A human skull spotted by a kayaker in a cove under Battery Spencer in the Marin Headlands led authorities to skeletal remains so decomposed authorities are not certain whether they belonged to a man or a woman.

Crews rappelled 600 feet on Tuesday to recover the intact skull along with additional bones, some clothing and jewelry, said National Park Service Ranger George Durgerian.

“It was about 25 feet above the water line between Kirby Cove and the Golden Gate Bridge,” he said.

A second expedition was planned Friday for the rest of the body, and to search for other possible evidence of when and how it got there. Durgerian said it’s unclear how long ago the person died.