Map of our track up Basin Mountain. Cross the talus on the south side of the lake then follow the use trails along the east side of the creek to the lower lake. Scramble up through the talus to the second lake at around ~11.4k. From this lake head towards the north ridge, and just before hitting the ridge turn south to the summit. It's an easy class 2 route right up to the summit block which has a little borderline class 3 exposure but is still really easy.
We tried to go around the other side of the lake on the way back but couldn't find a path through the marsh and bushes. Also: there are two chutes that look like they might go from the lower lake straight towards the summit. We didn't investigate since they looked steep and we had no beta. But they might go and help cut down on distance (not that this is a super long climb...)