Had they not gotten off track, a pair of hikers on Mount Williamson, California’s second-highest peak, would have missed it.

In a remote area about three hours from the mountain’s summit, a bleached skull peeked out from beneath gray boulders.

“We were in disbelief,” said one of the hikers, Brandon Follin, 22, who was with his friend, Tyler Hofer, 33. “My first thought was maybe it was a prop or something like you see in a science class.”

As they got closer, they spotted hints of other bones amid the boulders. Clearing away the rocks revealed a skeleton, which was almost fully intact, with a pair of disintegrating leather shoes and the remnants of a belt.

Investigators at the Inyo County Sheriff’s Office are trying to identify the hiker and solve the mystery of why he or she never got beyond this spot in “the bowl” as that stretch leading up to the top of Mount Williamson is known.

The mountain is in the Sierra Nevada, more than a four-hour drive from Los Angeles or Las Vegas. The primary rule of getting to the top is not to drop anything while navigating the bowl, said Tinh Le Trung, who works at Elevation, Sierra Adventure Essentials and did the hike two years ago.

“Imagine a bunch of sharp boulders that you have to hop between,” he said. “Lose your phone and you can’t get it back.” And if you twist your ankle on one of the unstable rocks, “you’re done,” he said.

That is particularly true if you have come up one of the more remote sides of the bowl: “No one will find you,” Mr. Trung added.

People from across the country come for the hike. For Mr. Follin and Mr. Hofer, who are both from San Diego, the attraction was “to do another fourteener,” Mr. Follin, said, using the lingo for a 14,000-foot peak.

Mr. Hofer saw the chalk-white skull first. They were about 12 miles into their hike from the spot where they camped the night before. They started crossing the bowl and took the wrong route around a lake.

“I looked down and saw something strange underneath a small boulder,” Mr. Hofer wrote in a Facebook post. “I thought it looked like a bone of some kind, and after closer inspection, it was indeed a human skull.”

The hikers were at a loss about what to do.

Mr. Follin said not touching the bones and calling the authorities seemed wise, but they were far beyond cell service. They opted to document their findings, moving only the foot for a better photo of the shoe.

After they reached the summit, they called 911. On Wednesday, the remains were removed by California Highway Patrol helicopter.

The Inyo County Sheriff’s Office said it could not yet say how long the person had been on the mountain. The sex of the person was pending a review by the county coroner’s office.

Forensic anthropologist Alison Galloway, a professor emerita of anthropology at University of California Santa Cruz, said the length of time it would take for a body to become a skeleton depends primarily on the temperature and local insect population.

In a warm area with certain types of flies, it could happen in six months. “The colder it is, the longer it will take,” she said.

Dr. Galloway had not seen the skeleton but said investigators typically hope there is still some soft tissue because then they “can get within a few months.” But with only bones, it is trickier to determine whether someone has been there for one year or 20.

In this case, the shoes and belt may offer more useful clues than the skeleton itself, she said. There are a variety of other techniques to determine timing. She pointed to Carbon-14 testing, for example, which can reveal whether someone died before the 1950s.

Strangely, the use of atomic bombs in the 1950s and 1960s released enough changes in the carbon ions in the atmosphere to be reflected in the bones of people who were born after that time, she said.

Carma Roper, a spokeswoman for the sheriff’s office, said investigators had reviewed lists of everyone reported missing in the area in the last couple of decades. That included Lt. Matthew Kraft, a Marine from Connecticut who vanished during a ski trek through the Sierra in February, and Matthew Greene, a climber from Pennsylvania last seen in the Mammoth Lakes area in 2013.

Based on the skeleton’s location, nothing has matched up.

There is “no evidence to suggest foul play at the scene,” Ms. Roper, who declined to elaborate, said. Mr. Follin, who said he had no forensic background, was skeptical.

“The way the body was laid out, it was lounging” as if someone buried the hiker after he or she died, he said.

Mr. Follin and Mr. Hofer said they spotted a big dent in the skull, as if it were fractured. Ms. Roper said that was inaccurate.

The sheriff’s office is attempting to obtain a DNA sample from the remains. Dr. Ed Green, a professor at University of California Santa Cruz, who is not involved in the investigation but specializes in extracting DNA from old remains, said that if no hair was available, an ear bone or tooth were generally reliable sources of DNA.

Investigators can then see if the DNA matches anyone in a missing person’s database. If not, and no promising leads emerge, Ms. Roper said the sheriff’s office planned to use forensic genealogy, a technique that relies on using cousins in genealogy databases to identify a person.

“If someone knows someone who hiked in the area and disappeared, they should contact us,” she said.