More investigation and thought on whether the bridge in the old shot is the KCS or SP bridge across the Calcasieu River at Lake Charles/Sulfur and MORE from Agent 00-L:
Steve,
On further examination, I think that your photo is of the SP bridge.
The photo shows that it has three trusses, and the bridge currently has two. This aerial photo will show that the third eastern truss has been replaced by what is now a concrete trestle:
The old photo:
I don't believe that the bridge has been shortened, other than the replacement of the eastern truss with a trestle. Study the sat pics, and you will see that the bridge crosses the river between two natural river banks, and it has a long fill across the northern lobe of the lake. That fill has a trestle section near its eastern end. Understand that the land south of there, in the vicinity of the east end of the I 10 bridge and probably as far east as the east end of the beach is artificial landfill. Compare the shape of the north shore of the lake between the modern sat pics and the 1895 city map that I sent you.
My theory was that the bridge was put where it was because a long fill approach was going to be needed on the east side, and one could be dumped from barges on the lake more easily than hauled in on swampy land. The builders of the later KCS bridge had no choice but to use the latter method. Notice the configuration of its fill and trestle segments on the sat pics. That slightly crooked line through the swamp a bit north of the former KCS bridge is a power line right-of-way.
I have just found a looooong history of Lake Charles at http://library.mcneese.edu/depts/archive/ftbooks/haupt%20port.htm , but I see that's apparently where you found the bridge photo. This has the most thorough info yet on J. B. Watkins. Did you see that it says that he "built and operated a sugar refinery east of Lake Charles near the site that is now the Chennault International Airport"? He must have owned lots of land out that way.
It also says that he "built the first street railway system (the Steam Dummy Line) which ran north on Watkins [now Enterprise] Boulevard, then turned west on Broad Street to the lake." So, we now know for sure that the Dummy was his. This probably explains the double parallel lines on Enterprise and 1st. Enterprise was the ritziest residential street, and perhaps where Watkins himself lived. (After all, it was the street that bore his name.) The Dummy was needed for transport to downtown, schools, etc., but the classy residents wouldn't have wanted freight trains to and from the upriver sawmills and rice mill to run the median of their street.