Grand Canyon, Arizona

Why is one of our favorites considered one of the most dangerous national parks in the US?

With jaw-droppingly steep canyon walls that drop over a mile to the churning Colorado River beneath, it would be easy to assume that falling is the number one cause of death in this historic national park.

And even though falls accounted for 27 deaths at the Grand Canyon over the past 10 years, medical issues and natural deaths nearly doubled that number, at 42, due to the scorching summer heat deep within the canyon, potentially causing or aggravating health issues.

The National Park Service warns that temperatures on the South Rim are typically 20 degrees cooler than those near the river at Phantom Ranch, which has experienced a record high of 120 degrees. This means that the heat will increase as visitors trek down.

The park service advises visitors to plan their trip during spring or late fall to enjoy fewer crowds and cooler temps. But if you visit during summer, consider a shorter day hike to avoid the heat.

And if you plan on heading to the bottom of the canyon, be sure to get an early start to avoid going uphill during the hottest part of the day.