Recently I did a large file search, for an area spanning southern Wyoming, from Nebraska to Idaho and Utah - an 88 mile wide strip of land along the Colorado line. The study area covers about 81,994 sq km - about the size of the Czech Republic, or, as Tom Wake pointed out to me, slightly smaller than San Bernardino County. I had to develop some custom software for this, in order to be able to automate almost a thousand separate WYCRO searches and combine the results into a single dataset. The final dataset contained some 29,000 prehistoric archaeological sites, which is a nice dataset to work with even if we have only a small amount of information for each site.
Since WYCRO does not support a UTM boundary search option, the search was conducted by Public Land Survey System (PLSS) township and range units, comprising an area from Township 12N to 26N, and Range 60W to 121W: a total of 930 townships. R60W is, of course, on the far eastern edge of the state, and R121W on its extreme western margin. The point of the exercise was to look at archaeological patterning along the east-west axis, and to attempt to identify a zone in which the transition from the Plains to the Wyoming Basin actually took place, culturally speaking.
Here are some of the more interesting results.
The graph represent the number of recorded prehistoric sites along the east-west axis. The horizontal axis represents Range W, with east to the right and west to the left. All of the townships in a particular range were combined to produce a single prehistoric site count for each Range W value. These values are the gray points. The red line is a loess-fitted trend line, a kind of local average, fitted by the loess function of the R statistical package. Obviously, there are a lot more recored archaeological sites in the western part of the study area, from about R85W and westward. For reference, R85W is in the vicinity of Rawlins. This high number of recorded sites in the west is no surprise, since oil and gas development on public lands has been quite intensive in southwestern Wyoming.
The above graph represents the percentage of sites with recorded FCR (fire-cracked rock) or thermal features (hearths) along the east-west axis. The horizontal axis represents Range W, with east to the right and west to the left. All of the townships in a particular range were combined to produce a single percentage for each Range W value. FCR and thermal features are much more common in the western portion of the transect. This could in part reflect lifeway differences, with more processing of marginal resources such as tubers in the Wyoming Basin as opposed to hunting on the Plains. It could also reflect the generally higher surface visibility in the drier western portion of the transect.
FCR and thermal features are relatively common, with a mean per-Range frequency of 50.2%, with a maximum frequency of 85.9% and a minimum of 10.3%. The loess-fitted trend line suggests that FCR and thermal features are very common (>40% frequency) to the west of approximately R80W, and somewhat less common (<40% frequency) to the east of that line. The zone from R80-90W appears to be a transition zone, in which FCR and thermal feature frequency declines regularly from west to east. The pattern observed in FCR and thermal feature frequency is complementary to the observed pattern of stone circle frequency (below), with high FCR/thermal feature frequency corresponding to low stone circle frequency, and vice versa.
The above graph shows the percentage of sites with stone circle features along the east-west transect. Stone circles are considerably more common in the East, supporting their association with Plains cultures.
Stone circles are relatively common, with a mean per-Range frequency of 7.1%, with a maximum frequency of 37.7% and a minimum of 0%. The loess-fitted trend line suggests that stone circles are very common (>10% frequency) to the east of approximately R90W, and much less common (<5% frequency) to the west of that line. The zone from R80-90W appears to be a transition zone, in which stone circle frequency declines regularly from east to west. The high variance in stone circle frequency in the eastern portion of the study area likely reflects the effect of small samples in some Ranges. The change in stone circle frequency is the most robust pattern observed in the dataset.
The mean per-Range frequency of Stone cairns and alignments (above) is 4.4%, with a maximum of 35.8% and a minimum of 0%. In general, areas to the west of R90W fall below this level, while areas to the east of R90W fall above it. Cairns and alignments, therefore, appear to be more common in the eastern portion of the study area. While some of the high values in the eastern area are no doubt the result of sample effects, the overall patterns appears to be robust.
Finally, ceramics (above) are much more common in the East than in the West. Areas to the west of R80W seem to have low ceramic frequencies (<1%),while areas further to the east seem to have higher ceramics frequencies (>1%), though the eastern area of course has a high variance as would be expected given its small sample sizes.
On the whole then, we get a fairly clear picture of two cultural traditions, one associated with stone circles, cairns, alignments, and ceramics (Plains), and the other associated with FCR and thermal features (Wyoming Basin). These two traditions intersect somewhere in the vicinity of Rawlins, which, unsurprisingly, is also located along the ecotone between the wetter eastern grasslands and the scrub desert of southwestern Wyoming.
Since the aggregate radiocarbon record, which I will discuss in another post, show that the archaeological record of southern Wyoming is dominated by Late Prehistoric sites, this difference is probably produced mainly by human habitation within the last two millennia. Whether such a cultural divide existed in the Archaic period remains an open question, one that cannot be addressed with the sort of coarse-grained data that I have used here.
In a later post I will present some statistical analysis of these data that further strengthen the notion that there is a clear division between the archaeological record of southwestern and southeastern Wyoming.