entering the stretch of the river known as the Gates of the Mountains,
Meriweather Lewis writes on July 19, 1805:
"This evening we entered much the most remarkable cliffs
that we have yet seen. These cliffs rise from the waters
edge on either side perpendicular to the height of 1200 feet.
Every object wears a dark and gloomy aspect. The towering and
projecting rocks in many places seem ready to tumble on us.
The river appears to have forced its way through this
immense body of solid rock for the distance of 5 3/4 miles and
where it makes its exit below has thrown on either side vast
columns of rocks mountains high.
"The river appears to have worn a passage just the
width of its channel or 150 yards. It is deep from side to side,
nor is there in the first three miles of this distance a spot
except one of a few yards in extent on which a man could rest
the sole of his foot. Several fine springs burst out at the
waters edge from the interstices of the rocks. It happens
fortunately that although the current is strong it is not so
much so but what it may be overcome with the oars, for there
is here no possibility of using either the cord or setting pole.
It was late in the evening before I entered this place and was
obliged to continue my route until sometime after dark before
I found a place sufficiently large to encamp my small party.
At length, such an one occurred on the larboard side where we
found plenty of lightwood and pitch pine. This rock is a black
granite below and appears to be much lighter color above and
from the fragments I take it to be a flint of a yellowish brown
and light creamy-colored yellow. >From the singular appearance
of this place I called it the gates of the rocky mountains."
rocks Lewis is describing ( shown left and right) are the Mississippian
Madison Limestones exposed in the footwall of the Eldorado-Lewis
Thrust system in the Montana Thrust Belt. Farther upstream, the
Geotour will also examine the Precambrian Belt Series rocks thrusted
over the Madison and exposed in the hanging wall of the thrust.
Lewis describes the limestones as being dark and foreboding, which
is probably a result of his seeing the rocks initially in the
deep canyon in the early evening after a rain storm, which tends
to make the rocks look darker.