The correct answer is: A. 1500-3000 m.
Mountainous soil zones are found at elevations of 1500-3000 meters. These zones are characterized by thin, rocky soils that are poor in nutrients. The climate in these zones is cold and dry, with annual precipitation of 250-500 mm. The vegetation in these zones is sparse, consisting of grasses, shrubs, and low-growing trees.
Option B is incorrect because 6100 meters is the elevation at which the alpine soil zone is found. Option C is incorrect because 3000-6000 meters is the elevation at which the subalpine soil zone is found. Option D is incorrect because 1000-1500 meters is the elevation at which the montane soil zone is found.