Paul Miller, 51, went on a hike alone. He called his wife Friday morning from the 49 Palms Oasis trail, and that was the last time anyone had heard from him.
Park rangers eventually found Miller's vehicle at the 49 Palms Oasis trailhead, but even with 90 rescuers involved in the search, there's still no sign of him.
"Still no sign, not even so much as a footprint, so it's somewhat of a mystery," said park spokesperson George Land.
Summertime temperatures can surpass 100 degrees in the park.
The San Bernardino County Sheriff's Office is leading the search and getting help from other agencies.
KESQ-TV reports Miller's hometown is Guelph, Ontario.
The Associated Press contributed to this report.