8 June
1997
Obsidian Studies at CA-SOL-356
These analyses
showed that obsidian use at this site occurred during the Upper Archaic and
Emergent Periods in
Virtually all
obsidian was visually identified as
Results of
these studies indicate three dominant technological strategies for tool
production during the Emergent Period. The primary mode of reduction centered
on use of locally obtained cobbles but supplies might have been supplemented by
similar raw materials acquired through either direct quarry access in or near
the
As noted
above, virtually all obsidian items examined were assignable to the
Previous
studies of cultural obsidian recovered in the
With respect
to addressing the research questions, several data sets were primary among
those selected for hydration testing.
(1) Small
serrated projectile points with expanding bases.
(2) Small
serrated projectile points with straight stems and basal fragments from these
types.
(3) Non-serrated
projectile points.
(4) Ventral
face flakes (with or without dorsal patination) -
among the first flakes detached from the ventral face of a larger flake
blank/core having a remnant of that unmodified surface on the dorsal face.
(5) Small
triangular or teardrop shape bifaces and
edge-modified flakes (Type 4), some with preliminary notches at a break,
presumed to represent either point blanks or preforms
for the small serrated forms recovered.
(6) Interior
flakes with and without dorsal patination.
(7) Other bifaces and tool forms.
Applying the
current aspect of this study to the research questions, many of the items
selected for hydration were marked to indicate the placement of the cut. The
test cut locations included combinations of unmodified ventral surfaces,
seemingly unmodified dorsal surfaces, dorsal areas with differential patination, and or fracture faces (see below). Some
unmarked items were submitted to the hydration laboratory at
One
hundred-three items were submitted for hydration testing. Ninety-one items
returned hydration band values; fourteen yielded multiple bands. The remainder
had either diffuse or weathered rims or lacked visible bands. In several
instances, second bands of variable width or diffuse fronts were recognized.
The hydration technician also commented on the nature of several extensively
weathered surfaces that could be attributable to exposure to intense heat.
Most of the
hydration values classed as Band 1 identified obsidian use during the Emergent
Period whether adjusted for temperature or not. Adjusted values exhibited three
modal peaks during the hydration span attributed to the Emergent Period--at
about 1.1 microns, 1.8 microns, and 2.1 microns. The non-adjusted values also
show three hydration band groups but the clusters are more diffuse. Several
other adjusted hydration bands were associated with Middle and Upper Archaic
Period use. One primary band and two secondary bands could represent much
earlier cultural use of the area while at least two other second bands were
probably obtained from non-cultural surfaces on the artifact.
A number of
items were submitted for hydration testing to evaluate aspects of technological
history through the potential identification of multiple bands. One of these
data sets included twelve pieces of debitage
consisting of four ventral face flakes (three which were also EMFs) and eight un-modified items, all with dorsal patination. Of these, three of the pieces of un-modified debitage and two of the EMFs
yielded second bands. Four of the bands were between 4.1 microns and 6.5
microns while one was approximately 14.8 microns; although it was very small,
the latter appeared to have been a non-cultural surface area. One other piece
of debitage without a distinct patinated
dorsal surface yielded a second band off its platform.
In addition,
as many as 51 artifacts (mostly small serrated projectile points) characterized
by remnants of original ventral and/or dorsal surfaces were submitted. Of
these, 10 yielded second bands. Most second bands from these items were between
1.8 microns and 8.9 microns, adjusted. Two others that yielded 10.8 microns and
13.0 microns (adjusted) were suspected of having tested non-cultural surfaces.
All items yielding multiple bands were visually assigned to the
Seven
Hydration
analysis pertaining to typological studies revealed most forms were not
temporally well-separated. This could be attributed to cultural or
environmental factors affecting hydration band formation or resolution limits
of optical microscopy used by technicians (Stevenson, et al. 1989). Some
patterns recognized in other studies, however, were supported.
Non-serrated
corner-notched forms tended to be later in time than most serrated types.
Specifically, types 5A (n=2) and a fragment assumed to be a type 5 had smaller
hydration bands than most type 2s and 3s. Five Type 3s had a mean hydration
value larger than nine Type 2As, six possible 2As, and five Type 2Vs. Although
five 2Bs showed a larger mean, four of the items had 2.0 microns or smaller
bands. Two Type 3V were characterized by mean values
that might support their association with Type 1 items.
All obsidian debitage recovered from units 1, 2, 3, and 8 were included
in a technological study. Selection of these units for the study was predicated
on location, depth range, recovery rate, and recovery strategy. Units 1 and 3
were sampled in the field by 3mm screen while the other two units were subject
to 6mm recovery. Recovery rates for these units were in the higher ranges for
units excavated below 70cm. Units 2, 3, and 8 were situated within the central
area of the site while Unit 1 was more than 30m northwest of that area.
Given the research
objectives and certain expectations about Late Period technological
organization derived from previous investigations, classification focused on
attributes deemed most useful for assessing the importance of early reduction
and manufacture stages. Diagnostic flake types identified for this study
included ventral face flakes (VFF), flakes with bifacial platforms (BIE),
flakes with bifacial distal edges (i.e., overshots;
BIO), notching flakes (NOT), and impact flakes (IMP). All these flake types
were also counted and weighed separately when they were identified in the debitage samples of other units during the cataloging
phase; this supporting information will be addressed below. All other flakes
and fragments were grouped as "general"; these included a variety of
pressure flakes, thinning flakes, alternate flakes, miscellaneous fragments,
and other diagnostic and non-diagnostic elements. Each category was counted,
weighed, and the presence of cortex or dorsal patination
was recorded.
In all, the
sample was comprised of 2,136 pieces. Cortex was present on 522 items (24%)
defined by a mean weight of 0.59 grams. Items with dorsal patination
accounted for less than 4% (n=85) and had a mean weight of 0.40 grams.
Non-cortical non-patinated pieces accounted for
almost 72% (n=1529) with a mean weight of 0.24 grams. Flakes directly
attributable to biface manufacture and repair (BIE,
BIO, and NOT) accounted for less than 2% of the sample (n=32). Flakes with
bifacial edges comprised 1% of the sample (n=30). If thinning flakes and
late-stage pressure flakes were included in an assessment of the relative
importance of biface reduction, it is still unlikely
the proportion would be considered significant.
The percentage
of items retaining cortex was most consistent in units 2, 3, and 8, where the
proportion ranged from 20% to 29%. Likewise, mean weights for cortical debitage in these units ranged from 0.61 g to 0.64 grams.
On the other hand, the sample from Unit 1 contained 13% cortical material
marked by a mean weight of 0.32 grams. The greatest differences in mean weight
were evident in the 3mm recovery units, 1 and 3.
In contrast,
non-cortical non-patinated materials from units 1 and
3 were smaller on average than those from the 6mm units, 2 and 8, as would be
expected. In the former units, the mean weights for these categories were 0.13
g and 0.18 g, whereas in the latter 6mm units the values were 0.29 g and 0.31
grams. Ventral face flakes comprised a greater proportion of the debitage assemblage in units 2 (7%), 3 (5%), and 8 (8%)
than they did in Unit 1 (3%) but hardly to a significant degree. Given the
proportions of cortical materials and VFFs, it is
concluded activities at the Unit 1 location included less primary reduction
than the core site area.
Debitage from units other than those used in the technological
analysis was also examined for ventral face flakes. On average, these flakes
accounted for 3-11% of the obsidian debitage
recovered from those units. The frequency of ventral face flakes in either the
units selected for technological analyses or the non-sampled units does not
differ significantly.
Twenty-six
additional BIE flakes, three BIO, one NOT, three IMP,
and a possible uniface rejuvenation flake were
identified in the non-sampled units (units 6, 7, 7E, 7EN, 7ES, 7W and 8). Two
of the BIOs were classed as early-stage and the other
was defined as middle-stage. BIEs had a mean weight
of 0.47 g, virtually the same as defined for the sampled BIEs.
Although not
quantified, cortex on items varied. On some pieces cortex was coarse but
weathered; some pieces had coarse, grey, unweathered
cortex; while other pieces were marked by weathered surfaces lacking evidence
of conchoidal fracture. The first of these groups was
assumed to derive mostly from surrounding hills and drainages. The group with
coarse grey cortex resembled material at the
Several
recently investigated prehistoric sites were situated within about three miles
of SOL-356. Two of these, SOL-315 and SOL-355/H, were also the subject of
obsidian studies by Holman & Associates. SOL-315 and SOL-355/H were Archaic
Period sites situated within one mile of SOL-356. SOL-315 was used throughout
the Archaic Period, whereas SOL-355/H was an occupation site used almost
exclusively during the Upper Archaic. Obsidian assemblages recovered from these
two sites exemplify diverse strategies of technological organization and in
some respects contrast sharply with those identified at SOL-356.
Recovery rates
of obsidian materials were highest at SOL-315 while debitage
mean weights were lowest, whereas SOL-355/H yielded the lowest number per cubic
meter but higher mean weights. High recovery rates and small sizes of debitage and tools at SOL-315 were attributed to (1)
potentially intensive use throughout an extended time period within a spatially
restricted area; and (2) curation of volcanic glass
materials (Bieling 1992). Conversely, higher mean
weights of debitage at SOL-355/H were attributed to a
reduction strategy characterized in part by more middle-stage tool production
and less curation (Bieling
1993). A briefer occupation span at the latter could account for lower recovery
rates.
Although
higher recovery rates at SOL-356 could be partially attributed to occupation
span, a technological strategy emphasizing production of small points and
somewhat larger biface forms from cobbles was
probably responsible for contributing greater amounts of material in a
concentrated area. Debitage mean weights were more
than 50% greater than those at SOL-315.
Other factors contributing
to these differences are quantities and sizes of flake tools and their implied
functions. As noted above, tools at SOL-315 were generally small and it was
unlikely many of the modified flakes were part of a biface
manufacturing trajectory. The reverse appears to be the case at SOL-356.
Modified flakes (those not reclassified as blanks) were still characterized by
higher average weights and a greater size range than those at SOL-315 or
SOL-355/H (the sole exception was a single formally shaped scraper at
SOL-355/H). Ninety-seven percent of the EMFs and 87%
of the RTFs weighed less than 4.0 g; 80% of the EMFs were less than 2.0 grams. Although many had been
re-classified as items comprising part of a manufacturing trajectory geared
towards small points, other less diagnostic items within the EMF and RTF
categories could represent fragments of broken blanks, and could thus be
contributing to higher mean weights reflected in larger standard deviations.
Discussion
Obsidian
source and technological studies and hydration results on selected items
provide information about material procurement. Multiple hydration bands on
particular items, a relatively high proportion of debitage
retaining cortex coupled with the additional items marked by dorsal patination support a strategy characterized by three
methods of procurement: (1) naturally occurring cobbles were obtained from
nearby stream beds and hillslopes where the materials
eroded out of the Sonoma Volcanics geologic unit (Fox
1983; Fox, et al. 1985); (2) pieces of raw material was obtained either
directly from quarry workshops in the Napa Valley region or through exchange
with people to the west; and (3) previously worked material--possibly from
nearby sites--was acquired directly or indirectly, or both. Of these
strategies, the foregoing analyses indicate procurement of local un-modified
materials probably represented the greatest contribution to the site deposit
and might have been the dominant mode during the Emergent Period.
The amount of
items retaining cortex plus the high number of ventral face flakes and
early-stage examples of small point forms indicate a technological pattern
characterized strongly by local procurement of raw material and on-site tool
production. Tool manufacture was overwhelming represented by production of
small serrated projectile points, from the flake blank stage to final form. A
number of larger, early- and middle-stage biface
forms could represent either the production of formal tools or preparation of
bifacial core forms. Another dominant element of the flaked-stone toolkit were used flakes. Although many could be recognized as
potential flake blanks, many others were too small, had irregular edges, or
wear patterns inconsistent with blank shaping.
Conclusions
Studies of the
collection from SOL-356 have shown Emergent Period obsidian use at this site
was characterized in large part by the production of small serrated projectile
points and simple flake tools from locally obtained cobbles. Various biface forms and cores were also produced. Temporal ranges
for selected artifact types were presented above and appear consistent with
findings by other researchers in spite of expectations; factors affecting
hydration bands development and alteration, however, can not be ruled out. Specifically,
hydration data derived from small serrated projectile points compared favorably
with results from ALA-555 and the NCR studies by Fredrickson and Origer (1995). Finer resolution of the temporal
relationships of the types defined will have to await further investigations
with larger samples.
Compared to
cumulative hydration data from the Napa Region, the
Initial use of
SOL-356 occurred during the Archaic Period. Given the absence of a larger number
of temporally diagnostic artifacts, this use might have been of a task specific
nature, such as hunting or fishing, by peoples occupying other sites within
Site use
during the Emergent Period was marked by increased obsidian working and might
represent a growing population, as well. Greater amounts of obsidian were
recovered in upper excavation levels and late Phase 1/early Phase 2 point types
were the most represented temporally diagnostic forms. It must be noted,
however, that certain manufacturing trajectories can be responsible for the
production of large amounts of debris and byproducts and should not be directly
correlated with increases in populations.
A shift in
reduction strategies from somewhat thicker, fully bifacial, parallel
sided-stemmed serrated points to thinner serrated forms with expanding bases
more often made on flakes was identified. Earlier reduction stages for the
parallel-sided stemmed forms was not identified during these studies, however,
some triangular bifacial blanks could be attributed to this trajectory on the
basis of hydration results. A more robust manufacturing assemblage was defined
for the later serrated point forms.
Certain
reduction objectives of the people at SOL-356 were virtually identical to those
of people at ALA-555--an archaeological site near
The presence
of second hydration bands on several items has been interpreted as the product
of recycling of scavenged cultural materials and use of non-local raw
materials. Similar explanations have been posited to explain certain elements
of assemblages with second bands from the
Social
distance between the people occupying SOL-356 and those of the surrounding
region can be addressed through the quantification of obsidian types and the
forms in which they were found. The present studies showed that
The preceding
analysis has examined a number of aspects of cultural systems in the
References Cited
· Bieling, D. G.
1992 Analysis of Obsidian Materials Recovered from CA-SOL-69 and CA-SOL-315.
In, Archaeological Data Recovery at Sites CA-SOL-69 and
CA-SOL-315,
1993 Analysis of Obsidian from CA-SOL-355/H,
· Fox, K. F.
1983 Tectonic Setting of Late Miocene, Pliocene, and Pleistocene Rocks in Part
of the
· Fox, K. F., Jr., R. J. Fleck, G. H.
Curtis, and C. E. Meyer
1985 Potassium-Argon and Fission-Track Ages of the Sonoma Volcanics
in an Area North of San Pablo Bay, California. United States Geological Survey
Miscellaneous Field Studies Map 1753.
·
Fredrickson, D. A. and T. Origer
1995 Temporally Sensitive Attributes of Late Period Serrated Arrow Points in
· Skinner, E.
1988 Scavenging and Reuse: An Alternative to Models of Late Prehistoric
Trans-Sierran Exchange in
· Stevenson, C. M., D. Dinsmore, and B. E. Scheetz
1989 An Inter-Laboratory Comparison of Hydration Rind Measurements.
International Association for Obsidian Studies Newsletter 1:7-13.
· Tremaine, K. J.
1989 Obsidian as a Time Keeper: An Investigation in Absolute and Relative
Dating. Master's Thesis, Department of Anthropology,
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