This was the primary route west for pioneers who relied on the Humboldt River. It appears as a horizontal dark area and grove of trees at far right.

The semi is a very lucky shot. It is heading west on I-80 past an interpretive center devoted to the western migration, largely from 1840-69, when the Transcontinental Railroad was finished.

Nevada was a long tough stretch and many pioneers had to discard belongings to lighten the load for their exhausted animals. Some areas were littered with belongings, as shown here. Info: http://www.californiatrailcenter.org