Curry Draw, Cochise County, Arizona, United States
Murray Springs
About 12,900 years ago (Clovis camp under a black mat)
A hunting camp, with mammoth and bison on the gravel, is sealed by a thin black clay. The clay is a wetland, and it has also been treated as the calling card of a comet. The camp is secure. The calling card was checked here, and it did not hold in the form that was claimed.
Why this is extraordinary
In Curry Draw, in the San Pedro Valley of southeastern Arizona, Clovis hunters left a camp on a stream gravel. Hundreds of stone tools lay there with the bones of two mammoths and eleven bison, and with horse and dire wolf as well. On that surface sits a black mat, a dark organic clay a few centimetres thick, read as an algal bloom or as a wetland soil. Charcoal, probably from hearths, eight dates averaged, gave 10,900 radiocarbon years, plus or minus 50, which is about 12,900 calendar years. The mat itself dates from about 10,700 radiocarbon years at its base to about 9,700 at its top. It kept forming through the cold centuries of the Younger Dryas, not in an afternoon.
The mat became famous a second time when researchers used it as a sample for a proposed cosmic impact at that same moment, offered as the cause of the cold, of the end of Clovis, and of the extinctions. A later sampling of the layer, by people who know the stratigraphy, did not find an iridium spike or a radiation anomaly. Magnetic microspheres were there. Microspheres have both earthly origins and ordinary cosmic-dust origins, and the continent-scale burning that had been claimed was not in the evidence this group reviewed. They were plain about the limit of that result. It does not forbid a cosmic event. It does forbid treating Murray Springs as a place where those particular signatures were confirmed.
Other dark wetland layers, older and younger than 12,900 years, carry similar chemical markers, including ground under this mat that is already older than the boundary. A marker that shows up in many marshes is a weak passport for one impact. The camp, the animals, and the dark layer are the site. The impact is a hypothesis that borrowed them, and it is weighed on its own in the Younger Dryas room.
Why it matters
Murray Springs is one of the clear places where Clovis tools, extinct animals, and the start of the Younger Dryas cold can be seen in one bank. If the black mat is only a marsh that spread when the climate flipped, the extinction and the culture change still need a cause, and the marsh is a consequence, or a neighbour. If the mat is impact debris, this draw is a ground zero. The resampling is why this room does not call it that.
Clovis, here, is the tool tradition of fluted spear points, spread across the continent and brief, centred near 13,000 years ago. The Younger Dryas is the cold return from about 12,900 to 11,700 years ago. A black mat in this valley is organic clay, stratum F2 in the local lettering, generally 2 to 10 centimetres thick. Radiocarbon years are not calendar years. The figure 10,900 is radiocarbon, and the figure 12,900 is the calibrated reading given with those dates.
Photo tour
2 photographs, unedited. On a phone, swipe the row. Choose one to look closely.
- No openly licensed photograph in this room isolates the black mat as a labeled band. The trail pictures show the draw and the bank, not the contact that was excavated.
What is still unexplained
These sit beside the consensus account, with the same visual weight. None of them is marked solved.
Location and dating
- Location
- Murray Springs lies in Curry Draw, east of Moson Road and north of Arizona Highway 90, west of Sierra Vista, in Cochise County. The pin is about 31.57° N, 110.18° W.
- Period label
- Current consensus — open to revision The Clovis occupation falls about 12,900 calendar years ago. The black mat goes on forming through the Younger Dryas, into ages near 9,700 radiocarbon years at its top. The animals on the gravel are the terminal Pleistocene fauna.
- How this dating was done
- Radiocarbon on ash-wood charcoal from the occupation, and on organic matter in the black mat, is read in the stratigraphy of channel gravel, mat, and marl. The impact markers are chemistry and microscopy, which does not date the layer, because the date is the carbon.
- What could change it
- What would settle more of this is a section, still open, in which the mat, the Clovis surface, and any exotic markers are sampled by a crew that did not propose the impact, at a spacing tight enough to show whether a spike is a layer or a smear.
What is actually there
- Tools and the bones of two mammoths and eleven bison lay together on one surface under the mat.
- Horse and dire wolf were in the bone as well.
- The mat is organic clay, about 2 to 10 centimetres, and it is thicker off the old channel.
- A resampling did not find an iridium anomaly or a radiation anomaly in the layer.
- Similar markers turn up in wetland mats of other ages, including in the silt under this mat.
Open questions
| Question | Status |
|---|---|
| Did the cold make the marsh, or did one event make the cold, the marsh, and the extinctions together? | The marsh matches a wetland response to climate. The single-event reading is the impact hypothesis, and it is not confirmed in this bank. |
| Why do the Clovis tools stop at this surface? | Open. The mat buries the camp. Burial is not the cause of a culture’s end across a continent. |
The current narrative
Where publication stands today. It is the best-supported reading, and it is open to revision. It is not a verdict.
The current narrative — open to revision
A Clovis camp buried by a Younger Dryas marsh
People hunted mammoth and bison here about 12,900 years ago. A wetland soil then spread over that surface and kept forming through the cold period. The extinction and the end of Clovis line up with the cold. The mat records the wet ground, and it has not yielded the impact signatures that were claimed from it.
What supports this
- Tools in place with the animals, under a sharp contact.
- Eight charcoal dates sit at 10,900 plus or minus 50 radiocarbon years.
- The mat's thickness, and its stringers, follow the old low ground.
- A resampling did not recover the iridium anomaly, or the radiation anomaly.
What pushes back
- The excavators of the layer have also written that the extinction looks sudden, and that an impact, though not compelling, deserved more tests.
- The coincidence of the camp, the bones, and the climate flip is exactly the pattern the impact reading was built to explain.
- Absence of iridium here is not the same as absence everywhere.
What would settle it
The camp and the wetland hold. The impact does not hold as a result from this site. The wider claim lives in the other room, where the same standard is applied to the other markers.
Emerging narratives
Other published readings. Each may be right. None is adopted here unless the evidence carries it.
An emerging narrative
The black mat is the impact boundary
The dark layer is the debris and the burn of a cosmic event that ended the megafauna and Clovis together, and Murray Springs is a type locality for that boundary.
What supports this
- The mat sits on the last Clovis surface, and on the last bones of several extinct species.
- Its age matches the start of the Younger Dryas cold.
- Microspheres are present, and some cosmic-dust spheres fall all the time, so a sphere is a fair thing to look for.
What pushes back
- Iridium, and a radiation anomaly, were looked for and not found.
- The mat grew for centuries, which is a marsh's pace, not a fallout's.
- The same class of marker shows up in mats of other ages, and in older silt at this very site.
What would settle it
It is a reason this site was sampled, not a result the resampling upheld. It stays on the table only as part of the continental argument, not as a finding in this draw.
Should the current view be reevaluated?
Consensus holds well
Murray Springs is a Clovis camp under a wetland clay of Younger Dryas age, and that part holds. Using the clay as proof of an impact does not hold on the resampling published from the same layer. Markers sitting in marshes of many ages are a further reason not to read one dark band as a unique catastrophe.
What drives this
- Tools and megafauna together on one buried surface.
- Charcoal at about 12,900 calendar years.
- A mat that thickens the way a wetland does, and that dates through the cold period.
- A failed confirmation of the iridium and radiation claims at this site.
This is the museum’s own weighing of the evidence. It is not a visitor vote, and it is separate from the slider.
Weigh it yourself
Anonymous. Nothing here is stored except on this browser. Your lean does not change the assessment beside it.
Visitor lean so far — not evidence. On this browser only; a shared tally is not collected.
If the contested reading is right
What would follow if a reading that is not the consensus turned out to be true, and what could settle it. This explains the stakes. It does not adopt the reading.
An impact happened, and this site simply did not preserve the markers
Murray Springs would drop out of the impact map, and the hypothesis would have to depend on other places. The camp would still be a Clovis hunt at the start of the cold. Preservation would then have to explain why a type locality missed the signal it was cited for.
Why it is still worth a test
The same tests, published in full, at the sites where the markers were reported, run by crews who did not collect the original samples.
Hunting, not climate and not a comet, ended the animals here
The mat would be only a lid on a camp that had already done the killing. Eleven bison and two mammoths are a hunt, and they are not, by themselves, a continental extinction. The other valleys would have to match.
Why it is still worth a test
A count of kills set against a count of animals, across the San Pedro sites, in dated order.
Sources
- The Murray Springs Clovis site, Pleistocene extinction, and the question of extraterrestrial impact Proceedings of the National Academy of Sciences
- Younger Dryas black mats and the Rancholabrean termination in North America Proceedings of the National Academy of Sciences
- Accumulation of impact markers in desert wetlands Proceedings of the National Academy of Sciences
Image credits
- The interpretive trail at the Murray Springs Clovis site, west of Sierra Vista. The occupation sits in the sediments rather than in the brush, and no open photograph here shows the black mat as a labeled layer.. Ammodramus, CC0. Shown unedited.
- The incised wash at the site, with the trail beyond it. The bank is the kind of cut in which the layers were read, and this frame does not identify the black mat.. Ammodramus, CC0. Shown unedited.