the steeply sloping face of the terrace, but after a few feet the
trunks bend upward and stand vertically. Clearly when these trees
were young the terrace was not there. Then an earthquake came.
One block of the earth's crust was dropped down while another was
raised up. Along the dividing line a terrace was formed. The
trees that happened to stand along the line were tilted and left
in a slanting position on the sloping surface between the two
parts of the earth's crust. They saw no reason to stop growing,
but, turning their tips toward the sky, they bravely pushed
upward. Thus they preserve in a striking way the record of this
recent movement of the earth's crust.

Volcanoes as well as earth movements have occurred on a grand
scale within a few hundred years in the cordillera. Even where
there is today no visible volcanic activity, recent eruptions
have left traces as fresh as if they had occurred but yesterday.
On the borders of the Grand Canyon of the Colorado one can see
not only fresh cones of volcanic ash but lava which has poured
over the edges of the cliffs and hardened while in the act of
flowing. From Orizaba and Popocatepetl in Mexico through Mount
San Francisco in Arizona, Lassen Peak and Mount Shasta in
California, Mount Rainier with its glaciers in the Cascade Range
of Washington, and Mount Wrangell in Alaska, the cordillera
contains an almost unbroken chain of great volcanoes. All are
either active at present or have been active within very recent
times. In 1912 Mount Katmai, near the northwestern end of the
volcanic chain, erupted so violently that it sent dust around the
whole world. The presence of the dust caused brilliant sunsets
second only to those due to Krakatoa in 1883. It also cut off so
much sunlight that the effect was felt in measurements made by