2448, RAFT RIVER MOUNTAINS FAULT

Structure number: 2448. Comments: Hecker's (1993) fault number 6-17. Structure name: Raft River Mountains fault. Comments: Synopsis: Poorly understood middle to late Pleistocene(?) fault in the Raft River Mountains. The fault is in both Utah and Idaho. Date of compilation: 10/99. Compiler and affiliation: Bill D. Black (Utah Geological Survey) and Suzanne Hecker (U.S. Geological Survey). State: Utah. County: Box Elder. 1° x 2° sheet: Brigham City. Province: Basin and Range. Reliability of location: Poor. Comments: Mapped by Compton (1972) and Doelling (1980). Mapping from Doelling (1980). Geologic setting: North-trending normal fault near the Utah-Idaho border along the northeast side of the Raft River Mountains. The Raft River Mountains have a core of Precambrian metamorphic rocks and trend east-west, similar to the Uinta Mountains. Northern slopes of the mountains drain into the Snake River and are considered part of the Snake River Plain, rather than the Great Basin. Sense of movement: N. Comments: Dip: No data. Comments: Dip direction: E. Geomorphic expression: Faulted alluvium. Age of faulted deposits: Middle to late Pleistocene(?). Paleoseismology studies: None. Timing of most recent paleoevent: (4) Middle and late Quaternary (<750 ka). Comments: Recurrence interval: No data. Comments: Slip rate: Unknown, probably <0.2 mm/yr. Comments: Length: End to end (km): 2 Cumulative trace (km): 2 Average strike (azimuth): N1°E REFERENCES

Compton, R.R., 1972, Geologic map of the Yost quadrangle, Box Elder County, Utah and Cassia County, Idaho: U.S. Geological Survey Miscellaneous Investigations Series Map I-672, scale 1:31,680.

Doelling, H.H., 1980, Geology and mineral resources of Box Elder County, Utah: Utah Geological and Mineral Survey Bulletin 115, 251 p., scale 1:125,000.

Hecker, Suzanne, 1993, Quaternary tectonics of Utah with emphasis on earthquake- hazard characterization: Utah Geological Survey Bulletin 127, 2 plates, scale 1:500,000, 257 p.