See the context of this sign.

Ancient Lake Morse

Thousands of years ago, a great ice sheet
from Canada flowed south through the
Puget Sound and west through the Strait
of Juan de Fuca. The ice sheet abutted
alpine glaciers flowing from the Olympic
Mountains. As warming occurred,
meltwater from mountain glaciers was
dammed by the ice sheet, forming ancient
Lake Morse. Continued warming caused
the ice sheet to withdraw, draining
the lake.

Morse Creek now parallels the road. In
ancient times it flowed over a ridge of soft
sediments connecting Blue and Round
Mountains. When glaciers dammed the
creek, it was diverted to a new path
between Round Mountain and the present
road, cutting through hard lava rocks. The
resulting gorge is visible as your drive
down the road or from the short trail at the
Tunnels parking area.

Don't miss the rest of our virtual tour of Olympic Mountains National Park in 646 images.