Industrial activity near the downtown area has been concentrated along the railroad yards of the Mill Creek valley. The earliest railroad construction here was the Pacific Line which ran westward from a station at Seventh and Cerre Streets. It was constructed through the valley area in 1853 after the drainage of Chouteau's Pond, which stretched west as far as the site of Union Station. Other lines were built north and south along the river before the Civil War. Railroad activity increased considerably with the opening of Eads Bridge and its tunnel in 1874, followed by the First Union Depot at Twelfth and Poplar Streets in 1875. Another rail link was forged in 1889 with oompletion of the riverfront elevated railroad to Merchants Bridge. The old Union Depot was replaced by the present Union Station in 1894. The area which is now covered by the Jefferson National Expansion Memorial Park was formerly a warehouse and industrial district. It was active as such from about 1840 to 1890 when its decline began with the cessation of steamboat traffic on the Mississippi River.