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Plum Bayou Mounds
Between 650 and 1050 CE, the Plum Bayou people built 18 earthen mounds on an oxbow lake in Arkansas. They positioned several mounds to align with sunrise and sunset on solstices and equinoxes, creating an earthen calendar for farming and ritual cycles.
The site served as the primary religious center where only a few leaders lived but many came for ceremonies. Then around 1050 CE, they vanished without a trace…