Overview
In a shallow rockshelter tucked into the Oregon high desert, archaeologists encountered a contradiction that does not resolve easily.
At Rimrock Draw Rockshelter (site 35HA3855), excavations uncovered an orange agate stone tool and fragments of extinct camel tooth enamel buried beneath a continuous layer of volcanic ash. That ash—chemically matched to a Mount St. Helens eruption—is securely dated to about 13,000 BC.
The material below it, however, tells a different story. Dating of the associated camel remains places human activity at the site around 16,300 BC, several thousand years earlier than expected under traditional migration models.
The Geological Seal
The defining feature of Rimrock Draw is not the artifact itself, but where it was found.
Excavators identified a laterally continuous, unbroken layer of volcanic tephra across the site. Geochemical analysis linked this ash to a known Mount St. Helens eruption, providing a firm chronological marker. In stratigraphic terms, the ash functions as a sealed lid—a boundary that should prevent later materials from intruding into older deposits without visible disturbance.
The orange agate scraper was recovered below this ash layer, embedded in compacted sediments that showed no signs of mixing or collapse. If the stratigraphy is intact—and multiple profiles indicate that it is—the artifact must predate the eruption that deposited the ash.
The Artifact: Item 467
The object recovered from beneath the ash is a small scraper fashioned from orange agate.
On its own, such a tool could be dismissed as a naturally fractured stone. To test this, researchers conducted residue analysis on the working edge. Protein testing identified residues consistent with bison blood, indicating the tool was used to process animal tissue.
This shifts the object from a geological curiosity to a behavioral artifact. Someone used it, and that use occurred before the ash sealed the deposit.
Camelops and Context
The scraper was not found in isolation.
In the same stratigraphic component, excavators recovered fragments of tooth enamel belonging to Camelops, an extinct genus of Ice Age camel. Scientific dating of this enamel places it at approximately 16,300 BC.
Camelops disappeared from North America near the end of the last Ice Age. Its presence at Rimrock Draw anchors the deposit firmly in the late Pleistocene and provides an independent line of evidence consistent with the tool’s stratigraphic position.
Implications for Early Migration
For much of the twentieth century, the Clovis First model suggested humans arrived in North America around 11,000 BC, coinciding with the opening of an ice-free corridor between the continental ice sheets.
Rimrock Draw complicates that picture.
An occupation dating to roughly 16,300 BC would place people in the interior Pacific Northwest several thousand years earlier, at a time when that inland corridor was likely still blocked. This does not prove a single migration route, but it is consistent with scenarios involving earlier movement along the Pacific coast, followed by later travel inland.
What Rimrock Draw does not tell us is who these people were, how long they stayed, or whether their presence represents a brief visit or a sustained occupation. The site preserves activity—but not identity.
What Remains Unresolved
The evidence at Rimrock Draw is unusually well constrained in one respect and frustratingly silent in others.
The when is anchored by stratigraphy and absolute dating.
The what is supported by residue analysis and extinct fauna.
The who, however, remains invisible.
No burials, no genetic material, and no diagnostic projectile points have been recovered from the anomalous layer. The ash preserved the context—but it also sealed away much of the human story.
For now, Rimrock Draw stands as a reminder that the archaeological record is both precise and incomplete. The tool survived. The ash survived. The people did not.
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This case file is part of the North America Arc.
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