Thunder Mountain is the northernmost of what Southern California peak baggers refer to as the “Three T’s”, the other two being Telegraph Peak (8,985) and Timber Mountain (8,303). Thunder Mountain is by far the easiest of the three, due to the existence of a road (closed to vehicle traffic) to the summit, and a trailhead 1,000’ higher than the typical approach for the other two. The peak sports a modest ski area (Mt. Baldy), which operates a lift to Baldy Notch. The truly lazy can shell out the $10 ($15 round trip, kids $8) for a ride up to the Notch, have lunch at the restaurant there, and take a leisurely stroll of about 3 miles round trip and 800 feet vertical gain.
From time to time on various message boards I find people asking "I'm in Los Angeles for a few days. Are there any hikes I can do?" Thunder Mountain is one of several possible answers to that question, providing everything from a strenuous 12-mile traverse of the 3-T's to a kid-friendly stroll from the restaurant at Baldy Notch.
After a good snow you can cross country ski from Manker flat all the way up the road and back. Given the steep nature of the San Gabriel mountains, there aren't too many other places in the range that offer that kind of skiing. Of course, you have to hit the conditions right after a storm, otherwise you'll be skiing rocks.
From either the 210 Freeway or the 10 Freeway take the Mountain Ave. (Mount Baldy) exit and head north towards the mountains. Mountain Avenue will turn into Mt. Baldy Road. and eventually dead end at the ski area parking lot. The Ice House Canyon Resort (el. 5,000’) is an alternate point of departure. Parking is off Mt. Baldy Road on the right (heading uphill) just before heading up steep switchbacks to Manker Flat and the ski area.
Given the steep, loose nature of the terrain, ascending the peak via trail is the only sensible option. There are two main choices, as described below.
From Manker Flat. Class 1. 5 miles one way, 2,500’ gain. Park near the lower end of the ski area parking lot (be sure to display you Adventure Pass! See “Red Tape” below). Locate a gated road on the north side of Mt. Baldy Road and start walking. You’ll reach Baldy Notch after 1,500 feet gain and 3.5 miles. Pick up the fire road to the summit about 150 yards east of the Baldy Notch Restaurant. Another 1.5 miles and 800 feet gain will put you on the summit. The first 3.5 miles can be eliminated by taking the ski lift (open weekends and holidays year-round). See Trip #95 in Trails of the Angeles: 100 Hikes in the San Gabriels.
From Ice House Canyon. Class 1. 7 miles one way. 4,500’ gain. This route departs from Ice House Canyon Resort, which is about 1.5 miles above Baldy Village. The trail starts just to the right of the resort. After about 1.5 miles you reach a junction. Both lead to Ice House Saddle, 4 miles from the start. From the saddle take the trail leading left (North) up the south ridge of Timber Mountain. Follow this trail about 3 more miles past two unnamed peaks and Telegraph Peak to Thunder Mountain. The trail stays a few hundred feet below the summits, but what the heck, what’s another few hundred feet on top of 4,500? Might as well bag the other two peaks on the way…
The two routes described above can be linked in either direction, though a car shuttle will be needed. End-to-end, it’s about 12 miles. Easily doable in a day for a strong hiker. Bring plenty of water—there’s only one spring along the way, and I won’t vouch for its reliability.
See Trip #95 & 96 in John Robinson’s Trails of the Angeles: 100 Hikes in the San Gabriels. Other combinations of trail link-ups are possible. Robinson’s book is the authoritative source.
Thunder Mountain lies in the Cucamonga Wilderness within Angeles National Forest. A National Forest Adventure Pass is required to park in the ANF. Annual passes are $30, and day passes are $5. Passes can be purchased an Forest Service offices and virtually any sporting goods store in Southern California.
I’ve never camped overnight here, and it’s not clear whether wilderness permits are required or not. More to the point, there are very few spots with both water and sufficient flat ground to make camp. Most recreational users are day hikers, but some trails are long enough (and have water en route) to allow for overnight stays.
Angeles National Forest
701 North Santa Anita Ave.
Arcadia, CA 91006
Just about any time. This can be a hot, dry hike in the summer, but it’s not out of the question. In many years, there is very little snow fall and the peak can be an easy, cool walk on dry ground in the winter.
Most people do day hikes in the area. Car camping is available at the Forest Service’s Manker Flat Campground for $12/night ($10/night if you hold an annual adventure pass. The Manker Flat campground closes in the winter months.
The Forest Service office provide current conditions (See Red Tape above). Quite frankly, I've found the weather.com is just as good.