Geological Survey Bulletin 1161-D Geologic Reconnaisance of the Antelope-Ashwood Area, North-Central Oregon

Cover

Abstract

Introduction

Stratigraphy

Pre-Tertiary rocks
Clarno Formation
John Day Formation
     Lithology
     Welded ash flows
     Age and correlation
     Source of the volcanic material
Columbia River Basalt
Dalles Formation
Basalt of Pliocene or Pleistocene age
Quaternary loess, landslide debris, and alluvium
Intrusive rocks

Structure

Friday agate deposit

References cited

1. Reconnaissance geologic map of the Antelope-Ashwood area and geologic map and section of the area between Willowdale and Ashwood (omitted from the online edition)

1. Index map of part of north-central Oregon

2. Generalized columnar section of the John Day Formation

3. Rhyolite dome in the lower part of the John Day Formation

4. Photomicrograph of a soda sanidine crystal partly rimmed by myrmekitic intergrowths of quartz and sanidine

5. Columnar-jointed ash-flow sheet

6. Lithophysae in a welded ash-flow sheet

7. X-ray diffraction charts of volcanic glass that is partly devitrified to cristobalite and alkalic feldspar

8. Spherulite-bearing ash flow of the John Day Formation at the Friday agate deposit

1. Bedded rocks of the Antelope-Ashwood area, north-central Oregon

2. Chemical analyses and norms of rocks from the John Day Formation near Ashwood, north-central Oregon

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UNITED STATES DEPARTMENT OF THE INTERIOR
STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY
Thomas B. Nolan, Director

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