From context, this statement occurs during the Council of Elrond and following on from the stories of <PERSON>, <PERSON>, <PERSON>, <PERSON>, <PERSON> and with interjections from others.
It seems evident that it must be a reference to something in one of those stories, and the most probable event is <PERSON>'s invasion and ruin of Eriador in the Second Age, during which he killed <PERSON> and siezed the Rings of Power.
This is referred to in the description of <PERSON>'s story:
... many eyes were turned to <PERSON> in fear and wonder as he told of the Elven-smiths of Eregion and their friendship with Moria, and their eagerness for knowledge, by which <PERSON> ensnared them. For in that time he was not yet evil to behold, and they received his aid and grew mighty in craft, whereas he learned all their secrets, and betrayed them, and forged secretly in the Mountain of Fire the One Ring to be their master. But <PERSON> was aware of him, and hid the Three which he had made; and there was war, and the land was laid waste, and the gate of Moria was shut.
And is covered in more detail in the <PERSON> and <PERSON> material in Unfinished Tales:
When <PERSON> learned of the repentance and revolt of <PERSON> his disguise fell and his wrath was revealed; and gathering a great force he moved over Calenardhon (Rohan) to the invasion of Eriador in the year 1695 ..... At last the attackers broke into Eregion with ruin and devastation ..... But now <PERSON> attempted to gain the mastery of <PERSON>: Lórinand could wait. 381
But as he ravaged the lands ..... he called in therefore his scattered forces and marched west towards the land of Gil-galad, ravaging as he went.
And the aftermath, after the Numenoreans ("the great armament of Tar-Minastir") intervened:
Eriador was cleared of the enemy, but lay largely in ruins.
Aside from Rivendell (which was besieged), the major Elven stronghold - "the land of Gil-galad" - which <PERSON> was marching toward, was Lindon where the Grey Havens are, and Galdor is of course an Elf of the Havens.
<PERSON><PHONE_NUMBER> ..... At last the attackers broke into Eregion with ruin and devastation ..... But now Sauron attempted to gain the mastery of Eriador: Lórinand could wait. But as he ravaged the lands ..... he called in therefore his scattered forces and marched west towards the land of Gil-galad, ravaging as he went.
And the aftermath, after the Numenoreans ("the great armament of Tar-Minastir") intervened:
Eriador was cleared of the enemy, but lay largely in ruins.
Aside from Rivendell (which was besieged), the major Elven stronghold - "the land of Gil-galad" - which Sauron was marching toward, was Lindon where the Grey Havens are, and Galdor is of course an Elf of the Havens.
Sauron's ability to "torture and destroy the very hills" is therefore most probably a reference to the ruin of Eriador in the Second Age. 381