Robison Mountain is a mountain of modest altitude deep in the Diablo Range of Northern California. Though not well known, its a profoundly isolated summit deep in the heart of the Orestimba Wilderness. It's utter inaccessibility outside of the annual Backcountry Weekends in Henry Coe State Park made it a sought after prize for this Bay Area Peakbagger. So over the April 2026 weekend, I did a massive loop of the wilderness, including a successful bag of Robison Peak.
I wrote about the backpacking trip in a previous post but I wanted to give some updated information on this particular leg of the trip.
Robison Peak Overview
Robison Peak stands at 2,662', very humble by the standard of California coastal peaks. It's dwarfed by its higher neighbors such as Copernicus Peak (4,385'), Challenger Peak (3,853') and Mt Stakes (3,809'). But it is isolated and prominent. This peak is essentially the centerpiece of the vast Orestimba Wilderness in the far northeastern section of Henry Coe State Park.
Curiously, Robison Peak doesn't show up on any major peakbagging lists. But for anyone seeking rugged solitude, it's as good as it gets in this part of California.
Access & Trailhead: The best trailhead for Robison Peak is Orestimba Corral. This is a parking area that's only open during the annual Backcountry Weekend occurring each April. Be sure to contact the Pine Ridge Association by January to reserve a spot and pay for your ticket. Let them know you're backcountry camping if that's your plan. The cost was $100 when I did it in 2026.
Distance & Elevation: Done as a straight out-and-back, this is a grueling 20-mile trip. Note the trail becomes very rough an ambiguous from the Rooster Comb Trail on to the summit. The "Robison Peak Trail" itself doesn't exist in any discernable way. Prior fires and no recent trail maintenance makes much of the mountain a bushwhack rather than a hike. I strongly recommend bringing a pre-loaded GPS. I also recommend at least 2 days for the route.
Here's a rough idea of the route I took. I also noted some options for backcountry camping:
Hazards and Considerations
The hike is practically only done in the spring. Water seems abundant, or at least it was in April 2026. Orestimba Creek was a consistent source. But there's no real water sources past the Rooster Comb Trail to the summit unless dropping back down to Orestimba Creek. I used a standard backpacking water filter and was fine.
Tics are considerable but Lyme Disease is not very common in this part of California. Of course, other tic-borne diseases exist and I wore 100% Deet at all times.
Mountain Lions are the biggest predatory you could theoretically encounter and its doubtful you'd ever see one. Black bears don't inhabit this part of California.
Services: There are no services in this part of the park. Rangers regularly patrolled Orestimba Creek Trail but past that there was nobody. Cell phone reception was not dependable. Ridgelines and mountain tops had some reception but most of the wilderness did not. Don't expect an easy rescue if you get into trouble.
Bikes are not allowed in the wilderness — There is no feasible way to cut the effort or distance down by biking.
Trip Report
Approach
Starting from Orestimba Corral, I followed Orestimba Creek Trail for about 5 miles to the intersection with Red Creek Trail. Orestimba Creek Trail is basically a ranch road but there were about a dozen water crossings. All could be easily made and I didn't need to take off my boots. The trail undulates over the hilly country that defines Henry Coe State Park but there's no sustained gain between the corral and Red Creek Trail.
From here, I walked about 0.6-miles to the Rooster Comb Trail. This is a necessary detour to avoid trespassing on guarded private land. Had I not noticed a ranger showing the way, I would have missed the cut-off trail. The Rooster Comb Trail itself was arduous and very overgrown. Its about 2.6 miles with lots of gain/loss to the start of the Robison Mountain Route.
Robison Mountain Trail Route
At 8.3 miles from the trailhead, I reached the route going up Robison Mountain. There was neither a sign marking the turnoff nor any sign of trail-maintenance in the last decade. I might has well followed a straight line up the mountain from there.
Everything was just varying difficulties of bushwhacking to the summit. The slopes leading up to the ridgeline were awash in chamise. At times I felt like a battering ram — there simply wasn't a way around it. My pace slowed to about 1 mile per hour. It is about 1.7 miles of 20% grade from the turnoff to the ridgeline
Gaining the ridgeline was a relief but not the end of the effort. The ridgeline is nearly the same altitude as the summit but there was thicker brush and plenty of up-and-down before the top. Effort-wise, it's the midpoint. The brush is thicker and the route-finding is challenging given there's several sub-summits of equal altitude.
At about 0.3-miles from the summit, I took a sharp left and gained the final hundred feet. Snodgrass Lake was on the other side — a curiously riparian area at a relatively high elevation. It's unclear to me whether its a natural lake or one of many reservoirs doting the Henry Coe landscape.
Finally on the summit, I marveled at the views and the relatively empty summit register. The last named signed was from 2024 and I wouldn't doubt the mountain goes years without visitors.
Descent and Final Notes
Like any bushwhacked summit, the descent is no easier. Another round of difficult route-finding and wading through scrub and overhead chamise. It took just as long to get back to Rooster Comb Trail as it did to climb the mountain.
My eventual route took me north and up towards nearby Mt Stakes. For those returning after the summit it's retracing the steps back to Orestimba Corral. The final 5 miles between Red Creek Trail and the Corral are disheartening as you gain all the ups-and-downs back to the trailhead.
Robison Mountain is the most lopsided effort-to-altitude hike I've ever done. Glacier travel would have been more straightforward than this far-flung bushwhack. Why we peakbaggers do such things is surely a mystery.
No Comments