Abstract

IGNEOUS FEATURES OF JUNIPER RIDGE, OREGON

BY JOHN ELIOT ALLEN*

A part of Juniper Ridge adjacent to the Squaw Butte Ranch, in Harney County, Oregon, discloses extrusive or shallow-intrusive masses of igneous rock with internal structures so complex that all features could not be mapped at a scale of 1000 feet to the inch. These features were studied in an area of about a square mile in sec. 36, T. 23 S., R. 25 E., and sec. 1, T. 24 S.

Rocks of five igneous types, all closely related, were discriminated in the mapping:

  • Porphyritic obsidian, light-gray; mostly as float.

  • Porphyritic obsidian, red; as dikes.

  • Perlitic obsidian, largely black but red in part, lithophysae abundant at many places; as small lenses.

  • Porphyritic andesite, gray or red and gray in fine bands; commonly has platy parting between bands, which are contorted at places.

  • Porphyritic andesite, dark-gray to reddish, massive, lithophysae abundant . . .

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