Starting from the junction with the Lamarck Lakes Trail (30E04)
, this trail climbs to the south up the side of the ridge, crosses the ridge, and contours into an unnamed drainage. The trail goes up this drainage and into, at about 12,200 feet, the drainage that empties into Upper Lamarck Lake. If you are descending this trail, be careful to bear right (south) here so as not to miss the trail, as a direct descent to the lake is very difficult.
The trail now works its way up the drainage going straight southwest toward the Col across open, sandy, and rocky terrain. This area can hold large patches of snow well into the summer season. There is a small tarn lake at the base of the Col and the last 150 feet or so of steep terrain below the Col often holds a snowfield that needs to be crossed with care. At the head of the drainage, be careful not to mistake the col on your left for Lamarck Col; it is not the right one and crossing it will take you into the Schober Holes Lake basin.
The descent from Lamarck Col is directly down on mostly sandy ground, interspersed with boulders and sand-dusted rocks. Once you reach the canyon bottom, the trail—obvious in places, and marked with cairns in others—runs along the north side of the lakes over a talus field and glacial moraine. Do not expect to move quickly through this area.
Once you leave Darwin Canyon and reach Darwin Bench, the trail offers a much less demanding tread. It is much easier to follow from the Bench down to its end at an unsigned junction with the John Muir Trail at the head of Evolution Valley.