A small NW.-dipping thrust has caused the repetition of some of the lower Paleozoic beds where Trout Creek has cut a gap in the ridge of Paleozoic rocks in the SE. 1/4 of sec. 3, T.14S., R. 77W. The NE. trend and NW. dip of the thrust suggest that it is associated with the NE.-trending compressive structures that deform early Oligocene rocks along Mushroom Gulch 1 mi. S. Hence, the thrust probably formed during the late or post-Oligocene.