Plummer Peak lies in the heart of Idaho's Sawtooth Wilderness, part of the Sawtooth National Recreation Area within the Boise National Forest. It is a wild peak that takes considerable effort just to get to, so it does nto get climbed often, even though it is only Class 3. Because it's main route shares a lake basin with Everly Peak, the ideal trip would include both peaks.
There are a number of trails that lead to the area leading to a climb of Plummer Peak. For most, the best route would include hiking the trail to Everly Lake and Plummer Lake. This trail starts in Benedict Creek, which can be reached by hiking up the South Fork of the Payette River from Grandjean.
Alternately, one can hike down the trail from Ingeborg Lake and the Ten Lakes Basin. The easiest access to Ten Lakes Basin is probably up Redfish Creek from Redfish Lake, but some prefer to hike over the divide from Toxaway Lake and the Tin Cup trailhead on Pettit Lake. Your author got to Ingeborg Lake from the Alpine Creek drainage and across Flytrip basin. See the links section for a trip report.
The standard route listed in Idaho, A Climbing Guide
is to climb the west ridge from Plummer Lake. This is a straightforward route climbing talus and boulders up the ridge to just south of the actual summit, then an easy hike north to the summit (see the main picture of this page).
An alternate route climbs up above Three Island Lake. From there one can climb the east face to the east ridge, or perhaps slug your way up some really steep talus to the saddle of the east ridge. Either way, gain the upper portion of the east ridge for easy scrambling and hiking for the last 300' to the top.
For either route, from the base of the peak the route is roughly 3/4 mile of Class 2 and Class 3 with about 800-1000' gain.
Sawtooth Wilderness permit required (self-issue on the trail).
Note that special restrictions on fire apply to most areas of the Sawtooth Wilderness. Stoves are preferred, but fires are acceptable in some areas only
with a fire pan or blanket.
This is pristine country, so please respect that: pack out what you pack in, leave no trace, camp away from water, etc.
There are excellent campsites around Everly Lake, Plummer Lake, and Three Island Lake. There are other campsites farther away, but still within easy access of the peak. It is unlikely that you will have any company at these, so take your pick.
Sawtooth National Forest
Smiley Creek web cam (choose View 2)
Stanley cam and current weather
Sawtooth national Forest Avalanche Center
For additional information on this climb and other peaks in the area, please see Tom Lopez's excellent book, Idaho: A Climbing Guide.