The Valley of Jehoshaphat

In Joel 4.12 (or 3.2 dependent on your translation), there is a reference to the “Valley of Jehoshaphat.”  Here’s the comment from the The IVP Bible Background Commentary: Old Testament (which if you didn’t know by now, I love):

There is no valley with this name known in Israel from the Bible or from other sources, or even from tradition. The alternatives are (1) that the reference is being made to a valley that had something to do with the ninth-century king of Judah by the name of Jehoshaphat (the only mention of a valley in his account is in 2Kings 3); or (2) that the valley’s name accords with what takes places there (the name Jehoshaphat means “Yahweh judges”). If the latter is the case, as many commentators have concluded, the location would likely be one of the valleys surrounding Jerusalem.