Where's Erkenbrand?

[Sharkû]

In the first Battle, Erkenbrand was still manning the Hornburg: "Erkenbrand of Westfold assumed command of the West-mark when news of the fall of Théodred reached him in the Hornburg on the next day." (UT, 3, V)
In the second Battle, he was still occupied when Isengard attacked again: "Erkenbrand did not at once himself proceed to the battlefield. All was in confusion. He did not know what forces he could muster in haste; nor could he yet estimate the losses that Théodred's troops had actually suffered." (ibid.)

Of course, "What followed is less clear, since only Gandalf had full knowledge of it. [...] on his return south to find Erkenbrand, he must have met Grimbold and Elfhelm [...] Grimbold's men he sent southward to join Erkenbrand…" A footnote quotes Gandalf from The Two Towers, III 8: "Some men I sent with Grimbold of Westfold to join Erkenbrand. Some I set to make this burial. They have now followed your marshal, Elfhelm. I sent him with many Riders to Edoras."

So the picture is that at first Erkenbrand was at the Hornburg, and then, at the time of the second Battle, he was south of the Fords, gathering troops and preparing. He then got reinforcements of in form of Grimbold and survivors and headed to the by now besieged Hornburg.

I have not found anything that tells of Elfhelm's late mission in Anórien. All we know is that he survived; I assume this small battle was not important to recount in view of the much larger events.