
adobe identify in this overburden places where floodwaters
ponded.
As Bryan (1954, p. 25) observed, these pavementlike silt beds
are generally of limited area although an occasional one may extend
a quarter-mile or more. They are the leavings of runoff wandering
laterally from the main flow—silty sand retarded by grassy ground
cover. In lesser measure we noted this same retarding effect at
present-day Navaho fields where a chico bush, a handful of bunchgrass,
or a chance rock sufficed to check or turn the advance of a
muddy rivulet. Unretarded, floodwaters in greater volume might
part of the paths carved by earlier floods. Turning first one way
and then another, such divergent courses were the "discontinuous
channels" of Bryan's Chaco Canyon observations.
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