What is Altitude Sickness or Acute Mountain Sickness (AMS)?

It is Caused By A Decrease In Oxygen Levels at High Altitudes in Colorado

Chart below shows the amount of oxygen at altitude – note how it decreases as you go up in altitude:

Oxygen at Sea Level: 0 Feet
Oxygen in Denver, CO: 5,280 feet Above Sea Level
Oxygen in the town of Aspen: 7,945 feet above Sea Level
Oxygen at the base of Steamboat: 8,020 feet above Sea Level
Oxygen at the base of Vail Resort: 8,120 feet above Sea Level
Oxygen at the base of Crested Butte Mountain Resort: 9,380 feet above Sea Level
Oxygen in the town of Breckenridge: 9,600 feet above Sea Level
Oxygen at the Summit of Steamboat: 10,568 feet Above Sea Level
Oxygen at the Summit of Aspen Mountain: 11,212 feet above Sea Level
Oxygen at the Summit of Vail: 11,570 feet Above Sea Level
Oxygen at the Summit of Crested Butte Mountain Resort: 12,162 feet Above Sea Level
Oxygen at the Summit of Breckenridge: 12,998 feet above Sea Level.
Oxygen at the Summit of Telluride: 13,150 feet above Sea Level