This week I received radiocarbon dating results from two samples I submitted to Beta Analytic. Radiocarbon dates are not cheap (about $600 for an AMS analysis that returns an age estimate from a very small sample), and I am grateful to a private donor who supplied funds to date one of the samples from 38FA608.
Here are the date results on a generalized figure of the stratigraphy at 38FA608 as I currently understand it (based on profiles of Units 1, 2, 9, 11, and the original machine cut):
The date for the Zone 19 sample, however . . . was a bit of a surprise. It also came back as Middle Archaic in age, about 700-800 calendar years older than Zone 7.
I only wrote briefly about Unit 11, which I and several volunteers put in after field school to get our first good look at what is beneath the deposits exposed by the original machine cut. There wasn't much material until we neared the boundary of a seasonal water table. Right above that, there were some large cobbles and a very light scattering of small, angular quartz fragments. As I wrote back in May, none of the cobbles appears to have been modified (at least based on a macro inspection), and none of the pieces of angular quartz is a slam dunk for a human-made stone tool. Other than human deposition, however, I can't think of a good explanation for how that material got there -- it is so unlike its sandy matrix in terms of size that it could not have been transported by the same mechanism.
There are two main possibilities for the date: (1) it accurately dates the age of Zone 19; or (2) it doesn't.
It's possible that that piece of charcoal worked it's way down through the sand from a higher elevation, perhaps through bioturbation (movement by animals or roots). There's no obvious signs of intrusion from where the sample was taken, but that doesn't mean much in these old sands: we wouldn't necessarily expect that subtle signs of intrusion would be discernible in these kinds of sediments after 6000 years.
So the date could be "bad" in the sense that it isn't giving us the age of the deposit. I think it's entirely possible, however, that it is accurate. While the idea of a slow and steady accumulation of sand over the course of the Archaic is appealing, there's no reason to assume that that's how it went down. It's possible that rates of deposition varied. The levee could have aggraded more rapidly during the Middle Holocene, perhaps as a function of both Middle Holocene climate and the lower elevation of the existing surface at that time (making it easier for the landform to be over-topped by flood waters).
If Zone 19 really dates to around 4700 BC, the deposits in Zone 15 could be related to a deeply-buried Morrow Mountain occupation.
Investigating the deep deposits at 38FA608 is a top priority for excavations in the spring. Stay tuned!