_Thomas Condon Viewpoint, John Day Fossil Beds State Park._ From Picture
Gorge to the cliffs opposite, the Picture Gorge Basalts and varicolored
ash beds of the John Day Formation rise together nearly 2000 feet. The
basalt that caps Sheep Rock is an erosional remnant. The lower beds in
the John Day Formation are colored red by clay eroded from thick soil on
the Clarno Formation, which is exposed in the farthest red hill. The
soil was formed by tropical weathering some 30-35 million years ago,
before the John Day Formation was laid down. Faulting on a small scale
is illustrated in Sheep Rock, where the thick olive-drab ash flow in the
middle of the John Day Formation is offset 75-100 feet (Fig. 6). The
fault slopes about 45° eastward. About two miles downstream, large-scale
movement on two faults has dropped the basalt flows in Middle Mountain
2000-2500 feet. One of the faults follows along the upstream base of
Middle Mountain (Fig. 6).
[Illustration: Fig. 5—North-south section along the John Day River
through Picture Gorge and Middle Mountain.]
[Illustration: Fig. 1.—Geologic map of the John Day Country showing log
route.]
[Higher-Resolution Map]