CA-MNT-1918

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Cultural Chronology

Radiocarbon Determinations - Obsidian Studies - Summary

Chronmetric data from CA-MNT-1918 were limited to two radiocarbon dates and two obsidian hydration readings. No beads were recovered. With such a small data set, projectile points become potentially more important as chronological indicators since they were recovered in abundance, and previous studies have demonstrated that some types are temporally meaningful.

Radiocarbon Determinations

As mentioned above, charcoal samples intended for radiocarbon analysis were obtained from bulk midden samples taken from exposed sidewalls. This procedure was used because no shell or bone samples, suitable for dating were found in the deposit due to soil acidity. No features with clearly cultural charcoal were identified. Bulk midden samples are potentially problematic because of the abundant evidence for rodent activity within this deposit (and virtually all other sites at FHL). An attempt was made to obtain the flotation samples from areas that showed no obvious signs of rodent activity, but this did not proclude the possibility, indeed the likelihood, of rodent activity at some other time in the past. Fires are a frequent occurrence within FHL today, and were equally common historically. These include intentional or prescribed burns, intentional burns that escaped control, and natural or lightening-caused blazes. Both intentional burns and natural fires also occurred in the region prehistorically. All such fires have the potential to produce charcoal which can, in turn, be worked into the soil by rodent activity. Soil charcoal, therefore, cannot be assumed to be of cultural origin, but may instead reflect natural or other fires that occurred in the area unrelated to the occupation and use of site CA-MNT-1918.

The two charcoal specimens were both obtained from the same flotation sample number 1 which was collected from the 30-50 cm level of unit 7, Stratum Ib. The first, a charred pine nut fragment, produced a calibrated calendric age of 2880 B.C. (one sigma range of 2880-2700 B.C.). As will be discussed in more detail below, this sample is thought to relate to the prehistoric occupation. The second specimen, a charred acorn from the same bulk sample, yielded a calibrated calendric age of A.D.1330-1400 (one sigma range of A.D. 1320-1410). The occurrence of charcoal specimens with such disparate dates in the same provenience is a clear reflection of the bioturbated soils that are common within FHL. In this instance, the later date is thought to be unrelated to the prehistoric site occupation.

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Obsidian Hydration and XRF Results

Only two pieces of obsidian were available for analysis. Specimen 1918-3-16 from the 20-30 cm level of Unit 3 was from the Napa Valley source and produced a hydration rim of 5.5 microns. Specimen 1918-7-066, from the Annadel source, produced a reading of 1.9 microns. The Napa reading is consistent with the earlier radiocarbon date of 2880 B.C., while the reading on Annadel could be taken as support for the more recent C14 result of A.D. 1400, but this is considered unlikely two several reasons. First, when hydration results diverge from radiocarbon results on the central coast they commonly are much younger (i.e., they yield thin hydration bands) than the C14 results (see Jones and Ferneau 2002). In other words, hydration results suggesting more recent site occupation seem to be common and most commonly inaccurate. Second, as detailed below, nothing in the artifact assemblage recovered from the midden suggested occupation during the Late Period.

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Summary

The chronometric findings are not ideal in that the recovery of samples with dates over 4,000 years apart from the same bulk sample demonstrates the problems with non-feature derived dating samples. On face value alone, the radiocarbon and hydration results can not be reconciled in terms of their conflicting chronological implications. The artifact assemblage recovered from the same general provenience, however, is typologically cohesive and consistent with the Early Period radiocarbon date. The span of the Early Period occupation cannot be accurately determined from the available data so the site is tentatively ascribed to the whole of the Early Period: 3500-1000 B.C.

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References Cited

Jones, T.L., and J. Ferneau
2002 Deintensification Along the Central California Coast. In Cultural Complexity Along the California Coast: The Late Holocene, edited by Jon Erlandson and Terry Jones, University of California, Los Angeles Institute of Archaeology.