I thought I'd seen the reference somewhere - the answer is Amon Lhaw, and it's practically the last sentence in FotR...
FotR, Bk2, Ch10, The Breaking of the FellowshipAt length (Frodo and Sam) came to land again upon the southern slopes of Amon Lhaw. There they found a shelving shore, and they drew the boat out, high above the water, and hid it as well as they could behind a great boulder.