The uppermost section of the Red River Valley in the Caddo Homeland had major mound centers and smaller sites along it throughout most of Caddo history. Few of these sites are very well known. Major excavations were carried out at the Sanders site in Lamar County, Texas in 1931 by A.T. Jackson of the University of Texas. The graves he excavated contained pottery and other grave goods that are unlike anything else known in the Caddo Homeland. The Sanders focus was defined on the basis of these materials and remains an anomaly and the subject of considerable debate.
Although long considered a purely Caddo site, Sanders is thought by Frank Schambach to have been a trade goods collection center (entrepot) established or controlled by traders from Spiro. The chief trade good is suspected to be bois d'arc wood and/or bows made from this wood. The Sanders entrepot hypothesis has yet to be widely accepted. Nonetheless, there was a strong connection between this area of the Red River Valley and Spiro during Middle Caddo period, roughly A.D. 1200-1400. By historic times there were apparently no Caddo settlements in this stretch of the valley.