JOHN DAY FOSSIL BEDS John Day Fossil Beds: A Study (Preliminary)

GEOLOGY

The upper basin of the John Day River Drainage extends from the gorge at Clarno, near Clarno State Park, through all of the upstream drainage. The river, called the Middle Fork, has two branches: the North Fork and the South Fork. Numerous tributary creeks feed the river along its course. Elevation varies from approximately 2,500 feet at Clarno to 9,000 feet in the Strawberry Mountains, The regional climate is now semi-arid, but in the geologic past it ranged all the way to subtropical at the beginning of the Cenozoic era. Prior to this time most of the State was covered by the oceans. There is very little evidence of the invasion of the seas in the basin area where the older deposits are buried under the more recent Cenozoic rock which has not yet eroded away.

During the Cenozoic era, formations containing fossils were laid down. It represents earth history of the last 70 million years and is divided into two periods, of which Quaternary is the most recent 2 or 3 million years. This period in turn is divided into two epochs: the Recent includes current time to 1 million years ago; and the Pleistocene, from 1 to 3 million years ago. The previous period is Tertiary, which goes back 70 million years and is divided into five epochs: Pliocene, Miocene, Oligocene, Eocene, and Paleocene (listed in order of the youngest first). All but the Paleocene are recorded in the Upper John Day Basin.

Of the formations seen in the John Day Basin the oldest is called the Clarno. This extensive formation has outcrops beyond the basin area and is calculated to be 37 million years old. The formation consists of basaltic and rhyolitic flows, breccia, tuff, volcanic conglomerate, and some thin lenses of water-laid volcanic ash. Fossil plants and animals from the Clarno indicate an age of late Eocene and early Oligocene.

The John Day Formation, above the Clarno, was deposited after the Clarno was deformed. It, too, extends considerably beyond the basin. The upper formation is buff, the middle is green, and the lower is red tuffaceous siltstone. Much of the formation originated as volcanic ash. Fossil plants in the lower section confirm the late Oligocene age and the mammal remains in the upper section indicate the early Miocene age.

Overlying the John Day is the Columbia River Basalt (from the Miocene epoch), much of which has been removed by erosion, This lava was from great long narrow splits in the ground that spread the flow over extensive land areas. Repeated flows over millions of years built up great thicknesses of basalt. Davis Dike, among others, illustrates the source of the tremendous quantity of lava which covered northeast Oregon to a depth of 2,500 feet in places. These are not like volcanic flows that commonly eject from a single vent in a built-up mountain with secondary flows from fissures in the mountain side.

The next younger formation is the Mascall, directly on top of the Columbia. Present exposures are mostly in the John Day Basin where an exposure of 2,100 feet is in evidence. The formation is water-laid light-colored tuffaceous volcanic ash. Fossil remains indicate the Miocene age, approximately 15 million years old.

The 6.5 million year old Rattlesnake Formation on top of the Mascall is from the Pliocene epoch, the youngest of the Tertiary Period. It consists of bedded-tuffs, gravels, and sandstone of lacustruce and fluviatile origin, contains many fossils, and was dated by the potassium-argon method.

Erosion during the more recent Pleistocene epoch formed many terraces, talus slopes, and alluvial deposits. These deposits are the source of gold which figured so prominently in the initial settlement of this area.

JOHN DAY BASIN GEOLOGY

Resources and Geological Formations Map. (click on image for an enlargement in a new window)

Fossils

John Day Basin is primarily significant as a record of the earth's history displayed through rocks and fossils which cover a considerable period of time.

Pre-Tertiary: Although the most complete record of life is in the Tertiary rocks, this is not the beginning of the local record. Pre-Tertiary rocks more than 100 million years old are also present in the John Day Basin. The record indicates the presence of a sea in the area at this early date; ammonites, shore shells, and bones of swimming and gliding reptiles are present. Because it is overlain by a tremendous volume of younger rocks, this very early record is poorly represented in the basin.

Clarno Formation: The Clarno flora and fauna are the oldest Tertiary life in the basin. The flora fossils found here are sub-tropical; the laurel and palm families are well represented, Important fauna remains uncovered included crocodiles, amphibious and small running rhinoceros, brontotheres, tapirs and tiny horses, and peccaries and oreodonts—the pig-like artiodactyls.

Tiny horse of the Clarno Formation—about the size of a large dog; note the crushed skull.

John Day Formation: The character of the vegetation and fauna recorded in fossils of this formation changed remarkably from that found in the Clarno. The flora look more familiar to most Americans because of their temperate character, although some of the plants have relatives living only in Asia. Oaks, elms, sycamore, chestnut, basswood, birch, horn-bean, and maples are representative of plants found in the United States today; Metasequoia and Katsura of Asia are, however, important parts of the flora. One hundred and twenty species of fossil mammals have been identified from this formation. They vary from small relatives of the opossum through sabertooth cats, rhinoceros, oreodonts, horses, peccaries and giant hogs to beavers, dogs, rabbits, and pocket mice. Tortoises, lizards, snakes, and land snails also are commonly presented in the collection.

Leaves of the John Day flora, including dawn redwood, alder, birch, and Katsura tree.

Mascall Formation: This formation reveals other life changes, especially in the recorded flora. Common plants are swamp cypress, black oak, hickory, sycamore, a small leaf maple, gingko, box elder, elm, and over sixty other less common species of plants. They represent several kinds of local habitats, reflecting hillsides, ponds, stream borders and plains. Much of the fauna was derived from earlier animal life of the John Day Formation. Three-toed horses, elk-like Dromomeryx with horns rather than antlers, bear, and mastodons appear for the first time.

Rattlesnake Formation: The flora and fauna of this formation provide the last view of Tertiary life in the John Day Basin. Dryer climate had reduced vegetation to trees and shrubs along the stream courses, and at the higher elevations grassland had become extensive. The large single toed horse and antelope had invaded the area from the south; rhinoceros, camels, peccaries, and mastodonts were common large mammals. The small sloths from South America appeared for the first time in the basin. The oreodonts so abundant in earlier fauna were no longer present and the elk-like Dromomeryx were also gone.

History of Research and Fossil Collecting

During 1861 Thomas Condon, a minister, moved to The Dalles, Oregon to establish a pioneer church. In traveling this vicinity he found fossils in some of the formations near The Dalles. Occasionally he would give brief lectures about the fossils and was recognized as a local authority on the subject. By 1864 people were bringing specimens from greater distances and Condon's collection increased in size. By 1871 Condon knew enough about the area that he published, in the Overland Monthly, an article describing the geologic history of the area. Condon later became a member of the staff of the University of Oregon.

In 1873 Le Conte, from the University of California, surveyed the basin and collected samples for study at the university.

The best known collector to visit the area and take samples for study was J. C. Merriam who made his first trip in 1899 while still at the University of California. He made numerous subsequent trips while still at California and later at Carnegie Institute. He also spent a short time at the University of Oregon where he continued his studies of the John Day area.

R. W. Chaney collected and studied in the area over a 40-year time span, starting with the Clarno Formation flora and later studying the John Day Formation.

J. A. Shotwell, University of Oregon, in more recent years worked in an area west of the present Clarno State Park. This area produced fauna fossils of the Clarno Formation which had not been previously uncovered.

During the approximately 100 years of fossil collecting and research in this area, more than 120 fossil mammal have been identified. They range in size from very small mice to huge rhinoceros and oreodonts. Fossil snails have also been collected.