The Yuba County Five: Five men, four of them mentally-disabled, and one of them mentally-disturbed, went missing on the night of February 24th, 1978, after attending a college basketball game. Several days later, their car was found abandoned in a remote part of the Plumas National Forest, far out of the way from the location the men had been beforehand. Investigators to this day can't find an explanation for why the car was abandoned as it could've easily been pushed from the snowdrifts and was in good working order, or how it ended up in such a remote area in the first place.
Months later, in June 1978, one of the five men's' bodies was found in a trailer nineteen miles away from the car. It was the body of Theodore "Ted" Weiher, it appeared that he survived for as long as three months after the men were last seen.
The most bizarre thing is that all the supplies in the trailer such as food, water, and heating materials were completely untouched, meaning that Weiher had intentionally starved, and frozen himself to death for seemingly no reason. His body was also find wrapped in eight sheets, including around his head. His frostbitten feet were nearly gangrenous, and his shoes were missing.
The bodies of Jack Madruga and Bill Sterling were found eleven miles from the car on opposite sides of the road. The bodies had been partially devoured and scattered by scavengers and autopsies showed that both had died of hypothermia. Two days later, the backbone belonging to Jack Huett was found by his father just two miles north of the trailer Weiher was found in, and his skull was later found downhill just 300ft away.
The only trace of the last member of the group, Gary Mathias, were his shoes that were found not too far out in the nearby woods by the trailer. Forest service blankets and a rusted flashlight were found in an area northwest of the trailer, but it could not be confirmed how long they'd been there, or if any of the group including Mathias used them.
A key thing to mention is Gary Mathias suffered from diagnosed Paranoid Schizophrenia and had frequent psychotic episodes. His body is the only one still not accounted for, and over forty years later, no one has been able to find him, nor figure out what happened to the men that fateful snowy night.
Edit: Added and corrected some details and major mistakes. Sorry!