Metamorphism in the Riggins region, western Idaho

Mineral Resources of the Hells Canyon Study Area, Wallowa County, Oregon, and Idaho and Adams Counties, Idaho

“…Limestone of Triassic or possibly older age crops out on the west side and the crest of the ridge extending north from the Seven Devils Mountains, on the divide between the Snake and Salmon Rivers. Limestone is also exposed along the Rapid River in a belt that continues northeastward out of the study area at least 20 mi (32 km) (Hamilton, 1963b). Less extensive bodies of limestone are on Cannon Ball Mountain and on ridges to the north.…”

“…The following summary of the geologic history of the study area is based chiefly on the observations of Vallier (1967 and Hamilton (1963b). The earliest event for which firm evidence exists occurred during the Permian when basalt and andesite flows and volcaniclastic rocks were deposited.…”

“…Lindgren (1900) sketched the geology of a large region that includes part of the study area, and Wagner (1945) made a reconnaissance geologic map of the east-central part of the study area near Pittsburg Landing. Ralph S. Cannon and co-workers studied the metavolcanic and plutonic rocks in the southern part of the study area; their work was summarized by Hamilton (1963b). Hamilton (1963bHamilton ( , 1969) mapped most of the Riggins 30-minute quadrangle, which includes the southeastern part of the study area.…”

“…Ralph S. Cannon and co-workers studied the metavolcanic and plutonic rocks in the southern part of the study area; their work was summarized by Hamilton (1963b). Hamilton (1963bHamilton ( , 1969) mapped most of the Riggins 30-minute quadrangle, which includes the southeastern part of the study area. These investigations and others by Hamilton (1960Hamilton ( , 1965 were concerned chiefly with foliated metamorphic and plutonic rocks that are extensively exposed to the east, and with Miocene basalt and Cenozoic structures (Hamilton, 1962(Hamilton, , 1963a.…”

“…1). The rocks are in the western fringe of a broad, north-trending belt of low-to highgrade metamorphic rocks along the Little Salmon and Salmon Rivers (Hamilton, 1963b). The terrane of metamorphic rocks is bounded on the west and separated from underlying limestone by a thrust fault.…”