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 16

ephemeral features that show a high degree of sinuosity and are responsible for
producing much of the modern dissected landscape. They drain into the Rio Bo-
quillas, west of the site and are over 2 km long. The channel widths average
approximately 2 m. The small channels are slightly sandy, but primarily are
composed of reworked silt. Barforms along the insides of channel meanders are
dominantly sandy, but may also be reworked sandy silt.
Dissected/Reworked Silt: Qdrs
These areas are underlain by silt that has been dissected by modern drainages and
reworked by fluvial processes. Many of the areas in Los Entierros and Los
Monticulos have been extensively dissected. Dissected silt surfaces often contain
more rock and fire cracked rock than the undissected silt. The localities where
fluvial reworking is established include Los Monticulos, the northern parts of Los
Entierros and western El Canal, and the areas immediately adjacent to the channels
that flow through the dissected areas. Often these reworked deposits are difficult to
distinguish from undissected silt. Some general characteristics for distinguishing
reworked silt are (1) the reworked silt shows evidence of small ripples and
other sedimentary structures, whereas non-reworked silt is homogenous, and
(2) the reworked silt has a slightly higher sand content. Reworked silt is often
present at the site as a ''cap'' that overlies the homogenous, undissected silt. In
areas of extensive erosion where the silt and upper parts of the paleosol have been
removed, reworked silt may directly overlie the paleosol.
Modern Disturbances: Qmd
Modern disturbances reflect historic modification of the landscape, with much of it
during the twentieth century. This unit is represented by constructed features such
as roads and canals.
Discussion
The landscape at La Playa is interpreted to reflect development during extremes
related to climatic shifts from the Pleistocene into the Holocene. The diverse grain
sizes present within its soils and sediments and the variety of compositions show
that different styles of sediment transport and deposition were active. Within the
paleosol, Pleistocene gravels that are present indicate significant transport by
rivers draining an extremely large catchment. The size of this drainage basin is