1876-1900: Library of Congress
In the decades following the Civil War, the United States emerged as an industrial giant. Old industries expanded and many new ones, including petroleum refining, steel manufacturing, and electrical power, emerged. Railroads expanded significantly, bringing even remote parts of the country into a national market economy.
See the Gilded Age, from Wikipedia:
In United States history, the Gilded Age is described as the period from about the late 1870s to the late 1890s, which occurred between the Reconstruction Era and the Progressive Era. It was named by 1920s historians after an 1873 Mark Twain novel. Historians saw late 19th-century economic expansion as a time of materialistic excesses marked by widespread political corruption.
See the Gay Nineties, from Wikipedia:
The Gay Nineties is an American nostalgic term and a periodization of the history of the United States referring to the decade of the 1890s. It is known in the United Kingdom as the Naughty Nineties, and refers there to the decade of supposedly decadent art of Aubrey Beardsley, the witty plays and trial of Oscar Wilde, society scandals and the beginning of the suffragette movement.
Despite the term, part of the decade was marked by an economic crisis, which greatly worsened when the Panic of 1893 set off a widespread economic depression in the United States that lasted until 1897.