1911 Encyclopædia Britannica/Dalle
DALLE (pronounced “dal,” Fr. for a flag-stone or flat tile), a rapid falling over flat smooth rock surfaces in a river bed, especially in rivers flowing between basaltic rocks. The name is common in America, and came into use through the French employés of the Hudson’s Bay Company. Well-known “dalles” are on the St Louis, St Croix and Wisconsin rivers. The “dalles” of the Columbia river are very beautiful, and have given its name to Dalles (1910 pop. 4880), county-seat of Wasco county, Oregon.