Like a window cut through lava flows and underlying strata, so have water and time worked to strip away the upper John Day Basin's basalt cap. What at erosion has exposed there is representative of a much larger region, one where tremendous outpourings of lava in the distant past covered much of what is now the Pacific Northwest. An unusually coherent geological record spanning some 40 million years can thus be seen rather easily, though its size and complexity still has much to offer science after more than a century of study.
The upper John Day Basin provides evidence of evolutionary changes taking place during the Cenozoic Era, some 65 million years ago to the present. This era is divided into two periods, the Tertiary and Quaternary, which are further separated into epochs. The Tertiary Period consisted of five epochs: Paleocene (65 million years ago to 55 mya), Eocene (55 mya to 38 mya), Oligocene (38 mya to 25 mya), Miocene (25 mya to 5 mya), and Pliocene (5 mya to 2 mya). These preceded the Pleistocene (2 mya to 10,000 years ago) and Holocene (10,000 years ago to present) epochs of the Quaternary Period.
To tie the geologic time scale with local layers of rock (called beds), similar strata are grouped into a more conspicuous unit known as a formation. Comparisons with strata elsewhere allow for correlation of these formations with a place on the geologic time scale. A sequence of formations can be correlated with Tertiary epochs in the upper John Day Basin, thereby allowing for study of evolutionary change over a long period with fossilized evidence. Furthest back in time of these formations is the Clarno (Eocene), followed by the colorful John Day (Oligocene), Picture Gorge Basalt (Upper Miocene), Mascall (Middle Miocene), and the Rattlesnake (Pliocene). Except for the Picture Gorge Basalt (which is part of the Columbia River Basalt that covers a much larger area), each of these formations contains fossils. All of them are clearly represented within the monument's boundaries, a highly unusual occurrence for a relatively small area.
Magnificent combinations of quality and diversity in the fossils, coupled with the length of time represented are the characteristics that make the John Day Basin internationally significant.  Vertebrate faunas in the Clarno, Painted Hills, and Sheep Rock units lie in close proximity to associated volcanic ash layers, magnetically altered rocks, polynomorphs, and floras. These associations span 40 million years of environmental change and allow comparison of the John Day fossil populations with those recovered from sediments of similar age throughout the world. The collective aim among paleontologists in doing this is, of course, to find global patterns of terrestrial floral adaptation and evolution of faunas. 
Popular recognition of the John Day Basin's importance to paleontology has been evident throughout the 20th century. Writing in 1901, John C. Merriam described its significance to readers of one national magazine:
"Although there are other geological sections, particularly in the Western United States, which furnish as remarkable [a] history...there are probably none in which the relations of the various chapters [of geological time] to each other are more evident than they are in the record inscribed on the walls of the John Day canyon. The deciphering of the geologic story of most regions is accomplished through the enthusiastic labors, over wide areas, of men taught to see things which escape the notice of untrained observers. The John Day section tells its story so plainly that to one who sees the record a comprehension of its meaning is unavoidable. " 
Over sixty years later, paleontologist J. Arnold Shotwell summarized the basin's importance in a report to the National Park Service (NPS) which supported establishment of a national monument:
" There is no question of the national or international significance of the John Day Basin. It has been clear for one hundred years. Neither is there any question of the clarity of the story to be seen by the visitor, [as] this is its chief value... Other areas now part of the National Park Service; Dinosaur, Agate Springs, Badlands and Flourisant, all deal with single chapters or some unique aspect of single chapters in the history of life. The John Day Basin offers an entire book!" 
The monument's significance to paleontology as a field of study has also been enhanced by the opportunity to interpret ongoing excavation and preparation of fossils by park staff. These demonstrations are in keeping with the reasons behind transfer of three state parks which formed the basis for this national monument. State park officials recognized the upper John Day Basin's paleontological significance, but did not possess sufficient means to convey its importance and foster public appreciation of why fossil resources warrant protection.
Last Updated: 30-Apr-2002