National Park rangers say they received a report of two missing people and multiple others injured after flash flooding hit Tatahatso Camp near River Mile 38 on the Colorado River.
Grand Canyon Search and Rescue dispatched two paramedics to the scene to assess and treat patients.
Monsoonal weather in the area limited access to the scene for the overnight search and rescue operations.
At around 2:30 a.m. on Thursday, park rangers say one of the patients, who was in critical condition, was flown out via the Arizona Department of Public Safety helicopter. Four more patients were evacuated by air on Thursday to a nearby medical center. Rangers say they are in stable condition.
Around 11 a.m. on Thursday, the Grand Canyon Regional Communications Center received a report from a commercial river trip that found the two missing people near Tatahatso Camp. One of those individuals was uninjured while the other was dead.
The woman found dead has been identified as 29-year-old Rebecca Copeland of Ann Arbor, Michigan.
Flash floods are common in the desert southwest, including Northern Arizona and Grand Canyon National Park. This is due to the arid, sparsely vegetated environments found in these areas that have little capacity to absorb rainfall.
Rain runoff moves rapidly through the narrow canyons and steep terrain found throughout the region.
In many areas, even small storms can turn normally dry streambeds into raging torrents of water in a matter of minutes, according to rangers.
An investigation is now underway by the National Park Service in coordination with the Coconino County Medical Examiner. No additional details are available at this time.