See getting there on the main page
Total Round trip distance 14.0± miles, 6,850’ feet of elevation gain.
6.7 miles to South Thunder, 6,400’ of elevation gain
1.0 mile to North Thunder from South Thunder, 450’ of elevation loss and then gain along the ridgeline.
Start at the Trailhead parking lot, the stairs lead off from the north end of the lot. The first 0.5 mile consists of hiking within a residential area while fenced in like cattle but soon you will arrive at Lower Bells Canyon Reservoir at about another 0.25 of a mile. Continue around the west and north sides while starting to head east. The trail continues on a gentle grade across a wooden bridge (0.5 miles) and soon starts to gain grade. The trail follows the stream on the south and then crosses over to the north for the next 2.25 miles, while traveling the last 2.25 miles a few waterfalls are present but are well hidden.
The trail opens up into a meadow while starting to head southerly, good camping can be found here. Continue south while heading up a steep grade. The trail, which has been obliterated from windblown down trees, follows a stream that will be on your right. The trail is hard to follow, try to stay always to all drainages that want to lead to your left. If you miss the correct drainage (the one to Upper Bells Reservoir) don’t worry the others will open up eventually and South Thunder will come into view. So after 5.1 miles from the trailhead you will come across Upper Bells Reservoir. From here I wasn’t able to find a consistent trail, so contour around to the saddle southwest of South Thunder, gain elevation to the saddle and start heading directly north to the summit.
From the summit of South Thunder head along the ridgeline for 0.2 mile to the junction of another ridgeline, from here you are looking down into Thunder Mountain Bowl. Start down climbing to a point where you feel comfortable to contour for 0.2 mile (east) and regain the ridge. Shear drop offs required the downclimb from the ridge. The ridgeline is where the class 3 and 4 scrambles come into play (see photos of the ridgeline).
After gaining the ridgeline continue north for another 0.6 mile to North Thunder.
From here either back track (a much long route) or continue along the ridge from North Thunder for 0.3 mile or when you feel comfortable to start down climbing. What ever your preference is try to hit the drainage and follow it back down to the meadow as referenced on the ascent.
This route is not an easy hike up and down, there is no real trail or path from upper bells reservoir to the summits and back. You’re exposed for most of the route above the upper reservoir so gaining visuals for route finding is very elementary.
Nothing extra is needed for summer hiking.
Ice axe, crampons are required in winter months