Turner selected his "Mountainous" subjects from his sketches in Wales, the Scottish highlands and, most importantly, from the 400 he made during his one trip to Switzerland in 1802.

Turner said "the country on the whole surpassed Wales and Scotland . . . The weather very fine.  He saw some fine Thunderstorms among the Mountains."
-Joseph Farington, 1802

"The light must be sharp and brilliant, particularly upon the front trees, bones, rocks, &c . . . Be careful about the distance.  It wants air and light scraping to render it like the place."
-J.M.W. Turner to Charles Turner, 1809