Note:

• The illustration (relying on cover image at Amazon 2016-12-18) is "Lunar Landscape" by the writer, titled along the bottom in Elvish script. It is one of five interior illustrations in the 1st US ed. (Houghton Mifflin, 1998), there as a plate facing p42.
• "Lunar Landscape" was first published in J.R.R. Tolkien: Artist and Illustrator (1995), where editors Scull and Hammond "discussed these illustrations at length"; namely, all five Roverandom illustrations by the writer. --from the 1st US ed. (Houghton Mifflin, 1985), primarily pp. xx-xxi of Introduction (Roverandom)

Synopsis: Black line finished in coloured pencil, relatively true to the text, "It presumably depicts the moment when Roverandom and the Man-in-the-Moon, returning from their visit to the dark side, see 'the world rise, a pale green and gold moon, huge and round above the shoulders of the Lunar Mountains' (p. 46)." --Introduction, cited above