Sourdough Mountain Trail

Overview

When open, Sourdough Mountain is a classic North Cascades sufferfest: about 10.4 miles round trip with roughly 4,870 feet of elevation gain to a high point near 5,985 feet. It’s steep, relentless, and incredibly rewarding—think sweeping ridge-top panoramas and a historic 1933 fire lookout at the summit. Expect 8–12 hours on trail depending on fitness and conditions.

Important note: as of late 2025, the trail from the trailhead to the lookout remains closed due to damage from recent fires. Check the park’s current conditions before you plan—this one is unavailable until further notice.

Trail Experience

From the Diablo side, you’ll grind through long forested switchbacks for the first ~3.5 miles before the grade eases into meadows. Around 4.2 miles you’ll reach Sourdough Creek and Sourdough Camp. Above that, subalpine meadows open to ridge views, and the final stretch to the lookout delivers the big North Cascades scenery you came for. Water can be scarce on the way up—plan to carry more than you think you need.

A longer, less steep approach via Pierce Mountain starts at the Ross Dam Trailhead. It meanders along Ross Lake before climbing through Douglas-fir and mountain hemlock to subalpine meadows, passing an old 1978 burn now grown in with grasses. Above Pierce Mountain Camp, early-season snow can obscure the tread; rock cairns help but routefinding skills matter.

History and What You’re Looking At

The lookout crowns a summit with deep park history: one of the earliest lookout sites (established in the 1910s), later rebuilt in 1933 and rehabilitated in the late 1990s. A poet once worked a season here as a lookout, inspired by the solitude and sweeping views. On clear days you’ll spot Diablo Lake below, sawtooth peaks all around, and subalpine meadows that light up with summer wildflowers.

Best Times to Hike

Typical season runs June through mid‑October, with snow lingering into early summer and sometimes returning in fall. Mornings offer cooler temps for the steep climb and better photography light over Diablo Lake. Midweek starts beat the crowds on popular summer weekends. In shoulder seasons, expect snow and plan for traction and conservative turnaround times.

Camping, Permits, and Regulations

Backcountry permits are required for any overnight stay. Designated sites include Sourdough Camp and Pierce Mountain Camp (small capacity; no fires—bring a stove). No camping at the lookout. Pets aren’t allowed on this route within the park. Much of this area lies in designated wilderness—stay on durable surfaces to protect fragile vegetation.

Alternatives While Closed

If you’re in the area now, swap in the Diablo Lake Trail for easier miles and big water views, or explore other lower-elevation trails nearby. Ambitious hikers might stitch together a long loop when access reopens by combining Sourdough with the Ross Dam and Diablo Lake Trails (about 20.5 miles total), finishing with a short road walk through Diablo.

Tips

• Start early; the grade is unrelenting and shade is limited higher up.
• Carry ample water and a filter; late-season sources can be low.
• In early season, expect snow, possible avalanche hazard, and tricky creek crossings—snow bridges can be undermined.
• Trekking poles help on the steep switchbacks.