The passes allowed the barrier to be crossed without ascending for the higher ridges.

There are many of these canyons, or steep valleys, more or less narrow, through which they could glide, such as Bridger Gap, through which runs the Pacific Railway into the Mormon territory, and others to the north and south of it.
It was through one of these that the "Albatross" headed, after slackening speed so as not to dash against the walls of the canyon.
The steersman, with a sureness of hand rendered more effective by the sensitiveness of the rudder, maneuvered his craft as if she were a crack racer in a Royal Victoria match.

It was really extraordinary.
In spite of all the jealousy of the two enemies of "lighter than air," they could not help being surprised at the perfection of this engine of aerial locomotion.
In less than two hours and a half they were through the Rockies, and the "Albatross" resumed her former speed of sixty-two miles an hour.
She was steering southwest so as to cut across Utah diagonally as she neared the ground.

She had even dropped several hundred yards when the sound of a whistle attracted the attention of Uncle Prudent and Phil Evans.

It was a train on the Pacific Railway on the road to Salt Lake City.
And then, in obedience to an order secretly given, the "Albatross" dropped still lower so as to chase the train, which was going at full speed.