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Millions of years before present (MY)
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Era
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Period
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Epoch
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Formation
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Description
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| 0 (present) | Cenozoic | Quaternary | Holocene | Mickey Hot Springs active | |
| 0 | Cenozoic | Quaternary | Pleistocene | Diamond Craters | Alluvial, talus, landslide, playa deposits.Basaltic volcanic eruptions from ~25 KY |
| 1.8 | Cenozoic | Tertiary | Pliocene | Harney Formation | ~2.5 - 5.5 MY include tuffaceous sediments, olivine basalts, and Wrights Point Member |
| 5.5 | Cenozoic | Tertiary | Miocene | Danforth Formation | Includes several individual formations including the Rattlesnake Ash-flow Tuff (~7 MY), Tuffaceous sediments, Prater Creek Ash-flow Tuff (~8.2-8.6 MY)2, Devine Canyon Ash-flow Tuff (~8.75-10.3 MY) , and volcaniclastic rocks |
| 22.5 | Cenozoic | Tertiary | Miocene | Steens Basalt | ~16.6 MY Various flows during activity found in Steens Mountains and as basement unit in various outcrops and type sections throughout region. Steens Fault active, form Steens Mountains (horst) and Alvord Desert (graben) |
| 36 | Cenozoic | Tertiary | Oligocene | John Day Formation | Formed ~20 - 39 MY |
| 36 | Cenozoic | Tertiary | Eocene | Life in John Day Fossil beds dates back to late Eocene | |
| 59 | Cenozoic | Tertiary | Paleocene | Clarno Formation | Formed ~37 - 54 MY |
| 63 | Mesozoic | Cretaceous | Goose Rock Formation | Formed ~100 MY, consisting of ocean bottom deposits | |
| 135 | Mesozoic | Jurassic | |||
| 180 | Mesozoic | Triassic | |||
| 230 | Paleozoic | Permian | |||
| 280 | Paleozoic | Pennsylvanian/ Mississippian | |||
| 345 | Paleozoic | Devonian | |||
| 400 | Paleozoic | Silurian | |||
| 440 | Paleozoic | Ordovician | |||
| 500 | Paleozoic | Cambrian | |||
| 550 | Paleozoic | Cambrian | |||
| 600 | Precambrian | ||||
| 3400 | Archaean | Appearance of fossil bacteria in rocks-suggested first form of life. |
Sherrod, D. R., and Johnson, J., 1984. Geologic map of the Irish Lake Quadrangle, Harney County, South-Central Oregon. U. S. Geological Survey Miscellaneous Field Studies Map MF-2256.
Walker, G. W., 1979. Revisions to the Cenozoic Stratigraphy of Harney Basin, Southeastern Oregon. Geological Survey Bulletin 1475.
Bureau of Land Management, 1996. Oregon, Diamond Loop National Back Country Byway. U. S. Government Printing Office.
National Parks Service. Date unkown. http://www.nps.gov/joda/formations.htm.
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