John Day Formation
Encyclopedia
The John Day Formation is series of rock strata exposed in the John Day River
basin of north-central Oregon
in the United States. The strata, which vary in age from 39 million years to 18 million years, were formed mainly from ashfalls from volcanoes to the west. Some of the major layers within the group are the Big Basin Formation and Bridge Creek Beds (35 to 32 million years), the Turtle Cove Formation (30 to 28 million years), the Picture Gorge Ignimbrite (28.7 million years), the Kimberly Formation (28 to 25 million years), and the Haystack Formation (25 to 18 million years).
Located in the general vicinity of what would become the Cascade Range
, the John Day volcanoes emitted large volumes of ash and dust, much of which settled in the John Day basin. The rapid deposition of the ash preserved the remains of plants and animals living in the region. Some of the solidified ash and the fossils they contain are found in the John Day Fossil Beds National Monument
. Because ash and other debris fell during varied climatic and volcanic conditions and accumulated from many eruptions extending into the early Miocene
(about 20 million years ago), the sediment layers in the fossil beds vary in their chemical composition and color. Laid down on top of older rocks known as the Clarno Formation, the John Day Formation consists of several distinct groups of layers. The lowermost contains red ash such as that exposed in the Painted Hills Unit of the national monument. The layer above it is mainly pea-green clay. On top of the pea-green layer are buff-colored layers. Fossils found in the John Day Formation include a wide variety of plants and more than 100 species of mammals, including dogs, cats, oreodont
s, horses, camels, and rodents. Among the notable plant fossils are the Metasequoia
(dawn redwood), a genus
thought to have gone extinct worldwide until it was discovered alive in China in the early 20th century.
John Day River
The John Day River is a tributary of the Columbia River, approximately long, in northeastern Oregon in the United States. Undammed along its entire length, the river is the third longest free-flowing river in the conterminous United States. There is extensive use of its waters for irrigation. Its...
basin of north-central Oregon
Oregon
Oregon is a state in the Pacific Northwest region of the United States. It is located on the Pacific coast, with Washington to the north, California to the south, Nevada on the southeast and Idaho to the east. The Columbia and Snake rivers delineate much of Oregon's northern and eastern...
in the United States. The strata, which vary in age from 39 million years to 18 million years, were formed mainly from ashfalls from volcanoes to the west. Some of the major layers within the group are the Big Basin Formation and Bridge Creek Beds (35 to 32 million years), the Turtle Cove Formation (30 to 28 million years), the Picture Gorge Ignimbrite (28.7 million years), the Kimberly Formation (28 to 25 million years), and the Haystack Formation (25 to 18 million years).
Located in the general vicinity of what would become the Cascade Range
Cascade Range
The Cascade Range is a major mountain range of western North America, extending from southern British Columbia through Washington and Oregon to Northern California. It includes both non-volcanic mountains, such as the North Cascades, and the notable volcanoes known as the High Cascades...
, the John Day volcanoes emitted large volumes of ash and dust, much of which settled in the John Day basin. The rapid deposition of the ash preserved the remains of plants and animals living in the region. Some of the solidified ash and the fossils they contain are found in the John Day Fossil Beds National Monument
John Day Fossil Beds National Monument
John Day Fossil Beds National Monument is a U.S. National Monument in Wheeler and Grant counties in east-central Oregon. Located within the John Day River basin and managed by the National Park Service, the park is known for its well-preserved layers of fossil plants and mammals that lived in the...
. Because ash and other debris fell during varied climatic and volcanic conditions and accumulated from many eruptions extending into the early Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
(about 20 million years ago), the sediment layers in the fossil beds vary in their chemical composition and color. Laid down on top of older rocks known as the Clarno Formation, the John Day Formation consists of several distinct groups of layers. The lowermost contains red ash such as that exposed in the Painted Hills Unit of the national monument. The layer above it is mainly pea-green clay. On top of the pea-green layer are buff-colored layers. Fossils found in the John Day Formation include a wide variety of plants and more than 100 species of mammals, including dogs, cats, oreodont
Oreodont
Oreodons, sometimes called prehistoric "ruminating hogs," were a family of cud-chewing plant-eater with a short face and tusk-like canine teeth...
s, horses, camels, and rodents. Among the notable plant fossils are the Metasequoia
Metasequoia
Metasequoia is a fast-growing, deciduous tree, and the sole living species, Metasequoia glyptostroboides, is one of three species of conifers known as redwoods. It is native to the Sichuan-Hubei region of China. Although the least tall of the redwoods, it grows to at least 200 feet in height...
(dawn redwood), a genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
thought to have gone extinct worldwide until it was discovered alive in China in the early 20th century.
Works cited
- Orr, Elizabeth L., and Orr, William N. (1999). Geology of Oregon, 5th ed. Dubuque, Iowa: Kendall/Hunt Publishing Company. ISBN 0-7872-6608-6.