For the next two miles, to the Sunken Mountain viewpoint, the road winds through landslides in the John Day Formation and Picture Gorge Basalt. [Illustration: Fig. 10.—Ancient landscape on John Day Formation buried under Picture Gorge Basalt.] P. 22.0 _Sunken Mountain._ A small landslide in the lower part of the John Day Formation is called Sunken Mountain. When the valley wall was over-steepened by normal stream erosion, the jumbled material in the lower part broke away and slid down from the steep bare slopes above. Absence of tilted trees indicates that the slide is not very active now. The bare “badland” slopes are being eroded by rain wash. The cliffs of the John Day Formation, which the road climbs half a mile farther east, are the result of rapid but normal headward erosion by the creek. Eventually, because of its lower elevation and steeper gradient, this branch of Cottonwood Creek will intercept and behead Deer Creek just east of Hamilton. A photogenic perspective view of the future stream piracy can be seen from the road on the ridge just south of Sunken Mountain, about a mile and a half from the highway. Q. 26.4 _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.] R. 99.5 _Fox Valley._ Down-warped flows of Picture Gorge Basalt dip toward Fox Valley from all sides to form a basin (Fig. 12). The valley is eroded out of ashy beds and gravels of the Mascall Formation which fill the center of the basin to an estimated depth of 1000-1200 feet. Faults form parts of the northern and southern borders of the basin. The straight, timbered, northward-facing steep slope less than a mile southeast of the viewpoint marks a fault. S. 180.3