The country now became rugged and broken. High bluffs advanced upon the
river, and forced the travellers occasionally to leave its banks and
wind their course into the interior. In one of the wild and solitary
passes they were startled by the trail of four or five pedestrians, whom
they supposed to be spies from some predatory camp of either Arickara
or Crow Indians. This obliged them to redouble their vigilance at
night, and to keep especial watch upon their horses. In these rugged
and elevated regions they began to see the black-tailed deer, a
species larger than the ordinary kind, and chiefly found in rocky and
mountainous countries. They had reached also a great buffalo range;
Captain Bonneville ascended a high bluff, commanding an extensive view
of the surrounding plains. As far as his eye could reach, the country
seemed absolutely blackened by innumerable herds. No language, he says,
could convey an adequate idea of the vast living mass thus presented to
his eye. He remarked that the bulls and cows generally congregated in
separate herds.

Opposite to the camp at this place was a singular phenomenon, which
is among the curiosities of the country. It is called the chimney. The
lower part is a conical mound, rising out of the naked plain; from the
summit shoots up a shaft or column, about one hundred and twenty feet
in height, from which it derives its name. The height of the whole,
according to Captain Bonneville, is a hundred and seventy-five yards.
It is composed of indurated clay, with alternate layers of red and white
sandstone, and may be seen at the distance of upward of thirty miles.

On the 21st, they encamped amidst high and beetling cliffs of indurated
clay and sandstone, bearing the semblance of towers, castles, churches,
and fortified cities. At a distance, it was scarcely possible to