G. 118.7
Munro Area, John Day Fossil Beds State Park. The valley of the John Day River has been widened to nearly five miles by erosion in the John Day Formation. Large tilted slide blocks of the John Day Formation and basalts jumbled together show how important landsliding of soft beds under hard rocks can be in widening valleys.
Fig. 6.—Sheep Rock from Thomas Condon viewpoint.
Here one can appreciate the regularity and extent of basalt flows of the flood or plateau type, which form the Columbia Plateau. Individual flows have been traced 100 miles. Travelers will see few other rocks between here and The Dalles, Wenatchee, Pendleton, or Spokane as they cross parts of the Columbia Plateau.
H. 116.2
Cathedral Rock. The bluff called Cathedral Rock is the front face of a large block of the John Day Formation that has slid from the west ([Fig. 7]). Inside the next horseshoe bend downstream a large mass of basalt is tilted down against Cathedral Rock. From the highway 1.1 miles farther north one can see the side of the tilted block along the river, and the same two prominent red and olive-drab ash layers in the high bluff from which the block slid. The horseshoe bend was formed as the river was pushed eastward by the nose of the landslide.
Fig. 7.—View of Cathedral Rock and diagram of landsliding.
