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I I I I I I I I I I I I I I I I I I I , 1l0112~ 1 evel s of Pl ei stocene pediments and terrace deposi ts occur along the Whi te River and its larger tributaries. The upper part of the study area had extensi ve 1 andsl i de activi ty duri ng the Pl ei stocene Epoch. Mass sl umpi ng has Occurred near the limits of the basalt flows. The youngest deposits in the region are of the Holocene Epoch of the Quaternary Peri od and are characteri zed by recent all uvi al sand and gravel, landslides, colluvium, and talus. 3;3 Seismicity The Whi te River study area is wi thi n Area 1 on the sei smic ri sk map of the western United States. Structures in Area 1 can be expected to suffer minor damage in the event of an earthquake. The closest recorded significant earthquakes in the region were in the vicinity of Rangely, Colorado, 50 miles to the west of the study area. They were associated with secondary recovery in the neighboring oil field during the 1960's. Six seismic events were recorded between 3.7 and 4.6 on the Richter scale, and one of IV on the Mercall i seal e. The strongest recent earthquake wi thi n a 200-mil e radi us of the area occurred October 11, 1960 and had a modified Mercalli intensity of VI. The epicenter was near the town of Ridgeway in Ouray County, Colorado. Several other earthquakes have been recorded in the area, two with an intensity of V. The earthquake activity in the Ridgeway area is probably associated with tectonic activity and associated faults in the Uncompahgre Uplift. An earthquake of Merca11i intensity VII in 1901 was reported to have caused damage northeast of Gunnison, Colorado. On November 7, 1882, an earthquake with an estimated intensity between V and VI occurred in Colorado. There is lack of agreement as to the location of the epicenter. Some analysts have placed the epicenter in northwest Colorado; others indicate Grand Junction or even Oenver. 3-3