ON the northern border of a vast desert preserve, halfway up a dusty hillside and overlooking a great forest of Joshua trees, David Nichols knelt to brush off a flat gray stone.
"Yep, this is one right here," he said, motioning toward a sheet of exposed bedrock. A group of small, closely spaced stones, like tiny turrets in the sand, formed a vague ring at his feet. "These supposedly kept the rodents out."
Mr. Nichols, one of two full-time research archaeologists employed at Mojave National Preserve, was showing off a recent discovery. On a nondescript hill, a quarter-mile off a four-wheel-drive dirt track, the remnants of a prehistoric way of life lay scattered in the sand.
Throughout Mojave National Preserve, a 1.6 million-acre park about 140 miles northeast of Los Angeles, the subtle traces of a bygone civilization are all around. Pictographs painted on cave walls, dart tips in the sand, shelters, fire rings and pottery shards are common in the area, where generations of prehistoric people lived and died. Indeed, Mojave National Preserve is an amateur archaeologist's dream, with undocumented sites open year-round for visitors to explore in the empty, undeveloped park.
The Drying Pallet Site, as Mr. Nichols has come to call his new hillside finding, features 21 limestone slabs encircled with rocks that were carefully placed hundreds of years ago. The indigenous people, Mr. Nichols told his small tour group, used the sunny protected rock platforms to prepare Joshua tree blossoms.
"It was dried like beef jerky," he said of the white blossoms, which each spring still daub the land below in one of the world's largest and densest forests of Joshua trees. "Food in the desert was dried for preservation; it was the only way."