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 . . .