With its new status and strategic location, Sacramento quickly prospered and became the western end of the Pony Express. Later it became a terminus of the First Transcontinental Railroad, which began construction in Sacramento in 1863 and was financed by "The Big Four"—Mark Hopkins, Charles Crocker, Collis P. Huntington, and Leland Stanford.
In 1850 and again in 1861, Sacramento citizens were faced with a completely flooded town. After the devastating 1850 flood, Sacramento experienced a cholera epidemic and a flu epidemic, which crippled the town for several years. In 1861, Governor Leland Stanford, who was inaugurated in early January 1861, had to attend his inauguration in a rowboat, which was not too far from his house in town on N street. The flood waters were so bad, the legend says, that when he returned to his house, he had to enter into it through the second floor window. From 1862 until the mid-1870s Sacramento raised the level of its downtown by building reinforced brick walls on its downtown streets, and filling the resulting street walls with dirt. Thus the previous first floors of buildings became the basements, with open space between the street and the building, previously the sidewalk, now at the basement level. Most property owners used screw jacks to raise their buildings to the new grade. The sidewalks were covered, initially by wooden sidewalks, then brick barrel vaults, and eventually replaced by concrete sidewalks. Over the years, many of these underground spaces have been filled or destroyed by subsequent development. However, it is still possible to view portions of the "Sa