Updated

A dig for clandestine graves at Charles Manson's last hideout was called to an end Wednesday after yielding no bodies and leaving scientists puzzled over the clues that had enticed them to come this far.

The dig had been scheduled to last three days, ending Thursday. But the work went faster than scheduled, with the crew of 20 digging until dusk, then camping out at night beside the ranch house Manson and his followers had used.

"So far there have been no human remains found," Inyo County Sheriff Bill Lutze said after the four sites with the greatest probability of holding human remains were dug up. "We're finishing up this site and that'll be it for the day — nothing."

Manson and his followers hid out at the ranch following their killing spree in Los Angeles. For years, rumors have swirled about other possible Manson victims, including hitchhikers and runaways who visited the site and were never heard from again.

Scientists who conducted a preliminary probe of the rugged, remote site in February said they identified several spots that could be graves, leading Lutze to conduct the exploratory excavation.

By Wednesday afternoon, the four most promising sites had been excavated and the dirt sifted. They revealed little more than a pack rat's nest, animal bones, ash, and some stones used to make arrowheads.

The scientists and law enforcers involved said the unusual physical environment made it harder to determine what was underground. Plants that exude unusual chemicals and rocks with magnetic properties were throwing off their equipment, they said.

"I haven't been this frustrated in a very long time," said Arpad Vass, a senior researcher at the Oak Ridge National Laboratory.

A closer look at the first site on Tuesday turned up only a .38-caliber shell casing. Law enforcers quickly determined it was recent. No human remains were found there, sheriff's officials said.

Investigators then found what appeared to be ash and small animal bones at the second site, which will be turned over to the National Park Service for an archaeological dig.

Vass said the excavation is a learning process.

"We're trying to improve the science. It's in its infancy," he said. "Every exercise we do like this will further the science so that one day we can say, 'Yes there is a body here."'

Manson's clan was ultimately prosecuted for nine murders that took place in the summer of 1969. He is serving a life sentence at Corcoran State Prison.