I've only seen about two or three other trip reports for this mountain so I'll try and provide as much information as I can. Mount Bonnycastle is a remote granite bowl containing a massive cirque lake nested between the end of Indian Arm and the border of the Coquitlam watershed. Despite its remoteness, it can be easily seen from the city, especially up Indian arm/Say Nuth Khaw Yum. I found this peak just browsing maps of the area and have been obsessed with bagging it for the last couple years, there is no trail going up the mountain. Access involves a drive up to Squamish, driving down most of the Indian River FSR and taking the Hixon Creek branch until the gated boundary of the watershed.
Bonnycastle as seen from the Twin Islands lighthouse
The Indian River FSR seems to have recently been regraded and was in great condition compared to a couple years ago (still rough but no more landslide debris). The Hixon Creek branch was also surprisingly not too bad. My guess is the branch is maintained because of a pipeline running down the side of the road and plans to log part of Bonnycastle. We parked at the gate at followed Steven Song's GPS track (available on his website). As expected from previous trip reports we immediately ran into super dense second growth for about the first 100m until running into a steep bluff. If you find an easy way up this first bluff waypoint it! We ended up roping down on the way back unable to find an easy way down.
Initial second second growth section, almost nicer in some respect than old growth because of the lack of understory to wack through
Typical type of bush until the creek crossing
After passing the first cruxy bluff the we started to enter old growth forest. The understory thickened but wasn't bad to walk through. It looks like a large section leading up to the falls is scheduled to be cut. We found what looked like fresh flagging for a falling boundary and spray painted trees. While I'm not in favor of cutting more old growth in an already heavily logged valley, logging might improve access up the mountain (new road?), or just make it too dense to hike through only time will tell.
The section just before the creek turned out to be some of the worst bush. Dense thickets of blueberries and meandering around devils club made reaching the creek a bit of a slog. Once we reached the creek-side the forest opened up a bit and we encountered the impressive falls. Here we stopped for a quick lunch break and planned where to enter the forest. We decided to enter a bushy section which seemed to be the least steep section of the opposite bank. We ended up having to do some sketchy traversing to get out of creek gully, this would be where we would rope down on the way back as well.
The waterfall was massive!
After crossing the creek the terrain becomes quite different. The steep dense old growth seemed only to get steeper and steeper as we got closer to the top of the falls. We pulled ourselves up using small trees and other shrubs, welcoming any fallen logs that could be walked across.
Starting to get a little airy
Steeper and steeper
Once at the top of the falls the steepness reaches it's max with bluffs started to form narrowing our options. We explored a steep creek beside the falls that seemed to bluff out further up. Back to the bluffs we found a rockless passage to climbers left which seemed to be the best of the worst of our options, it required some careful bush climbing to ascend. After this second crux the grade lessons as well as the bushwacking. Eventually we ran into the creek that had been beside the falls. The creek was a nice change in terrain and made for way faster travel until it started shooting off too far to the NW. Re-entering the bush we came to our third cruxy bluff. Following it climbers left we opted for a log crossing a steep gully that led us into some blueberry thickets above the bluff. Once above this third bluff the bush became its thickest. We started to trek through stunted sub-alpine trees and again dense blueberries.
By far the worst bush yet
The swearing started and we opted to just plow through to the lake instead of looking for less dense shrubbery. We did manage to get lucky sometimes popping into small meadow refuges.
Almost brought a tear to my eye at this point
Finally we reached a small slab before the lake and opted to climb it instead of bashing our way around it and, at the top, was greeted with our first views of Barnes lake.
The crystal blue water of Barnes Lake
Trying not to think about bush
The lake was jaw dropping and definitely worth the struggle to get there. The terrain around the lake was a little bushy but had lots of nice alpine meadows crisscrossing the area. We set up camp on one of the few flat spots around the lake and enjoyed the views. The lake was freezing but super refreshing on a 30 degree day. Some baby salamanders could be seen swimming around the lake shore. The best camping spot (as seen from our spot) seemed to be next to the SE ridge but would involve crossing the lakes outflow. The shape of Bonnycastle wrapped around the lake allows you to echo your voice about 6 or 7 times.
Some Gucci terrain
Resting for tomorrows bag
We packed up among the bountiful morning mosquitoes and hiked to a large boulderfield under the NE ridge. Here we left all our heavy items and pressed on up the talus'y creek. The grade became steeper and steeper and forced us to eventually follow the creek up or a dry boulder field. We opted for the boulder field which led to an incredibly steep, wet and sketchy mud staircase. Learn from our mistake and take climbers right up the creek! Eventually we veg pulled our way up the steep mud hill and ended up on the creek further up. Here the area opened up into some really nice meadows and a huge boulderfield.
More and more boulders the farther up the ridge we go with a nice view of the seemingly hanging Barnes Lake
Following the GPS track we found a ramp type feature that bypassed the steep cliffs overhanging the boulderfield. The ramp wasn't bad at all and is super noticeable higher up. The ramp led us up to Bonnycastle's NW ridge and we got our first views of Meslilloet Mountain. The track followed the high point of the ridge but this looked like a lot of bushy scrambling, so we opted to go on a flat section behind the ridge which eventually led to an easily accessible hill just before the summit. The ridge before the summit looses some elevation and leads to a bit of scrambling up to the peak bump.The scrambling wasn't too bad but did involve skirting some wet sections and snowpack. After scrambling it's just a leisurely walk to the top. There was lots of goat fur and tracks up here but no goats to be seen..... At the summit was a small cairn marking Bonnycastles high point. Water wasn't an issue for us since north facing snow packs and small tarns seemed to feed many meandering streams on the approach.
Summit Pano with Meslilloet in the middle
Cairn and eastern Coast Mountains
Tarn below peak and Disappointment Lake not looking disappointing at all
We descended back down the bowl picking up the gear we stashed and opting not to go for another swim in the lake since it was getting late. The bushwhacking down was as expected, and many slips were had in some steep sections. We refreshed at the creek and bushwhacked towards the road finally breaking out to the car. We packed up as the Coquitlam watershed security watched us behind the large chain link gate, ensuring we didn't decide to book it into their area.
The beauty of Bonnycastle definitely made the sweat and scratches worth it. While I probably won't be going back anytime soon, it's a great trip for anyone feeling real adventurous.