John Day Fossil Beds National Monument
Shows an overview map of the National Monument with other points of interest.
Like Icing on a Cake. "Between 16.6 million and 15 million years ago, eastern Oregon sat above the nascent Yellowstone hot spot's rising jet of basalt... basalts literally flooded from these 10-to 25-mile-long cracks, at first ponding in low places, then gradually filling and leveling the landscape, much like cake icing fills the imperfections in the surface." (From In Search of Ancient Oregon by Ellen Bishop). The Columbia River Basalt Group eruptions occurred in phases and from several locations. Hundreds of basalt floods issued from scores of fissures in the Earth's crust, covering over 62,000 square miles of the northwest. Some of the floods were so fluid and of such volume that they reached the ocean. A. This is your location on the southern edge of the basalt flows. The layers of basalt flows before you, in Picture Gorge and on the ridge to the north, are about 1,000 feet in thickness. The layers in the gorge are now tilted but were horizontal when formed. Beneath Yakima, Washington, the basalt layers are bout 15,000 feet thick. B- It is likely that a large rising plume of magma, from a stationary hot spot deep in the Earth, pushed up through cracks in the crust in several places, flooding out onto the surface
An Expanding Plain. You are standing on ashy deposits called the Mascall Formation, part of a story fifteen to twelve million years old. As the climate brought cooler, drier air, the remains of expansive hardwood forests continued to give way to plains of fertile grassland- and evolving savanna. This savanna was drummed with the hooves of camels, horses and antelope. Falcons pierced the sky. Originating from a distant continent, early elephants lumbered upon this landscape for the first time. Carnivores- huge bear-dogs, cat-like sabertooths, and dogs- hunted the growing herds of grass-eaters and dwindling numbers of forest dwellers. As this drama of life played out, periodic volcanic ash falls from the west and east dusted and layered the land. Entombed were the remains of plants and animals, preserved for the future as fossils. Though they lived in the distant past, Mascall Formation fossils seem very familiar when compared to life today. They are more familiar than the John Day country plants and animals tens-of-millions of years older, from earlier in the age of mammals.
A Volcanic Inferno. Imagine standing at the bottom of a long mountain
Erected by National Park Service.
Location. 44° 30.014′ N, 119° 37.321′ W. Marker is near Dayville, Oregon, in Grant County. Marker can be reached from County Road 40 (County Route 40). Touch for map. Road to the Mascall Overlook is well marked on Highway 26 about 4 1/2 miles west of Dayville, Oregon. Marker is in this post office area: Dayville OR 97825, United States of America.
Other nearby markers. At least 1 other marker is within 3 miles of this marker, measured as the crow flies. Picture Gorge Basalts (approx. 2.2 miles away).
Categories. • Environment • Paleontology •
Credits. This page was last revised on October 1, 2017. This page originally submitted on September 26, 2017, by Don Hann of Canyon City, Oregon. This page has been viewed 43 times since then. Photos: 1, 2, 3, 4, 5, 6. submitted on September 26, 2017, by Don Hann of Canyon City, Oregon. • Bill Pfingsten was the editor who published this page.