The term "desiccated" only means dried up or absent of water. They are no more "exciting" than any other kind of mountain, but that's not really the point of the author of Into the Beautiful North.
The story is told from the point of view of Nayeli, a young woman whose idealism and hope lead her to take a journey in an attempt to save her village from lawless thugs. Nayeli's story is part of a literary tradition called a "quest narrative" (among other things). Quest stories are everywhere around us. Humans have been telling these stories for thousands of years right up until today.
Star Wars is a quest, as are the King Arthur legends, The Odyssey, and Avengers: Infinity War.
Quest stories are almost always about finding someone or something that will make life better for our characters or, in some cases, save the world. Nayeli sees a great quest movie from the sixties, The Magnificent Seven, which tells the story of a character who goes in search of a group of legendary heroes to save the village from evil men who are terrorizing the people. Nayeli identifies with the movie and sets out to do the same thing: save the people she loves.
The importance of the desiccated mountains is not the mountains themselves. For Nayeli, they represent a world she has never seen, a world she has dreamed about her entire life, the United States. Early in the story, she reveals that she and Tacho, the cook, climb up on the restaurant roof and imagine that the clouds are the Manhattan skyline.
The mountains, the clouds, and the movie represent hope and opportunity for Nayeli, much as they do for many Mexican immigrants.