High-Altitude National Parks: Avoiding Altitude Sickness

How Common Is Altitude Sickness in National Parks?

Acute mountain sickness affects about 25% of visitors who sleep above 8,000 feet in Colorado, according to the CDC Yellow Book, making it a real risk at several high-elevation national parks, not just a concern for mountaineers. Rocky Mountain, Yellowstone, Grand Teton, Great Basin, and Haleakalā all reach elevations where symptoms can appear within hours of arrival.

• Rocky Mountain National Park's Trail Ridge Road crests at 12,183 feet, the highest continuous paved road in the United States, according to the National Park Service.
• Great Basin National Park's Wheeler Peak reaches 13,065 feet, and Haleakalā's summit sits at 10,023 feet above sea level despite its tropical, near-sea-level surroundings.
• Yellowstone's terrain averages roughly 7,875 to 8,000 feet, and Grand Teton's average elevation is around 7,900 feet, both well above the altitude where symptoms can start.
• The CDC recommends acclimatizing 2-3 nights around 8,000-9,000 feet before going higher, and avoiding a jump from low elevation to above 9,000 feet of sleeping elevation in a single day.

Which National Parks Sit at High Elevation?

Several of the most-visited national parks reach elevations high enough to trigger altitude symptoms in otherwise healthy visitors, especially those arriving directly from sea level.

Rocky Mountain National Park's Trail Ridge Road is the standout: it climbs to 12,183 feet and is the highest continuous paved road in the country, according to the National Park Service, with 11 miles of the route above treeline. Visitors driving up from Denver, at about 5,280 feet, or Estes Park can gain more than 6,000 feet of elevation in a single afternoon.

Yellowstone and Grand Teton sit lower than Trail Ridge Road but still high overall. Yellowstone's terrain averages around 7,875 to 8,000 feet, and Grand Teton's average elevation is close to 7,900 feet, with the Grand Teton peak itself reaching 13,775 feet. Most park lodging and trailheads in both parks sit above the altitude where the CDC's acclimatization guidance applies.

Great Basin National Park in eastern Nevada is easy to underestimate: Wheeler Peak reaches 13,065 feet, and the park's popular Bristlecone and Glacier Trail hikes both start well above 9,000 feet and climb from there.

Haleakalā National Park is the least intuitive entry on this list. Despite sitting in tropical Maui, its volcanic summit rises to 10,023 feet above sea level, and visitors often drive there directly from sea-level beach resorts in under two hours, one of the fastest elevation gains available anywhere in the National Park System.

What Are the Symptoms of Altitude Sickness?

Acute mountain sickness (AMS) feels similar to a hangover: headache is the defining symptom, often along with fatigue, loss of appetite, nausea, and occasionally vomiting, according to the CDC Yellow Book. Symptoms typically start 2 to 12 hours after arriving at a higher elevation and are often worst during or after the first night.

More serious forms, high-altitude cerebral edema (HACE) and high-altitude pulmonary edema (HAPE), are rarer but dangerous. Warning signs include confusion, loss of coordination, or shortness of breath at rest, and the CDC advises immediate descent to a lower elevation if these appear, since they can become life-threatening without treatment.

How Do You Avoid Altitude Sickness?

The CDC's core guidance is straightforward, though it requires planning a trip's pacing in advance rather than reacting once symptoms start.

1. Acclimatize gradually — the CDC recommends spending 2-3 nights around 8,000-9,000 feet before going higher, rather than driving straight from sea level to a mountain summit.

2. Avoid a same-day jump above 9,000 feet of sleeping elevation when arriving from low elevation, per CDC guidance.

3. Stay hydrated and limit alcohol, since both dehydration and alcohol can worsen AMS symptoms in the first 24-48 hours at altitude.

4. Avoid heavy exertion on your first day at a new elevation — save strenuous hikes for after you've acclimatized, not the afternoon you arrive.

5. Know the descent rule: if headache, nausea, or fatigue don't improve with rest, or if you notice confusion or shortness of breath at rest, descend to a lower elevation rather than pushing through.

Travelers with heart or lung conditions, sickle cell trait, or who are pregnant should talk to a doctor before a high-altitude trip. The CDC notes that some medical conditions warrant extra precautions or preventive medication like acetazolamide at elevations these parks reach easily in a single day's drive.

Frequently Asked Questions

How high do you have to be to get altitude sickness?

Symptoms of acute mountain sickness can begin around 8,000 feet, and the CDC reports it affects roughly 25% of visitors who sleep above that elevation in Colorado. Rocky Mountain National Park's Trail Ridge Road (12,183 feet), Great Basin's Wheeler Peak (13,065 feet), and Haleakalā's summit (10,023 feet) all sit well above that threshold.

Can you get altitude sickness at Yellowstone or Grand Teton?

Yes. Yellowstone's terrain averages roughly 7,875 to 8,000 feet and Grand Teton's average elevation is close to 7,900 feet, both near or above the 8,000-foot threshold where the CDC says symptoms commonly start, especially for visitors arriving directly from sea level.

How long does it take to acclimatize to high altitude?

The CDC recommends 2 to 3 nights at 8,000-9,000 feet before going higher, since acclimatization is a gradual physiological process, not something that happens in a few hours. Visitors on short trips who can't build in that time should plan lighter activity for the first day at elevation instead.

Is Haleakalā's summit really high enough to cause altitude sickness?

Yes. Haleakalā's summit reaches 10,023 feet, well above the altitude where AMS symptoms typically begin. Because most visitors drive there directly from sea-level Maui resorts in under two hours, they skip any gradual acclimatization, which is part of why sunrise-viewing visitors sometimes report headaches or nausea at the summit.

What should I do if I get a headache at a high-elevation park?

A headache with fatigue or nausea within the first 12 hours at elevation usually points to mild acute mountain sickness. The CDC recommends resting at the same elevation, hydrating, and avoiding further ascent or alcohol; if symptoms worsen or you develop confusion or shortness of breath at rest, descend to a lower elevation and seek medical care.