The name Trinity Mountains refers to a rugged North/South ridge line that runs from Dog Mountain (just above Anderson Ranch Reservoir) to Sheep Mountain (just north of the Middle Fork Boise River). The name was used by miners but has not been officially adopted by the government. Trinity Mountain (9,451 feet) is the highest point on the ridge. Other notable summits include Peak 9165, Peak 9140, Fiddlers Perch, Peak 9037 and Peak 8554.
Much of the Trinity Mountain area was burned by a forest fire in 2012. Still, there are living trees to be found and the many high mountain lakes around Trinity Mountain provide good camping.
Featherville, Idaho Access. At the south end of Featherville, turn onto FSR-172 which is signed for Trinity Lakes. Follow FSR-172 for 15 miles to its junction with FSR-129, Trinity Ridge Road. FSR-129 is the Trinity Ridge Road. Turning left/south will lead you to the various Trinity Lakes and then to the pass between Trinity Mountain and Peak 9037 in 5.0 miles. FSR-129 then descends down to Anderson Ranch Reservoir. Turning right/north will take you first to Scotch Benchmark and eventually to the base of Steel Mountain. These road do get regular maintenance and I have spotted passengers cars on them. Nevertheless, the quality and steepness vary and they can be quite rough in places. A high clearance vehicle with AT tires is recommended. The road above the lakes requires a 4WD.
Southern Access. FSR-129, Trinity Ridge Road [(E)(2.2) Page 155] leads up from Anderson Ranch Reservoir to the pass between Trinity Mountain and Peak 9037. It is a rough road that is often in need of major repairs. A 4WD is required.