In the Trailer:

http://www.youtube.com/watch?feature=player_embedded&v=1nDB-A1zW9s

Pay attention to 1:14... ?where is this Forest area located with the stone heads lying in the ground?

Crap, was just there! Give me a second to remember (Too lazy to start up Skyrim)

EDIT: Look around Pinewatch...

Ok, let me check hehe thanks.

Since the trailer showed the major holds first(markarth, that foresty area, windhelm, whiterun, solitude) then bleak falls barrow, i think the forest area might be Riften.
But i see no riften city there, which confuses me too.
I ran around Pinewatch but i cant seem to find that particular area. Guess its a mystery

i thought it was around falkreath

I thought that the forest was in Falkreath as well - just wander around the areas near Helgen, Falkreath and Riverwood and you'll find it (or something very similar)

I think it's one of the trails south of Falkreath that lead up to the area where Angi's cabin or Bloodlet Throne are located. I don't see Shriekwind bastion in the distance though, which is always clearly visible in the distance. The forest trees are definitively from the Falkreath area.

Except that the Rift is about 99% Fall Forest, and that's clearly Pine Forest.

It's somewhere near Falkreath for sure.

Looks like Falkreath. Slight chance it could be where eastmarch/rift/whitren holds meet just past Valthiem Towers but it's more likely the former.