A Neocene Erosion Surface in Central Oregon

Abstract

A landscape, in the old age stage, termed the Ochoco Erosion Surface, bevels the Columbia lavas and Mascall formation of middle Miocene age at a large angle, and the Rattlesnake lower or middle Pliocene at a small angle, in parts of the Ochoco Range and the John Day country of central Oregon. North of the John Day country the Condon Erosion Surface, locally at least a peneplane, probably but at present not demonstrably the correlative of the Ochoco, truncates the Columbia lavas and perhaps The Dalles formation. A pause in the eventful diastrophic history of this part of the Northwest is apparently indicated by these features. Subsequently, during the present or Dayville cycle, the great gorges and valleys have been excavated.