The greatest danger to most park visitors is due to altitude. The entire park is above 7,500 feet and ranges as high as 14,259 feet, so it is important to take time to acclimate before undertaking strenuous activities. Even driving at high elevation can affect sensitive individuals. Altitude sickness symptoms include shortness of breath, fatigue, dizziness, nausea, rapid heartbeat and insomnia. Also note that high elevation increases the chance of dehydration, severe sunburn, and the aggravation of pre-existing medical conditions. Drink several quarts of water per day to ward off dehydration. Wear and reapply sunscreen often. If you begin to feel sick or experience any physical problems descend to lower elevations.
Be aware of the weather. A bright, sunny day can turn windy and wet within a matter of minutes with high winds and driving rain or snow. Be prepared for changing conditions by dressing in layers and always carrying gear appropriate for both cold, wet weather and bright, sunny conditions. If caught in a lightning storm above treeline get away from summits and isolated trees and rocks and find shelter (but avoid small cave entrances and overhangs) and crouch down on your heels.
Other park dangers include wildlife – never feed wild animals, and always give them their space. Animals are unpredictable, particularly if they feel threatened, and even a deer is capable of killing a human. To protect against larger predators like bears and mountain lions make noise while hiking to avoid startling an animal, and use bear-proof containers to store anything with a scent; this includes food, toothpaste, deodorant, empty food wrappers, or anything else that might attract a bear’s interest.
Park streams may contains giardia and other water borne diseases, so always purify water before drinking. Be careful on snowfields, particularly on steep slopes where avalanche dangers may be high.