Abstract

Bedrock within the Burgess Junction Quadrangle ranges from Precambrian through Jurassic. Scattered Tertiary and Quaternary deposits overlap the older rocks. Oligocene White River Formation and adjacent Quaternary pediments are aligned to suggest a post-Eocene, pre-Pleistocene fluvial drainage channel. The quadrangle is dominated by a large monocline which terminates a series of folds near the northeast corner of the map area. Extension of the Tongue River Lineament, largely a zone of folding, is chiefly a southwest-trending monocline. The north block of the Tongue River Lineament is characterized by folds oriented nearly perpendicular to the monocline. Drape folds over individually tilted basement blocks account for the major folds, the Dry Fork Anticline and the Fool Creek Syncline. Minor folds are produced from compression between adjacent folds on the subsided eastern corner of the Fool Creek block. Apparent disappearance of the Tongue River Lineament at the western edge of the Burgess Junction Quadrangle suggests that the rotational axis of a presumed Tongue River basement fault, separating the northern and middle divisions of the mountain range, is directly west-southwest of the map area.