In 1992, I sent a letter to the New York Times Book Review that quoted
the "Voices out of Utah" section of Mark Twain's "The Dervish and the
Offensive Stranger" to argue that he addressed the issues of ecological
and multicultural conflict in the West that were being highlighted in the
early 1990s by what were called "new" or "revisionist" historians. See:

Don't Fence Them In
http://query.nytimes.com/gst/fullpage.html?res=9E0CEFDA1431F93BA2
5753C1A964958260

His writings about environmental issues were not limited to descriptions
of scenery. For example, chapter 19 of Following the Equator includes
this discussion of the dingo:

"In that garden I also saw the wild Australian dog -- the dingo.  He was a
beautiful creature -- shapely, graceful, a little wolfish in some of his
aspects, but with a most friendly eye and sociable disposition.  The
dingo is not an importation; he was present in great force when the
whites first came to the continent. It may be that he is the oldest dog in
the universe; his origin, his descent, the place where his ancestors first
appeared, are as unknown and as untraceable as are the camel's. He is
the most precious dog in the world, for he does not bark. But in an evil
hour he got to raiding the sheep-runs to appease his hunger, and that
sealed his doom. He is hunted, now, just as if he were a wolf. He has
been sentenced to extermination, and the sentence will be carried out.
This is all right, and not objectionable. The world was made for man --
the white man."

Dan Beard's illustration for this passage, "The White Man's World,"
shows a white soldier standing amid dead animals and people. Twain's
writings on the environmental impact of imperialism can be traced back
to his 1866 trip to Hawaii which resulted in his first commentaries on the
"disease of civilization."

Jim Zwick