Where did most U. S. railroads exist in 1870? Why?

Most of the railroads were in the south because the south had to transport cotton to the North's factories

Railroad Maps, 1828-1900, a subset of Maps, is a collection of maps that represent an important ... can study the introduction of railroads to the United States and its impact, from its most fundamental ... Do the rail lines depicted on the map still exist today? ... Where trains did not run, stagecoaches continued to deliver mail.