Lost GPX file so had to draw it out. Much more strenuous than the 17 miles (GPX file read ~25 miles) and 5000 vertical feet described. First and last 6 miles (on trail up to Lamarck Col and down from Muriel Lake) are fine but everything in between is scrambling, talus, shale, route finding. All class 3, sometimes having to take off packs etc. Still worth it for the views of Darwin Canyon if you don't have time for the 55 mile North Lake to South Lake loop. Doable in 3 days but don't underestimate the route finding/talus/boulder fields.