The incident occurred at the Ka'apahu section of the park where Pi'ilani Highway meets Hana Highway. It is one of the most remote areas of Hawai'i, with cliffs towering over a narrow road that sits above a sheer drop to the sea.

The on-duty ranger, who was driving toward Kipahulu, stopped to remove rocks from the road when a boulder, estimated to be 2 feet in diameter, dropped from the cliff face sometime before 10 a.m.

Maui Fire Capt. Paul Mallo of the Hana Fire Station said he thinks the free-falling rock never made a sound as it plunged to the ground.

"There were a couple of witnesses who yelled at the ranger as it was breaking loose, but it happened too quickly for her to react," Mallo said.

According to Mallo, witnesses said that when the boulder hit the ground, it shattered into a half-dozen pieces and left a small crater.

Police received a call at 9:55 a.m., and paramedics and fire crews arrived at the scene by 10:39 a.m. There were injuries to the ranger's head and torso, and paramedics administered medication, tried electrocardiogram shocks and performed CPR, but there weren't vital signs, Mallo said.

The ranger was moved by ambulance to the Hana Medical Center, where she was pronounced dead.

She was said to be a seasonal worker from the Mainland who had been working for the park only a couple of months.

"We're in shock. We're depressed," park Superintendent Don Reeser said.

The National Weather Service reported that 'Ohe'o Gulch in the Kipahulu District received 1.3 inches of rain Monday night, which might explain the rockfall that the ranger was trying to clear. Still, it's not uncommon for individual rocks to fall in that section of the county-maintained state road, officials said.

Brian Hashiro, administrator of the county Highways Division, said that two years ago, a woman reported she was moving rocks off that section of 15-foot-wide road when her car was smashed by a boulder. Years earlier, a county truck was hit by a rock there, Hashiro said.

Area resident Lisa Hamilton said: "It's one of these tragic accidents that we've all known would happen here. Rocks are always on the road. It's a game of Russian roulette that we play when we drive around here."

Hamilton recalled one rainy night when she was driving in the same area and her car was trapped by rocks that fell in front of her and behind. She spent the night crouched in a ball on the floor of her vehicle.

"I was terrified," she said.

Hashiro said it's best to call a road crew rather than remove any rocks yourself.

"If a rock falls there, there's a good chance another rock will come down in the same area," he said.