The trail to Deep Lake begins with a long and forested ascent toward Cathedral Pass — covering roughly 4 miles of trail with a gain of 2200 feet. There are two lakes along the way that can be nice spots to give tired legs a reprieve.
Just before the pass, the the trail hits a junction with the Pacific Crest Trail, and hikers hoping to reach Deep Lake should keep left. The lake itself should soon come into view below you as you start traipsing down a long series of switchbacks to reach the southern edge of Deep Lake.