The two levels represented in the section from M11 extend over the
whole area of excavation and make up most of the deposits of the
site. A late Pleistocene bouldery gravel, with which is included some
variegated silty and clayey alluvium, is separated from the overlying
dark-colored sandy and silty “alluvium” by a definite erosional break
representing an unknown interval of time (Hunt, this report). There is
a higher red sand layer and a younger bed of dusty brown fill which is
found just below the surface; both of these are relatively quite thin
and extend only over part of the area of the site. As the dark-colored
homogeneous sands and silts made up most of the deposits of the site,
and contained most of the cultural remains, they will be our particular
concern.
The results of sieve analyses made on the samples from the front and
back of the site have been summarized in Tables VIa and VIb; the
breakdown into the various particle size fractions is by weight. This
was done to 1) describe the physical nature of the deposits and 2) to
determine the nature of textural variation of the samples.
[Illustration]
[Illustration: FIGURE 67—Above: Size-distribution curves for typical
samples of the deposits of the LoDaisKa Site, Square M11.
Below: Size-distribution Curves for typical samples of the deposits of
the LoDaisKa Site, Square J8.]
Local differences and variations in the parent rock and relief have a
profound effect on soil characteristics (Thorp, 1941). In the present
instance, there is no evidence of any appreciable change in the relief
of the area immediately surrounding the site since the beginning of
human occupation. The site is located towards one end of the relatively
steep slope of outwash debris from the Fountain Formation which forms
the overhang and extends upslope above the site. The deposits which
make up the site are also the product of slope wash and of weathering
of the overhang; they are some six feet above the level of the stream
in Strain Gulch. The height of the deposits above modern stream level
makes it seem most unlikely that the site was ever flooded in Recent
times (Hunt, personal communication—Irwin and Irwin). Accordingly, the
deposits would be a colluvium rather than alluvial in nature and would
be derived from the overhang. Mechanical analyses of several samples of
the Fountain Sandstone from the overhang suggest that the sandstone as
it is found above the site is quite homogeneous, although it varies in
color from white to maroon (see pg. 99 of this report):
Diameter in mm. Percent by weight
2.00 19.33%
2.00-1.00 16.51%
1.00-0.71 8.64%
0.71-0.50 8.33%
0.50-0.351 8.61%
0.351-0.25 8.89%
0.25-0.177 5.51%
0.177-0.125 5.68%
0.125-0.088 4.69%
0.088-0.062 3.37%
0.062 10.40%
------
99.96%
These results compare closely with the analyses of the deposits making
up the site, and suggest that weathering of the parent material
was primarily dissolution, probably accompanied by some mechanical
disintegration.
[Illustration]
[Illustration]
[Illustration: FIGURE 68—Above: Changes in relative importance (weight
percent) of fine silt and clay fraction with depth below 38 inches
below baseline, LoDaisKa site.
Center: Changes in concentration of total calcium carbonate with depth
below 38 inches below baseline, LoDaisKa site.
Below: Changes in concentration of total soluble iron with depth below
38 inches below baseline, LoDaisKa site.]
Representative particle size distributions of the deposits are shown
in the cumulative curves in Fig. 67. The median diameters and sorting
coefficients, as we have already noted, suggest a uniform distribution
of particle sizes, with the exception of the sample (W3) from depth
52-58 inches below baseline in front of the site. The median diameter
of this sample is 1.32 mm., considerably larger than that (0.60-0.70
mm.) for the rest of the deposits. A line of much larger rocks at
this level gives evidence of a period of rock fall, although this
does not seem to extend to the very back of the shelter, and is not
represented in the sample collected there. The human occupation of
the site is uninterrupted, and there is no suggestion that this fall
reflects any change in the mode of deposition or any change in climate.
Increased aridity may have brought about an important increase in
aeolian deposition in the area during some period of occupation, but
the location of the site in a sheltered valley makes it unlikely that
this would be indicated by the deposits. Any significant change in the
relative importance of the coarse and fine fractions—suggesting perhaps
such a change in deposition—would be reflected in the median diameters
of the samples (Jenny, 1941). The similarity in the median diameters of
the particles from the deposit gives evidence of a relatively uniform
mode of deposition.
The amount of uncombined carbonate and “free” or acid-soluble iron
oxide in the clay and silt fraction (finer than 0.062 mm.) of the
samples from the back of the shelter (M11) was determined by chemical
analysis. The results of these analyses have been summarized in Fig.
68, where the percentage of the fines by weight has also been plotted.
The uncombined oxides and carbonates (iron oxide and calcium carbonate)
are present in the fine fractions especially in the form of an adsorbed
coating on the surfaces of the particles, and also as precipitates
acting as cementing materials to bind them together (Carroll, 1958;
Deb, 1958; Barshad, 1958). The free iron oxides were obtained by
dissolving the sample in 10% HC₁ (by volume) and digestion over a
steam bath. It is assumed that any dissolution of the clay minerals is
insignificant and that the amount of soluble iron determined is truly
representative of the uncombined iron oxide in the sample (Barshad,
1958). The amount of carbonate was determined in the form of CO₂,
by digesting the sample in 0.1N HCl; it is assumed that all of the
carbonate occurred in the form of calcium carbonate.
A carbonate and iron oxide analysis was run on several samples of the
Fountain sandstone which made up the roof of the rockshelter, in order
to determine the amount of variation in the parent material:
Sample Percent Carbonate Percent Iron
(by weight) (by weight)
sol. insol. total
Light
No. 1 0.34% 0.43% 0.14% 0.57%
No. 2 0.31% 0.38% 0.13% 0.51%
Red
No. 1 0.08% 4.95% 0.62% 5.57%
The amount of soluble iron is quite variable in the parent material; it
forms a coating on the primary minerals and gives the rock its red or
maroon color. It is interesting to note that the soluble iron in the
deposits, presumably derived from the Fountain sandstone, maintains a
rather regular increase to a maximum at 102 inches below base-level.
The amount of carbonate in the parent rock, by contrast, is certainly
not enough to account for the variation which was found in the deposits
and for the concentration of CaCO₃ at the particular levels. In the
present instance there seems to be a definite independence in the
movement and location of concentration of the soluble iron and of the
fine silt and clay, which seem to be associated with concentrations of
carbonate. The calcium carbonate occurs in the form of a coating on the
fine particles and, more important, as a cement binding the particles
together. This was particularly noticed on the artifactual and bone
materials from the deposits from 70 to 94 inches below baseline.
The differential accumulation of calcium carbonate in the profile is
due to either variations in the texture of the deposits, with the
greater accumulations occurring in the zones of finer particle size,
or to the processes of weathering of the deposits (Miller and Leopold,
1953). The present study suggests that changes in the distribution of
calcium carbonate and the fine silt and clay fractions in the deposits
cannot be related to variations in the parent material, relief in the
immediate area, or the mode of deposition. Concentrations of calcium
carbonate may be associated with changes in the depth of the water
table or in drainage conditions. There is no evidence that the water
table ever came close to the surface in this area in Recent times; at
present it is something more than 150 feet below the level of the site.
Internal and external drainage conditions of the deposits have probably
not changed since the beginning of human occupation of the shelter,
being largely determined by the nature of the relief and parent rock.
It is possible that the particular accumulation of calcium carbonate
and of fine silt and clay between 68 and 96 inches below base-level
are the result of downward migration and concentration of the fine
fraction and CaCO₃ due to weathering processes—defining a paleosol.
Some change in climatic conditions, perhaps just sufficient to modify
to some extent the nature of the vegetation cover (Nikiforoff, 1937)
seems to offer one logical explanation for the distribution of calcium
carbonate, and of the fine silt and clay fraction—the products of soil
development in semi-arid environments (Bryan and Albritton, 1943). It
is hoped that x-ray and mineralogical analysis of the samples will
definitely establish whether or not we are dealing with a buried soil.
If we do interpret the results of the chemical analyses as indicating a
period of increased aridity over conditions as they now exist in the
area, one could establish a _terminus post quem_ for the archaeological
complexes below approximately 64 inches below baseline. Accordingly,
the artifactual materials with Great Basin influences and the earlier
Duncan types may date from some time late in the Altithermal. This
interpretation would not be completely out of keeping with a dating of
the archaeological materials on typological grounds.