Miles Canyon is well known to students of the Klondike Goldrush. It was here that the Yukon River began a stretch of rough and dangerous water, the Miles Canyon Rapids and shortly thereafter the Whitehorse Rapids. Many of the home made boats and rafts constructed by the would-be gold prospectors were destroyed or over-turned in these rapids, and many people lost their lives here. The presence of these rapids catalyzed the formation of the city of Whitehorse as a access point to the Yukon River (down-river from these rapids) and Dawson City.
A hydroelectric plant and dam have since been built near the site of the Whitehorse Rapids, which resulted in flooding and effacement of the Whitehorse Rapids and to a large extent the Miles Canyon Rapids as well. Today you'll find that the Yukon River moves quickly through the basalt cliffs of Miles Canyon, but that it is no longer particularly dangerous. Several canoes safely passed through the Canyon when I visited the site.
A bridge has been constructed over the river, and it is now a popular stop for tourists visiting the city. I hiked to the falls and enjoyed the natural beauty of the area.