There are some sources of information about the Granite Chief Wilderness online, but they are all missing something, so I’ll do my part to contribute those missing parts. Though I’ve spent a lot of time in the wilderness over the last four years, much of it has been on the PCT, and I’ve not (yet!) even seen all the trails.
The Granite Chief Wilderness was established in 1984 as part of the California Wilderness Act. It is about 25,000 acres, and almost entirely in the headwaters watershed of the Middle Fork of the American River (and the Rubicon River, which flows into the Middle Fork).