Cinder cones along the east and west sides of the Iskut River produced at least 12 basaltic lava flows in the last 70 000 years. The lava flows commonly have clinkery surfaces and locally preserved lava-flow features. Several of the Iskut River lava flows were large enough to block the river, which has subsequently cut down through the lava flows to form the Iskut River canyon, an extremely rugged, narrow gorge that has blocked the migration of salmon into the upper reaches of the Iskut River. The youngest Iskut River lava flows have not been dated successfully, but are younger than a flow dated at 2555 radiocarbon years before present. Several other young lava flows (<100,000 years old), which have not been dated directed, occupy tributary valleys of the Iskut River, including Snippaker Creek, Tom McKay Creek, King Creek, and Second Canyon. In the mid-1980s, the Iskut River canyon was studied as a possible site for a hydroelectric project. However, the project was abandoned in part because of the uncertain volcanic future in the area. Hazards associated with future eruptions in this unpopulated region are minor.