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Steve Sheriff Professor of Geophysics, University of Montana

Imaging Furniture, Graves, and Stone Rings at Depth: Recent Magnetic and Radar Results from the Northern Rockies. Steve Sheriff Professor of Geophysics, University of Montana. Collaborators include: Doug MacDonald , Department of Anthropology, University of Montana

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Steve Sheriff Professor of Geophysics, University of Montana

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  1. Imaging Furniture, Graves, and Stone Rings at Depth: Recent Magnetic and Radar Results from the Northern Rockies Steve SheriffProfessor of Geophysics, University of Montana Collaborators include: Doug MacDonald, Department of Anthropology, University of Montana Elaine Hale, Yellowstone National Park Robert & Virginia O’Boyle, Integrity Resources Archaeology, Potomac, MT Garry Carlson, Gradient Geophysics, Missoula, MT

  2. Total Field Magnetics Subtle changes in subsurface magnetic properties create subtle changes in Earth’s magnetic field • measure Earth’s magnetic field at 1:500,000 • process data • interpret the maps • best cost-benefit tool • follow up with radar

  3. Yellowstone Lake – Total Magnetic Intensity ¼ hectarebroad signature is geologic; best to remove it Interesting zone Buried cable?

  4. Map Algebra: TMI – Regional = Residual Total Magnetic Intensity (TMI) Regional (relatively deep sources) Residual (for analysis) • NE corner looks even more interesting • clip out the northeast corner for further analysis

  5. Northeast Corner with regional removed • Strong, classic dipolar, central anomaly • Radial distribution of surrounding highs • Each anomaly has a source: geological, archaeological, or historic

  6. 3D model and excavation results • Central anomaly = furniture rock, base ~ 1 meter • Radial distribution of surrounding anomalies & sources suggest long term camping around that piece of furniture

  7. Ground Penetrating Radar – echoes off reflectors Transmit & receive radar waves (200–1000 MHz) Waves reflect off subsurface layers & objectsMake profiles and maps of the reflectors

  8. In search of a Historic Grave - Yellowstone Ground Penetrating Radar

  9. In search of a Historic Grave - Yellowstone GPR – across current pavement • 61 transects • 0.5 meter line spacing • 250 MHz antenna • .05 meter trace spacing

  10. In search of a Historic Grave - Yellowstone Ground Penetrating Radar • 5 transects and one time slice • Dashed line shows disrupted reflectors marking trench • Next: interpolate horizontal slices

  11. In search of a Historic Grave – Time Slices (map view) • Horizontal slice of radar volume at 0.6 meters depth • Lower edge of image follows current road edge • Magenta lines mark probable edge of an older road flanked by trenches

  12. In search of a Historic Grave– map view of radar • 1.5 meters deep • white box shows the most likely location of the historic grave

  13. Stone Rings: Kevin Rim, MT & Kelly Forks, ID Processed magnetic data Robert O’Boyle photo and data

  14. How deep could we bury the stone ring and still detect it? • Current anomaly • Mapped stones – a real mix of magnetizations • Recalculate to 1 meter deep – easily detectable ‘BURIED’ 1 m

  15. Buried stone rings at depth - Clearwater River, Idaho Easternmost grid

  16. Buried stone rings at depth - Clearwater River, Idaho • High energy fluvial deposits • 1930’s CCC camp • Recent construction

  17. Buried stone rings at depth - Clearwater River, Idaho • nice camp area • at least 2 stages of road construction • central anomalies are probable 1930’s CCC camp Left 1/3 is impacted by recent construction

  18. Zooming in: expect archaeological anomalies of 1’s – 10’s of nT Extremely high amplitude anomalies from bits of metal, tent stakes, survey pins, etc. Pre-filtering, nothing is very apparent

  19. Processed TMI: we expect anomalies of 1’s – 10’s of nanoteslas Circular features

  20. Compare a radar time slice • ~ 1 meter deep • Roughly the same area • GPR confirms the character of the magnetic anomalies

  21. GPR Time Slices Probable stone circles at about 1 meter deep Probable 1930’s road to CCC camp

  22. Combined Magnetics and GPRYellowstone National Park

  23. Raw and Residual Magnetics Raw data Regional removed

  24. Overlapping Ground Penetrating Radar Despite rough ground conditions (fallen logs, bunchgrass, and sagebrush) we acquired GPR data over part of the magnetic grid. GPR data collected over 10 meters of the magnetic grid. 500 MHz antenna 0.5 meter profile spacing trace separation of 0.05 meters

  25. 3D: GPR Features from Fluvial Structures Fluvial silts and sands below 0.90 meters, confirmed by auguring Time slice at ~1 meter Arcuate features result from horizontal sections through the fluvial structures.

  26. Results from Test Units • #1 - hearth (1,720 +/-40 B.P.) & evidence of obsidian tool manufacturing • #2, 3, and 4 yielded only boulders. Each individual anomaly has the character of a boulder yet their concentration and alignment was promising • #5 - hearth at about 0.8 meters (2,920 +/- 40 B.P.) • #6 - likely hearth dated at 3,090 +/- 40 B.P.)

  27. Noninvasive methods, substantial results Total Field Magnetics Ground Penetrating Radar

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