Agreed.
On the left pic there's spruces, and what might be blue stem goldenrod.
Goldenrod is what I thought of as well, but that blooms in late summer through fall.
This article says he visited "in the recent days" - published May 27, 2013.
Date stamp of May 28, 2013 on bottom left pic.
If it's not goldenrod what blooms in late May in desert areas that is yellow?
Billboard is interesting, but hard to tell.
Good question.