The thinner walls are composed of a single depth of the parallelopiped, while the thicker ones consist of two or more depths.
These walls pass the river at several places, rising from the water's edge much above the sandstone bluffs, which they seem to penetrate; thence they cross in a straight line, on either side of the river, the plains, over which they tower to the height of from ten to seventy feet, until they lose themselves in the second range of hills.

Sometimes they run parallel in several ranges near to each other, sometimes intersect each other at right angles, and have the appearance of walls of ancient houses or gardens." The wall-like, canyon formations were charted by Lewis and Clark as "The Stone Walls." Their fantastic outlines have been admired and described by modern tourists, and some of them have been named "Cathedral Rocks," "Citadel Rock," "Hole in the Wall," and so on.
Passing out of this wonderful region, the expedition entered upon a more level country, here and there broken by bluffy formations which extended along the river, occasionally interspersed with low hills.

Their journal says: "In the plains near the river are the choke-cherry, yellow and red currant bushes, as well as the wild rose and prickly pear, both of which are now in bloom.

From the tops of the river-hills, which are lower than usual, we enjoyed a delightful view of the rich, fertile plains on both sides, in many places extending from the river-cliffs to a great distance back.

In these plains we meet, occasionally, large banks of pure sand, which were driven apparently by the southwest winds and there deposited.