An Unexplored Realm in the Heartland of the Southern Gulf ... - Famsi

The features of the San Juan are characteristic of a meandering river system: a
sinuous channel, a wide floodplain containing abandoned channel segments, point bars or
areas of deposition on the convex or interior bank, and eroded banks on the opposing
concave side. At El Marquesillo, the site is on the outside edge of the meander, it is on
this outside arc of the curve where the water moves fastest. The speed of the water along
this bank erodes the channel wall, creating a cut bank. Figure 3.2 illustrates the site of El
Marquesillo atop this cut bank.
Figure 3.3 illustrates these features of a meandering river floodplain. This aerial
image of the topography at El Marquesillo show the scars left by the meandering
movement of the river course. Observation of the ancient channels suggests the
maximum distance the river migrated from its present course was less than a kilometer; a
distance that should not have caused any significant difficulties for occupants of El
Marquesillo. This suggestion is supported by the fact that Formative period occupational
areas and Late Classic architectural complexes are basically side by side; a situation that
would not be expected to occur if the river course had changed significantly.
Sequent aerial photographs of the same area show the changes in the river channel
and its effects on the archaeological site of El Marquesillo. Examination of aerial and
satellite imagery of the river at this location indicates that since the early 1970s the river
channel has remained constant and followed the 1991 course shown in Figure 3.3.
Accounts by long-term residents of El Marquesillo suggest this flow of the San Juan
River has remained unchanged since the late 1940s. The flow of the river is south to
north or bottom to top in the photos.
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