In what part of the country where the first railroads built by 1890 other parts of the country was densely covered by railroad tracks?

By 1890, the northeastern United States, particularly areas like Pennsylvania, New York, and New Jersey, was densely covered by railroad tracks. This region was a hub of industrialization and urbanization, facilitating the movement of goods and people. The development of railroads in the Northeast set the stage for expansion into other parts of the country, including the Midwest and the West, as rail networks continued to grow.