Near Dayville in Grant County, Oregon — The American West (Northwest)
Picture Gorge Basalts
John Day Fossil Beds National Monument
The bottom two layers of the gorge are the same two that cap Sheep Rock peak, behind you. In recent centuries, American Indian pictographs were drawn upon the rock, giving the gorge its name.
As the surface of each new lava flow rapidly cooled to a crust, the interior remained hot and somewhat fluid for many years. Heat released above the hot flow into the atmosphere was much faster than heat released from the bottom into the earth. A jumbled, shattered appearance in the hardened, upper layer resulted from the quicker cooling, and subsequent cracking of the lava flow downward from the top.
Over 70 miles to the south, a violent volcanic explosion sent a fiery torrent of superheated gases, ash, and large particles sweeping across the surface of the land. This surge slowed and settled, welding into hard rock called ignimbrite. The high, flat-topped mesa, capped with his ignimbrite layers, is part of the Rattlesnake Group.
Erected by National Park Service.
Location. 44° 31.873′ N, 119° 38.122′ W. Marker is near Dayville, Oregon, in Grant County. Marker is on Oregon Route 19 0.2 miles north of U.S. 26, on the left when traveling north. Click for map. Marker is just north of the southern entrance into the Sheep Rock Unit of John Day Fossil Beds National Monument. Marker is in this post office area: Dayville OR 97825, United States of America.
More about this marker. The background photograph of the marker shows the marker itself and its relative location in the gorge.
Categories. • Natural Features •
Credits. This page originally submitted on , by Duane Hall of Abilene, Texas. This page has been viewed 336 times since then and 20 times this year. Photos: 1, 2, 3, 4, 5. submitted on , by Duane Hall of Abilene, Texas. This page was last revised on June 16, 2016.
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