This wooden sign near the parking area of the Dry Falls observation area reads,
Story of Dry Falls
These cliffs are skeletal remnants of what was once the world's
largest waterfall. They bear stark witness to the tremendous
power of catastrophic floods that swept over eastern Washington
at the end of the last ice age.
The falls began 20 mi. to the to the south, but receded upstream through
powerful erosive action. The retreat of the falls gave birth to
the canyon below. the lower Grand Coulee. With the enormous
force of the floodwaters spewing several cubic miles of rock
over vast areas downstream. Today Dry Falls remains as one of
the most spectacular geologic wonders of the age of ice.