(Ed.'s Note: Please excuse the use of the offensive "N" word, but the fact is that the terms was widely used here in the past. However, we have also heard that 1.) Black workers built the bridge, 2) that black soldiers camped here, 3) that black soldiers were hung there, and a myriad of other versions of how it got its name.
In the postscript by Schmelling above (click on graphic to enlarge), he gives lie to those versions and says the reference to blacks was the fact that when local Mexican workers were building it, they came in contact with black loam dirt and that they appeared to be black. Which version do you believe?
For a deeper treatment on the subject, see Bronsbil Estacion Javier Garcia's post at http://bronsbilestacion.blogspot.com/2015/08/legends-and-myths-from-nigger-bridge.html from which we took these graphics.)