Rain Peak is on the Payette National Forest just north of McCall, Idaho. It is found in the Lick Creek subrange of the Salmon River mountains. Rain Peak is a classic Lick Creek range peak, which means it is granite and has a somewhat gentle southern slopes but a precipitous north face.
Rain Peak is within the 56,000 acres that burned in the 1994 Blackwell fire, so there is little old-growth. However, the area is re-generating quickly with lots of undergrowth and bushes. Because the Payette N.F. chooses not to spend much money on non-motorized recreation, the regeneration in the burn can make trails hard to find and follow. With trails hard to follow, and no trails leading to the actual peak, good map and compass skills are important. Even so, navigation is not terribly difficult because with no trees to obstruct your view, it's almost always easy to find a landmark.
The McCall area gets lots of winter snow (and the mountains even more so), so the roads to access this peak are closed from roughly late November until early to mid-June. Also, this is a popular big-game hunting area. Check before you head out.
There are three main ways to approach Rain Peak. In any case, a good topo and/or a Payette National Forest map should be part of your equipment.
This route is described on page 113 of the excellent guidebook, Idaho, A Climbing Guide. First, get to McCall. Either take Highway 55 north for about 100 miles from Boise, or come south from Riggins and New Meadows. From downtown McCall, take the Lick Creek road, also signed as the turn for Ponderosa State Park. Turn right after the golf course, then take another right off the pavement (signed) in about three miles. Follow the Lick Creek road for about 23 miles to Lick Creek Summit, then drop down the other side about 1/2 mile to the Duck Lake trailhead. The road can be rough, but it's generally passable for any vehicle. Park at the trailhead.
Follow the Route 1 instructions for McCall, then head clockwise around Payette Lake to Warren Wagon Road, which continues around the lake. At the north end of the lake, stay on the pavement, heading for Upper Payette Lake. As you near the upper lake, look for the Pearl Lake road (marked) on the right. High clearance recommended.
Follow the Route 1 instructions to McCall and then to Lick Creek Summit. At the summit, park. There is room for several vehicles to pull off the road.
No red tape.
There are many campgrounds from which to choose, depending on which route you intend to follow.
For Route 1 and Route 3, the closest official campground that is worth anything is the Lake Fork Creek campground, about 10 miles before Lick Creek Summit. The campground is quite nice (although primitive), but also quite popular. Normal Forest Service fees etc. apply.
The map shows a Black Lee campground, but it's mostly just a dirt pull-out, and not recommended.
However, there are numerous unofficial campsites along Lake Fork Creek.
For Route 2, Upper Payette Lake has very nice lake-side camping. However, it is a popular spot so may require reservations.
For something more civilized, you can stay in McCall at either one of the many hotels, or try Ponderosa State Park (usually requires reservations).
Last, the area surrounding Rain Peak lends itself to backpacking. Generally, you won't see many people. The fishing tends to be good to fantastic.
From the Duck Lake trailhead, walk the easy trail to Duck Lake. This trail is well-maintained and quite popular as a day hike. It is about 1 miles with around 450' of gain. At the outlet, leave the trail and find a way to cross the wetland and creek, heading west. Turn northwest and head for the saddle on the south ridge of Rain Peak. This is about 1.75 miles and 1300' of gain. From the saddle, it's another 400' but less than 1/2 mile. Class 1 to Duck, then Class 2 and some Class 3 approaching the ridge and near the summit.
From the Pearl Lake trailhead, follow the trail to Pearl Lake. Then head east and northeast, avoiding the wetlands, to gain the saddle to Marge Lake. You can immediately jump on the NE ridge of Rain, or go down to the lake first. In either case, gain the ridge and follow it to the summit. Class 1 to Pearl, then Class 2, with a bit of Class 3 high on the ridge near the summit. 5 miles each way, with a total of about 3000' of climbing (only 1600' of actual gain).
From the summit area, it is all bushwacking. Find your happy place and follow your map and compass. In a NW direction, hike to Burnside Lake in about 1.75 miles and 900' of gain. Continue through the saddle above Burnside, then swing a bit more northerly heading for the south ridge of Rain Peak. The summit is about 1.5 miles and 1100' of gain. Mostly Class 2 and a little Class 3 approaching the ridge and near the summit.
Payette national Forest
City of McCall
Splattski trip report
Brundage Mountain web cams (including McCall)
Idaho road conditions
For additional information on this climb and other peaks in the area, please see Tom Lopez's excellent book, Idaho: A Climbing Guide