ApproachStart from the Carson Pass parking lot. During winter months, you can most likely head straight up the hill in front of you, following your map/compass towards the obvious peak where one would think Red Lake Peak should be. Once the snow melts, this hill is choked with brush, and a better route may be to follow the ridgeline directly from the pass so as to avoid this.
The peak itself is not completely visible from the pass; a false summit blocks the view, although if you squint enough, the summit crags are just visible behind this false summit.
Route DescriptionOnce you reach the false summit seen from Carson Pass, the final destination is obvious, although the route-finding to make it up there is less so. An inviting crag (itself a fun scramble) stands between you and the summit; the rocky mass behind this marks the actual highpoint.
Traverse to the south/east around the first couple of crags; during winter months, a well-worn ski trail generally leads along here. Towards the northern end of the summit blocks, there is reportedly a gully that leads up towards the summit, but I didn't locate this when I was up here. It may be simpler to just head directly up to the summit without searching too much for this, as there are a number of possible routes up to the top, all with solid rock and excellent holds, but varying degrees of exposure.
The easiest route is probably to head towards the northeastern end of the summit blocks, where you'll find a short wall leading to a notch; climb this, and downclimb from the notch to reach a 20- or 30-foot ledge. Walk south along here, and climb up to reach the summit. A more direct (and enjoyable) alternative is to climb a rocky wall south of the summit, reaching a short knife-edge ridge that leads a few yards north to the summit.
Pete Yamagata's Northern Sierra Peaks Guide offers an extremely detailed description of a route, which sounds similar to the easier route described above.