Definition of "Pittsburg"

I never see a shivering, white-faced wretch in the prisoners’ dock that I do not hark back with shuddering horror to the strange events on the Pullman car Ontario, between Washington and Pittsburg, on the night of September ninth, last.

1909, Mary Roberts Rinehart, “I Go to Pittsburg”, in The Man in Lower Ten, New York, N.Y.: Grosset & Dunlap, page 1