Read this: The fauna in the state is just as diverse as the flora and varies greatly due to the large contrast in climates. In the mountain zone of the state the most observed mammals are: Mexican fox squirrel (Sciurus nayaritensis), antelope jackrabbit (Lepus alleni), raccoon (Procyon lotor), hooded skunk (Mephitis macroura), wild boar (Sus scrofa), collared peccary (Pecari tajacu), white-tailed deer (Odocoileus virginianus), mule deer Odocoileus hemionus, American bison Bison bison, cougar (Puma concolor), eastern cottontail Sylvilagus floridanus, North American porcupine Erethizon dorsatum, bobcat Lynx rufus, Mexican wolf Canis lupus baileyi, and coyote Canis latrans. American black bear Ursus americanus is also found but in very small numbers. The Mexican wolf, once abundant, has been extirpated. The main cause of degradation has been grazing. Although there are many reptilian species in the mountains the most observed species include: Northern Mexican pine snake, Pituophis deppei jani, Texas horned lizard (Phrynosoma cornutum), rock rattlesnake (Crotalus lepidus), black-tailed rattlesnake (Crotalus molossus), and plateau tiger salamander Ambystoma velasci, one of possibly many amphibians to be found in the mountains.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): The main cause of degradation has been what?
grazing