The National Park Service has an official website about Yosemite National Park wilderness at
http://www.nps.gov/yose/planyourvisit/y ... erness.htm
It has information on how to request a Wilderness Permit (required for overnight travel in Yosemite backcountry), bears, trip planning, and current conditions.
More general information on backpacking is at
http://www.nps.gov/yose/planyourvisit/backpacking.htm