The huge expansion of rail lines in Midwestern United States during the 1850s had major economic and environmental effects. A. Construction of new rail lines into the Midwest had been effectively stopped by the Appalachian Mountains, but by 1850 improved construction technology had made further advances possible. B. Rail lines to Chicago and on to the East made it easier to get Midwestern goods to distant markets, while growing demand encouraged crop specialization and led to higher crop prices. C. Because of the growing volume of traffic coming by rail from the Northeast and Midwest, the value of goods arriving in New Orleans for shipment to markets abroad increased dramatically. D. Access to rail lines combined with the development of more-efficient farming equipment allowed a fertile land of the open prairies to be used for large-scale commercial agriculture. E. Reduction of annual prairie fires allowed trees to reappear, and native grasses were replaced by a few commercially grown plants as previously unbroken grasslands were divided into large fenced fields. F. Native Americans had grown corn on the prairies for years but had not produced large surpluses because the varieties they planted had far poorer yields than those introduced by commercial farmers.