At sea level, the air contains nearly twenty-one percent oxygen; the air at the summit of Denali contains less than half of that, and it’s categorized as Extreme High Altitude. (The 26,000-foot-plus [7,900-meter] peaks of the Himalaya are considered Ultra High). High Camp, sitting at just over 17,000 feet (5,200 m), would at least get Grace down to the next level of Very High Altitude, and every thousand feet they descended would give her more oxygen with which to recover.
