that the waters which came down from above stood, and rose up in one heap, a great way off, at Adam, the city that is beside Zarethan; and those that went down toward the sea of the Arabah, even the Salt Sea, were wholly cut off: and the people passed over right against Jericho.
The waters standing up in a heap is, of course, exactly what waters always do behind a dam, and, since this miraculous stoppage took place miles above where the Israelites were, they might not have known exactly where the waters were gathered together in a heap until some time later. Joshua's knowledge of this came in advance from a direct revelation of God. Significantly, the place identified as Adam is the precise location of the tallest of those great mud cliffs that line the banks of the Jordan.