Revelstoke (population 10,000) lies at the confluence of the Illecillewaet and Columbia Rivers in southern British Columbia (51°N, 118°12' W);and is 435 mi(700 km) east of Vancouver, British Columbia, and 250 mi (400 km) west of Calgary, Alberta (Fig.1). Principal access is by the Trans-Canada Highway and Canadian Pacific Railway. Provincial highways, secondary, and logging roads provide access to many geologically significant localities throughout the area (Brown and others,1981). The Big Bend Highway (British Columbia 23) runs northward from the Trans-CanadaHighway, past Revelstoke Dam 3 mi (5 km) north, to Mica Dam 96 mi (155 km) north.