The South Slope route is the easiest way to climb Mt. Gabb from Lake Italy. Numerous variations of the route exist, but all start from the vicinity of Lake Italy and aim for the broad, sandy slopes located south of the peak and northeast of an unnamed ridge that juts out from the Mono Divide. The final scramble to the peak can be anywhere from class 2 to class 3, depending on your preference.
Hike to Lake Italy. Consult the Getting There section for more information. You can find several good places to camp at Lake Italy, including the west and southeast ends.
We can consider the South Slope route in three stages.
Up From Lake Italy
Hike/scramble from Lake Italy to the beginning of the south slope. Aim for the sandy slope that leads up to Mt. Gabb's southwest ridge. From the west, this slope will be hidden behind what we'll call the "south slope ridge," a southeast-trending ridge located south-southeast of the summit. Note that the "south slope ridge" does not lead to the summit and should not be confused with the southwest ridge, which does lead to the summit.
Although not obvious from the topo map, various small cliff bands guard the south slope from the north shore of Lake Italy, but you can easily circumvent them. If you are coming from the east side of Lake Italy, you can head upward from the vicinity of Toe Lake over easy slabs and benches. Those coming from the west can head up along a small creek and aim to top out below the "south slope ridge." (Going too high will lead you into some unnecessary talus-slogging.) Either way, this section is a mix of pleasant low class 2 and trail-less class 1.
Hike up the sandy slope on the northeast side of the "south slope ridge." For the most part this section is just a walk-up.
To the Summit
From the sandy slope you have three main options:
Southwest Ridge: Walk up the sandy slope until it terminates in the southwest ridge, and follow the ridge to the summit. This route features some large boulders but is still class 2. Some rocks are loose, but enough are solid to make this is a fairly pleasant scramble.
Southwest Slopes: Head up the sandy slopes below the southwest ridge. This is easier than the southwest ridge in the sense that it requires less frequent use of hands and probably less exertion, but it is also rather loose and not particularly fun. Consider it as a descent route.
South Side: If you leave the sandy slope sooner and head up the south side of Mt. Gabb, the scrambling is reportedly class 3. Please leave a comment if you can provide more information about this option.
None needed if you are doing this route in summer.
"When choosing between two evils, I always like to choose the one I haven't tried before."