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Opal Butte, Morrow Co., Oregon, USA

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Latitude & Longitude (WGS84): 45° 2' 38'' North , 119° 36' 44'' West
Latitude & Longitude (decimal): 45.04389,-119.61222
Köppen climate type:Csb : Warm-summer Mediterranean climate

Extra Lapis - English No. 10 Opal

Mineral List

2 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

Early Miocene - Late Eocene
15.97 - 37.8 Ma

ID: 2786504
John Day Formation of east-central Oregon

Age: Cenozoic (15.97 - 37.8 Ma)

Stratigraphic Name: John Day Formation

Description: John Day Formation of east-central Oregon (lower Miocene, Oligocene, and uppermost Eocene?)

Comments: Unit in La Grande 30' x 60' quadrangle (OR291), reinterpreted as part of Oligocene and early Miocene Tower Mountain volcanic field with the main vent a 14-km-wide caldera (Tower Mountain caldera). Vent-filling ash-flow tuff is intruded by dacite and rhyolite plugs and dikes and ringed by a belt of rhyolite domes and flows. The caldera margin is coincident with prominent gravity and aeromagnetic anomalies. The volcanic field contains 18 map units that range in composition from basalt to rhyolite. Unit in Umatilla River Basin (OR292) is reinterpreted as Herren Formation, consisting mainly of interbedded arkosic sandstone, mudstone, and carbonaceous shale. Also contains micacaous sandstone and siltstone. Section on East Birch Creek is interpreted as a deltaic sequence that coarsens upward. Leaf fossils are abundant locally and collections from Birch and Pearson Creeks indicate a late Paleocene to early Eocene age.

Lithology: Major:{sandstone mudstone}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Oligocene - Eocene
23.03 - 56 Ma

ID: 1475762
John Day/Clarno Group

Age: Paleogene (23.03 - 56 Ma)

Stratigraphic Name: John Day Formation

Description: Tuffs, tuffaceous sedimentary rocks, and minor interbedded flows; sedimentary/volcanic rocks; mixed lithologies; mixed lithologies; crystals/grains

Lithology: Major:: {tuff, white, grayish yellow, very pale orange, pinkish gray}; Major:: {ash-flow tuff, very pale orange, pinkish gray, white, grayish yellow}; Major:: {tuffaceous sediment, grayish yellow, white, very pale orange, pinkish gray}; Major:: {lapilli tuff, very pale orange, pinkish gray, grayish yellow, white} Minor:: {rhyolite flows}; Minor:: {andesite flows}; Minor:: {rhyodacite flows}

Reference: R.L. Smith, W.P. Roe (compilers). Oregon Geologic Data Compilation, release 6. State of Oregon Department of Geology and Mineral Industries. [20]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

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