Ron,
William A. Frassanito has published and described the post-battle photographs taken in the vicinity of Devil's Den/Valley of Death/Slaughter Pen. For instance: Early Photography at Gettysburg, pp. 284-293, shows a group of six Confederate dead scattered inside the woodline - I believe these men to be from the 44th Alabama. Also see: Gettysburg, Then and Now, pp. 23-24; and Gettysburg, Then and Now, Companion, p. 19. Now that the Park has restored the terrain to its 1863 appearance, it is much easier to identify the exact locations where these photographs were taken, and walk the hallowed ground.