[Illustration: The town of John Day, the John Day River valley, and the
Strawberry Range, looking south and southeast. The tailings piles left
by gold dredges have been levelled for building sites since the
photograph was taken in 1946.]
One of the Pacific Northwest’s most notable outdoor recreation areas,
the “John Day Country” in northeastern Oregon, is named after a native
Virginian who was a member of the Astor expedition to the mouth of the
Columbia River in 1812.
There is little factual information about John Day except that he was
born in Culpeper County, Va. about 1770. It is known also that in 1810
this tall pioneer “with an elastic step as if he trod on springs” joined
John Jacob Astor’s overland expedition under Wilson Price Hunt to
establish a vast fur-gathering network in the western states based on a
major trading post at the mouth of the Columbia River.
The expedition arrived in the vicinity of the Grand Tetons, in what is
now Wyoming, in September 1811, and with the onset of winter met
disaster along the Snake River. When they ran out of food near the
present site of Twin Falls, Idaho, Hunt divided the expedition into four
parties to seek food and a feasible route through the canyons. As
described in Washington Irving’s _Astoria_, the party that included John
Day became widely separated from the others; experienced terrible
hardships while wintering with Indians near Huntington; and was
eventually reduced to just John Day and Ramsey Crooks. By mid-April of
the following year, Day and Crooks reached the junction of the Columbia
and Mah-hah Rivers, where a band of Indians took everything they had,
including their clothes. Because of this incident, the Mah-hah River was
renamed the John Day. Returning up the Columbia to seek help from
friendly Indians, they were rescued by a party of trappers in canoes,
and finally reached Astoria on the 11th of May 1812.
Although the first discovery of gold in Oregon reportedly was made in
1845 on one of the upper branches of the John Day River by a member of
an immigrant train, the settlement of the John Day Country really began
in 1862, when gold was discovered in Canyon Creek just above Canyon
City. Since then, possibly $30,000,000 worth of gold has been mined,
mostly from gravels in and along Canyon Creek and along a 10-mile
stretch of the John Day River. Lumbering and ranching are now the
principal industries of the region.
The growth of tourism in Oregon and Grant County and the accompanying
increase of interest in geology have stimulated the preparation of this
leaflet. The Grant County Planning Commission and State Department of
Geology and Mineral Industries have cooperated most cordially in the
program to better inform interested visitors about the geology of the
country they are seeing.
_GEOLOGIC HISTORY_
The John Day Country of today covers an area of 4,000-5,000 square miles
in the southwestern part of the Blue Mountain region of Oregon, and is
in the borderland between two major geologic provinces. One, to the
north, is the Columbia Plateau which consists of flat or gently tilted
flows of basalt covering about 100,000 square miles. The other, to the
south, is the Basin and Range Province which extends into Mexico, and is
characterized by a wide variety of complexly folded and faulted rocks.
The Strawberry-Aldrich Mountain Range, rising from 7,000 to 9,000 feet
in altitude along the south side of the John Day River valley (see
Figure 13 on page 21), is part of a 150-mile long, east-trending
mountain chain that locally separates the two provinces.
Many features that record events in the geologic history of northeastern
Oregon may be seen in the rocks along the paved highways within the John
Day Country. A road log describing some of these features is included as
a part of this booklet. The locations of principal points of interest,
keyed in the road log to state highway mile posts, are shown on the map
accompanying the road log.
The known part of the geologic history of the John Day Country began
with lava flows and deposition of volcanic ash, sandstone, shale, and
small lenses of limestone in a late Paleozoic sea more than 250 million
years ago. Sometime between 200 and 250 million years ago, peridotite
and gabbro (dark, magnesium-rich varieties of igneous rock) rose from
great depths and, as molten material (_magma_), invaded the preexisting
marine deposits. These igneous rocks now form the core of Canyon
Mountain and can be seen along the precipitous walls of Canyon Creek.
Masses of chromium ore (_chromite_) were carried upward with the molten
material. After erosion had exposed the peridotite and gabbro, the area
was submerged again and, during Late Triassic and Early Jurassic time
(about 180 million years ago), the Aldrich Mountain area was part of a
seaway into which lavas flowed. Thousands of feet of volcanic ash from
active volcanoes accumulated in the sea, and between eruptions great
thicknesses of mudstone and shale were deposited. The cuts along U. S.
Highway 395 between Canyon Creek and Bear Valley are in these rocks.
During part of this volcanic activity, Canyon Mountain stood as a high
landmass, but finally it too was deeply buried. Again the region emerged
and probably was dry land during the last half of Jurassic time (135 to
150 million years ago).
In Early Cretaceous time, molten material was intruded to form the
granitic rocks in the Aldrich Mountains and near Dixie Butte, northeast
of Prairie City. The gold veins in Canyon Mountain and in most of the
Blue Mountain region probably were formed at that time by solutions from
the granitic magma. Scattered patches of fossiliferous sandstone and
conglomerate like that in Goose Rock (see Figure 5 on page 10) show that
the sea encroached on the Blue Mountain region briefly during Cretaceous
time after erosion had exposed the granites. The shoreline was not far
east of the John Day area.
For the past 60 million years, eastern Oregon has been a land of
volcanoes, mountain building, and erosion. After the retreat of the
Cretaceous sea and an undefined period of erosion, volcanic eruptions
from widely scattered centers during the Eocene Epoch buried the region
under several thousand feet of volcanic rocks which now form the Clarno
Formation; locally these rocks consist mostly of andesitic lava flows
and coarse mud-flow breccias. The Clarno Formation was extensively
folded and faulted and deeply eroded before another series of volcanoes
in and somewhat east of the Cascade Mountains erupted rhyolitic ash that
was blown eastward and deposited as the John Day Formation during the
Oligocene Epoch. The John Day Formation appears to have been restricted
to a lowland area which geologists today call the John Day basin,
located between the present site of the Cascade Mountains and the
ancestral Blue Mountains. The Clarno and John Day beds in this basin are
world famous, having yielded thousands of bones, leaves, and pieces of
petrified wood that were buried and preserved by the volcanic ash in a
manner similar to the burial of Pompeii by the eruption of Mt. Vesuvius
in 79 A. D. Archaic large mammals such as the titanotheres, and small
ancestors of modern mammals such as the 4-toed forest horse _Eohippus_,
which was the size of a fox terrier, roamed subtropical forests during
the Eocene Epoch. Many important links in the evolutionary chain of
mammals have been found in the John Day fossil beds; for example, the
3-toed horse _Mesohippus_, which was a forest dweller the size of a
sheep, had teeth for browsing instead of grazing.
The modern day landscape began to take form in Middle Miocene time, when
the basalt flows which cover most of the area and are exposed in the
walls of Picture Gorge (hence their name, Picture Gorge Basalt) buried
the landscape formed on the John Day Formation and older rocks. The
basalt erupted from long cracks or fissures in the Earth’s crust and
formed floods of very fluid lava which flowed for distances up to one
hundred miles. These basalts are recognized by geologists to be of a
distinct type, commonly called plateau or flood basalt. Basalt, frozen
in the fissures, forms dikes that commonly weather out above the
adjoining softer rocks, as shown in the picture of Kimberly Dike on page
16.
While the Picture Gorge Basalt was flooding most of the John Day basin,
several volcanoes in the vicinity of Strawberry Mountain erupted
andesitic to rhyolitic lava and ash, and built up cones similar to Mt.
Hood and the other high peaks of the Oregon Cascades. Geologists have
named the remnants of these cones the Strawberry Volcanics. Because
these volcanoes rose several thousand feet above the top of the Picture
Gorge Basalt, ash and erosional debris from them washed out over the
basalt; these materials constitute the Mascall Formation. Although the
mountains were timbered, the lowlands probably were open and grassy.
Bones and teeth of a pony-size three-toed horse, _Merychippus_, have
been dug from the Mascall Formation. When the eruptions ceased in Early
Pliocene time (about 10 million years ago), the entire Blue Mountain
region probably resembled the eastern part of the Cascade Mountains in
Oregon today, particularly the area between Mt. Hood and Crater Lake.
The present Strawberry-Aldrich Mountain range and the ridges and valleys
north of it were formed when the Earth’s crust buckled and broke under
strong compressive forces from the north and south. Partly by bending or
folding, and partly by breaking along the John Day and other faults, the
Strawberry-Aldrich Mountains were gradually raised a mile and a half to
two miles above the valley to the north. The floor of the main John Day
River valley was filled with gravels eroded from the rising mountains
and, as the folding and faulting and erosion slowed, an extensive,
broad, gently sloping surface was formed on top of the valley fill.
While these gravels (called the Rattlesnake Formation) were
accumulating, however, a great volcanic eruption spread an ash flow more
than 100 feet thick over the entire length of the John Day valley floor;
remnants of this flow form prominent rim-rocks between the town of John
Day and Picture Gorge. Bones of _Hipparion_, a horse the size of a pony
which had feet and teeth like modern horses, have been found in the
gravels under the ash flow.
_THE PRESENT LANDSCAPE_
Differences in the rates of erosion of various rocks were as important
as folding and faulting in forming the topographic features in the John
Day Country. The chief agents of erosion are chemical weathering
processes that eventually break down or decompose all rocks, and running
water which carries away the weathered or partly weathered and broken
material. Picture Gorge is narrow because the basalts in the walls are
very resistant to weathering and break along vertical joints into large
blocks that do not move easily. In contrast, the John Day River has cut
a broad, flat-floored valley in the Mascall Formation at the south end
of Picture Gorge because the ashy beds weather to fine clay which is
easily washed away.
Landslides have marked the face of the John Day Country. Large rock
masses commonly slide where steep cliffs form in soft rocks that are
capped by hard resistant rocks. When the cliff face becomes too high and
steep, the soft beds give way and large blocks or masses slide downward,
usually tilting backward as they move, as shown in the diagram of
Cathedral Rock on page 15. Cathedral Rock and two small landslides north
of the river, about two miles east of John Day, show this classic form.
Many landslides, however, are just jumbled, hummocky masses of slumped
material. Large-scale landsliding in the John Day Formation under the
Picture Gorge Basalt is colorfully displayed along the river for 8 miles
north of Picture Gorge. Some landslides occur suddenly, but many move
forward only as fast as the toe or lower end is eroded away, as at
Sunken Mountain.
Glaciers have sculptured the principal valleys that lie above an
altitude of about 5,000 feet. Moving ice, hundreds of feet thick,
plucked out semi-circular amphitheaters called _cirques_ at the heads of
the valleys. The 2,000-foot cliffs above Little Strawberry Lake were
formed this way. Rocks held in the ice, like the teeth of a giant rasp,
ground off irregularities and widened the valley bottoms to a broad U
shape as the glaciers moved down the valleys. The effectiveness of ice
scour can be seen by comparing glaciated Strawberry Creek above
Strawberry Lake (as shown in figure 15 on page 22) with unglaciated
Picture Gorge or with Canyon Creek just above Canyon City.