Woman dies hiking in Grand Canyon amid triple-digit temperatures: National Park Service

A woman was pronounced dead early Monday morning after becoming unconscious during a hike in the Grand Canyon as temperatures reached triple digits, officials said.

On Sunday at approximately 6:30 p.m., a U.S. park ranger received a report about a hiker who was in distress in the Tuweep area of Arizona's Grand Canyon National Park, the National Park Service (NPS) said in a news release.

Officials said a 57-year-old woman was on an 8-mile hike in the remote area of the park when she lost consciousness. "A ranger arrived on scene at approximately 1 a.m. on July 3 and pronounced the hiker deceased," the NPS said.

The temperature at Tuweep was over 100 degrees on Sunday, NPS said. At Phantom Ranch, southeast of the site and near the Colorado River, it reached 114 degrees.

Parts of the Grand Canyon are under an excessive heat warning through Wednesday, NPS officials said. Park rangers recently told hikers and backpackers to prepare for extremely high temperatures in the weeks ahead.

About 35 million Americans are on alert for dangerously high temperatures heading into the Fourth of July, with the center of the heat dome over the West.

On Monday, temperatures reached 114 degrees in Phoenix, 112 in Las Vegas, 114 in Palm Springs and 120 in Death Valley.

In at least eight southern states from Texas to Georgia, Saturday's heat index ranged from 105 to 115 degrees.

The excessive heat which parts of the country have been experiencing in recent weeks has been linked to multiple deaths.

Last month at least 13 people in Texas died from heat-related illness, according to The Associated Press.

Emergency room visits in Texas have increased from the same time last year, as the state experiences extreme heat, according to the Centers for Disease Control and Prevention.

As for the Grand Canyon, park rangers have advised people to avoid hiking the inner canyon between 10 a.m. and 4 p.m.

"Hiking in extreme heat can lead to serious health risks including heat exhaustion, heat stroke, hyponatremia, and death," the National Park Service said.

The NPS and the Mohave County Medical Examiner are investigating the incident.

ABC News' Emily Shapiro, Julia Jacobo, Nadine El-Bawab, Kenton Gewecke and Max Golembo contributed to this report.