From Boston Basin, ascend along the left (North) side of the Quien Sabe glacier until you reach the base of Sharkfin Tower between the summits of Sahale and Boston Peak. Traverse South along the base of the rock face until you reach the col. The glacier is steeper here and be sure to watch for crevasses. Traverse exposed snow to reach the loose class 3 summit scramble. Watch out for a cornice that lasts into early summer.
From Marblemount, drive east on Cascade River road 21.7 miles to the fork. At 3200 feet, follow the abandoned Diamond Mine road for .75 miles and then follow the trail across 4 stream crossings over the next half mile. There are camping sites at a little over 5000 feet and 6000 feet with compost toilets. To get to the basin it is a 3 hour hike on a unmaintained climbers trail. Boston Basin is a very popular location for climbers because of its beautiful scenery and alpine grandeur.
A few Slings for the 4th/Mod 5th class summit block, maybe a few pickets for the steeper snow sections.