The rapids acquired their name after a dark series of events in 1817, when a crew of North West Company voyageurs lost their canoes and food during a traverse of the rapids and were forced to attempt the overland journey to Spokane House, with only one survivor being rescued by local native people after a harrowing survival ordeal, and a confession of cannibalistic survival: Dalles des Morts [mis-spelled "Dalle de Mort" on Trutch's 1871 map of British Columbia.]
(from Douglas of the Fir: A Biography of David Douglas, Botanist, by A.G. Harvey; Harvard University Press, 1947, p.110) Source: Provincial Archives of BC "Place Names File" compiled 1945-1950 by A.G. Harvey from various sources, with subsequent additions [1] "In 1817 a party of seven Nor'westers was sent back to Spokane House [from Boat Encampment] because they were too ill to traverse the Rocky Mountains with the rest of the party.
The 1838 Express had had a difficult journey from Fort Edmonton, and the party contained an unruly upper-crust greenhorn who had eloped with one of the daughters of HBC Governor Simpson, who during an ill-advised transit of the rapids panicked and jumped from the canoe with his wife in his arms, upsetting the canoe in the process and resulting in the death of all but one who had been aboard, including himself and his wife but sparing Matooskie, a native woman in the party who had lost her child in the journey via Athabasca Pass.
During the Big Bend Gold Rush from 1865 on, the Dalles des Morts marked the head of steamboat navigation on a route that stretched from Marcus, Washington Terr.
Still others came to the goldfields on the longer route around the Big Bend from the East Kootenay and the Wild Horse Creek Gold Rush and Montana.
In the case of Dalles des Morts, the pun carries the extra weight of "gravestone", as that is the usual meaning of the phrase in French.