Mountain streams like to descend in stair-stepped series of short falls and brief pools. In these cascades, water alternates between two energy states, much like air shifting between super- and subsonic ﬂow. The white water of the falls is the ﬂuvial equivalent of a sonic boom. Cascade is used more broadly to mean a rocky stretch of whitewater less steep than a waterfall but steeper than a rapid. The Cascades of the Columbia River, formed several centuries ago when a massive slide ﬁlled the channel in the mid– Columbia Gorge, presented Lewis and Clark’s Corps of Discovery with a three-mile stretch of chutes and falls, “boiling in a most horriable manner,” according to William Clark’s journal. Rafting or boating the gorge was the last leg of the Oregon Trail for many early immigrants. Some lost all they owned to the Cascades, and some lost their lives. Now drowned in slackwater behind Bonneville Dam, this reach of river gave the Cascade Range its name.