Cathedral Basin to Monica Lake

Cathedral Basin to Monica Lake is a 9.7-mile out-and-back from the Linda Lake route junction at Lake O’Hara, continuing past Cathedral Lakes to a small alpine lake beneath Cathedral Mountain. Allow about seven hours on the route, plus the approach from Le Relais. Monica Lake is a special payoff, but the upper climb is very steep and the tread gets faint; choose this only if you are comfortable finding your way across rough alpine ground. Cathedral Prospect is a shorter turnaround, with the lake visible below.

The route begins at the Linda Lake Route junction beside Lake O’Hara Campground, follows the trail toward Linda Lake, then joins the maintained Duchesnay Basin approach to Cathedral Lakes. A bridge crosses the lake outlet, with Vera Lake visible downstream. The maintained trail ends at the sharp right turn for the Cathedral Basin Alpine Route; from there, you are on a rougher continuation, not a signed day-hike path.

The route climbs hard beside a slope of scree and talus, on small, steep turns. Higher up, the grade eases and the line traverses east across a rockfall field. Old red-orange blazes have faded and several tracks braid through the boulders, so route-finding is part of the hike. If you lose the line, stop and reassess rather than following an attractive track toward a different basin or summit.

Monica Lake sits below Cathedral Mountain at the mouth of Duchesnay Basin, in a small cirque ringed by larches. Cathedral Prospect gives a broad look back over Lake O’Hara, with the lake tucked below the mountain. At Monica, frame the water with a strip of foreground boulders and the rock walls above; that shows how small the lake is beneath the cirque.

The nearby Cathedral Lakes are kettle ponds: blocks of glacial ice were buried in debris, then melted and left the shallow basins. Across Duchesnay Valley, Odaray Mountain’s northeast ridge rises as a roughly 900-metre rock buttress. In peak bloom, the meadows hold paintbrush, lousewort and valerian.

Lake O’Hara access is managed. Reserve the day-use shuttle ahead; it stops at Le Relais, and the Linda Lake route junction is farther along the trail network. Without a shuttle reservation, the access road is an 11-kilometre walk each way. Le Relais has seasonal trail information, hot drinks and snacks, separate from this route. Leashed pets are allowed in the backcountry, but they cannot ride the shuttle or enter the campground. Higher routes can remain snowbound and avalanche-prone into late June, so check conditions before setting out.