_Long Creek Mountain._ An uplifted block of Picture Gorge Basalt
1400-1500 feet thick forms Long Creek Mountain; Round Basin is eroded in
the John Day Formation on which the basalt rests (Fig. 11). The base of
the basalt can be seen in road cuts on either side of Basin Creek. The
Hamilton fault follows the gulch to the left just below the parking
area, goes up the tree-filled gulch across Basin Creek, along the low
ridge at the northeast edge of Round Basin, and then along the northern
foot of the mountain. The small slab of basalt south of the fault in
Basin Creek has been tilted about 10° north by downward drag along the
fault. The Hamilton fault system extends about 15 miles farther east.
(In Long Creek turn right—south—on U. S. Highway 395).
[Illustration: Fig. 11.—View of Long Creek Mountain and Round Basin, and
diagram of the geologic structure.]
[Illustration: Fig. 12.—North-south section across Fox Valley, showing
the faulted basin structure.]