Just south of Angastaco, the rutted earthen highway that is RN 40 weaves through surrealist rock formations that are unofficially called the Angastaco Natural Monument. The views are stunning. Expect jagged mineral-streaked mountains laced with sandy desert trails, pockmarked rock formations ideal for bouldering, and countless viewpoints and potential campsites. Look for handmade wooden signs, fashioned by locals, which point out features (in Spanish) along the scenic drive.
This is arguably the most beautiful section of the Valles Chalcaquíes, and that's saying something.