Zooming in on Scouts at City Point

I've shared a few City Point, Virginia, Civil War photographic images over the past couple of months. These shots give students of the Petersburg Campaign a much better idea of the hustle and bustle surrounding the Army of the Potomac's supply base. This image is titled "City Point, Virginia. Scouts at Secret Service headquarters."

So were these men spies of sorts? Perhaps so. If so, imagine the adventures they had, the risks they took, and the stories they could tell of their ventures behind enemy lines gathering critical information.

The photograph prominently shows a group of four men, but zooming in on parts of the image lets us see many more details.

Two African American men dominate the foreground. They sit on logs, elbows on knees, while looking at the photographer. Both wear boots and civilian style slouch hats. They do not appear to have military apparel, as the man on the left looks to be wearing a civilian-style frock coat, while the man on the right appears to have on a civilian sack coat.

Zooming in on the man on the left's face, one can see his features, including his eyes, more clearly under the shade of his hat brim. He looks to be wearing a cravat, too.

Just behind the two seated men are two standing men. They are about as different from each other as possible. The man on the left is fully dressed, has a hat on, and sports a beard. The man on the right has his baggy trousers tucked into his boots, stands in his undershirt, and does not have a hat on. He is also clean shaven. The only thing these two seem to have in common is that they are both standing about as stiff as possible; probably taking a cue from the photographer to stand still while the image processes.

  

Looking closely, a line of railroad boxcars is visible through the tree branches in the left center of the image. These cars were part of the vital United States Military Railroad. 

The railroad line continues to the right center of the photograph where a flatbed car appears in front of a warehouse. The rail line runs right to the wharf where a side-wheel steamboat with protruding smoke stack sits in either the James or Appomattox River.

I seem to run into a curiosity in each of these "zooming in" shots. Are the cords tied to the tree branches something as simple as a clothes line or are they for something more significant?

In between the two standing men, and further in the background, one can see several lines or railroad tracks, a man standing with his hands in his pockets, and what appears to be an ambulance wagon. Other than the "U.S." on the top line, I am not able to make out the other words. Does anyone have a clue as to what type of conveyance this truly is?