Wisconsin's farm interior to the port. By 1862 Milwaukee was the largest shipper of wheat on the planet, and related industry developed. Grain elevators were built and, due to Milwaukee's dominant German immigrant population, breweries sprang up around the processing of barley and hops. A number of tanneries were constructed, of which the Pfister & Vogel tannery grew to become the largest in America. In 1843 George Burnham and his brother Jonathan opened a brickyard near 16th Street. When a durable and distinct cream-colored brick came out of the clay beds, other brickyards sprang up to take advantage of this resource. Because many of the city's buildings were built using this material it earned the nickname "Cream City," and conversely the brick was called Cream City brick. By 1881 the Burnham brickyard, which employed 200 men and peaked at 15 million bricks a year, was the largest in the world. Industrialization Flour mills, packing plants, breweries, railways and tanneries further industrialized the valley. With the marshlands drained and the Kinnickinnic and Milwaukee Rivers dredged, attention turned to the valley. In 1869 an initiative was undertaken to channelize the Menomonee River and build a series of ship canals, which included Kneeland's Canal, Holton's Canal, Menomonee Canal, South Menomonee Canal and Burnham Canal. Part of South Menomonee Canal, Menomonee Canal, Kneeland's Canal and Holton's Canal have since been filled in, and Burhham canal is no longer navigable after extension of 11th St. with street level bridge in mid 1980s. Unimaginable amounts of fill came down from the bluffs to raise the valley floor an average of and lower the north rim by as much as . The steep inclines of the valley walls were softened, and more rail lines were put in. By the turn of the 20th century, the once natural marshlands teeming with wild rice, and water fowl was all but forgotten. The first viaduct was completed in 1878 along 6th Street. It was later replaced in 1908 and again in 2002 with a photogenic design-build cable-stayed span touting dual bascule bridges. Other crossings followed with the 16th Street Viaduct in 1895 (replaced in 1929), the 27th Street Viaduct in 1910, and the 35th Street Viaduct in 1933. By 1879 meat packing became the most important industry in the city, and the Menomonee Valley was a critical supply point for the likes of John Plankinton, Frederick Layton and Philip Armour.