A motorcyclist died of suspected heat exposure and another was hospitalized for severe heat illness on Saturday amid record-setting temperatures at Death Valley National Park in California, park officials said.

The motorcyclist who died was not identified or describe by age or gender, and the condition for the patient who was hospitalized was unavailable.

The Inyo County Coroner Office did not immediately respond to a request for information.

Four others in the same group of riders were treated at the scene for “heat stress,” National Park Service Ranger Nichole L. Andler said by email Sunday.

The park service said in a statement Sunday that the six were riding near Badwater Basin, an area of salt flats in the park that includes the lowest point in North America.

The area is south of the Furnace Creek Visitor’s Center, where the National Weather Service on Saturday recorded a high temperature of 128 degrees late in the afternoon, a reading one degree above the previous high for July 6, set in 2007.

Science was not working in the riders’ favor, the park service indicated. The temperatures were well above the 99-degree line over which ambient air provides little cooling to humans, it said.

Motorcyclists often wear thick, heavy protective gear, making cooling even more difficult. And helicopters serving as air ambulances that can more quickly traverse the Mojave Desert’s expanse are often grounded when liftoff becomes difficult in warmer air, which spreads molecules that favor wider wings or blades and herculean thrust.

“High heat like this can pose real threats to your health,” park Superintendent Mike Reynolds said in Sunday’s statement. “While this is a very exciting time to experience potential world record setting temperatures in Death Valley, we encourage visitors to choose their activities carefully.”

The park, under an “extreme summer heat” alert, advises visitors to avoid hiking after 10 a.m. and be prepared for life-threatening heat by being vigilant about clothing, shade and water intake. The park service also warns that cellphone reception is often nonexistent in Death Valley.

The National Weather Service had forecast record-breaking heat for Death Valley, nearly through midweek, as it roasts under a high pressure dome that’s heating up much of the west.