Geology Reference
In-Depth Information
Multnomah Falls
The Colum-
bia River gorge is
lined with 71 water-
falls in 420 square
miles, 11 of which
are over 100 feet
high. Of these, Mult-
nomah Falls, which
is the fourth highest
falls in the United
States, drops, in what
is actually two falls, a distance of 620 feet over a
projecting ledge of Grande Ronde Basalt of the
Columbia River lavas. Waterfalls tend to be ephemeral
features, and most of those in the gorge may have
begun during recent glacial floods 13,000 years ago
when high waters cut back and carried away softer
valley alluvium leaving the streams to fall over the
more resistant basalt.
The Columbia River gorge has been intermittently
plugged by local lava flows and landslides through-
out the Pleistocene and Holocene (after Allen, 1979;
Tolan and Beeson, 1984; Anderson and Vogt, 1987).
