Red Slate Mountain is the second highest peak in the Mammoth Lakes area of the Sierra Nevada after Mt. Ritter, but is climbed far less often. It is one of the 33 Mountaineers Peaks in the range, and has the additional distinction that there is no higher peak along the Sierra Crest north of it. The views from the summit are outstanding, taking in panoramas as far north as Mt. Dana in Yosemite, Mt. Ritter and the surrounding peaks in the Minaret area to the northwest, the Silver Divide to the southwest, the Mono Recesses to the south, and the Mt. Abbot group and beyond to the southeast. Impressive as that all might sound, the peak is a huge pile of rubble, and quite the slog from either the east or the west. Red Slate is one of the designated Mountaineers Peaks because it does have one outstanding climbing route - the North Couloir offers 1,000ft of 40 degree snow/ice climbing.
The peak is usually climbed as a multiday trip from one of the trailheads, or as a side trip from the John Muir Trail. The peak can also be climbed as a long dayhike, with 5000ft of climbing and 22 miles roundtrip.
The easiest access is from the McGee Creek trailhead off US395. The turnoff is well marked on the highway, located between the Convict Lake exit to the north and the Hilton Creek exit to the south. The pavement ends about a mile from the trailhead, and turns to packed gravel. Drive past the pack station and park at the end of the road. There are some key parking spaces under trees that provide at least partial protection for your vehicle from the oppressive sun in this mostly treeless canyon.
Convict Lake to the northwest of McGee Creek can also be used to access Red Slate Mtn, but the approach is longer with 500ft of additional elevation gain. Convict Lake can be reached from US395 via the Convict Lake Rd, just south of the Mammoth airport. Convict Lake is a popular recreation lake, primarily for fishing. There is a "resort" there, complete with a restaurant, general store, and bountiful camping.
There are no fees for overnight parking at the McGee Creek or Convict Lake trailheads, and a Wilderness permit is only needed if staying overnight in the John Muir Wilderness that surrounds Red Slate Mtn.
Everything you need to know about conditions, permits and regulations can be found on the Eastern Sierra - Logisitcal Center page.
Climbing can be done any time of year, but usually in June-Oct when the peak is mostly free of snow. In early season the approach to McGee Pass will have much snow, and even in mid-summer climbers should expect snow on the northeast side of the pass.
Camping is allowed most places in the John Muir Wilderness. The lower parts of McGee and Convict canyons are very dry and usually quite hot in the summer. They make terrible places to camp. The upper reaches of these canyons in contrast are superb; cooler, large trees, and scenic lakes.
"Named by the Whitney Survey in 1864 [and climbed by James T. Gardiner]. This mountain and several others of similar coloring were called 'Red Slate Peaks.' The present name is on Hoffmann's map of 1873, but it is not clear whether it applies to this peak or to Red and White Mountain."
- Peter Browning, Place Names of the Sierra Nevada