Quaternary Stratigraphy of the La Playa Archaeological Site (SON F:10:3), Northern Sonora, Mexico - Reconstructing Human-Landscape Interactions: Interpreting Desert and Fluvial Environments - page 7

Fig. 3 Cultural chronology for Arizona and northern Mexico from Watson ( 2010 ). Used with
permission of the author. Dates are calibrated radiocarbon years before present (BP)
Twelve thousand years of human history is documented by thousands of
roasting pits, hundreds of human burials, dozens of activity areas, dozens of canine
burials, a possible boarded field system, hundreds of projectile points, and thou-
sands of pieces of flaked stone, ground stone, shell, and pottery (Carpenter et al.
2005 ). Consistently, the lack of discernable stratigraphy and extensive modern
erosion that characterizes the silt at La Playa has made it difficult to understand the
relative chronology of features and samples, and in turn the geomorphic and
environmental contexts of the archaeological remains.
The most intensively investigated element of La Playa has been the human
burials. Currently, a sample of 327 mortuary features has been excavated.
Hundreds more are eroding out on the La Playa landscape, and hundreds more
likely remain intact beyond the current erosional edge. Most burials are believed to
date to the San Pedro (3,700-2,600 cal BP) and Cienega (2,600-1,900 cal BP)
phases of the Early Agricultural period, and a sample of 40 bone collagen
radiocarbon assays support this temporal assignment (Watson 2005 ).
Characterization of Soil and Sediments and Surficial Mapping
Since there is no detailed topographic model or mapping for the La Playa site,
much of the surficial mapping effort utilized a Quickbird satellite imagery base.
The Quickbird imagery consists of two imagery products. One is a four-band
product that includes a near-infrared band and has a spatial resolution of 2.4 m.
These bands cover the visible to near infrared range of wavelengths from 430 to
918 nm. The near infrared Quickbird imagery (bands 4-3-2) was particularly
useful for defining areas of firecracked rock (linear and circular features in black),
gravels and pavements (black to gray, smooth textured patches), the palesol
(yellow) and dissected units (white). The second product is a panchromatic single
band with a spatial resolution of 60 cm. The panchromatic image allowed
examination of the surface geomorphology and sediment types at La Playa at a
high spatial resolution which was used for accurately defining unit contacts. The
surficial mapping integrated the Quickbird imagery with field examination of
surface and cutbank exposures of the sediment types. GPS locations of specific