Because the rivers regularly flooded the young city, Sacramento raised the level of its downtown. From 1862 until the mid-1870s it built reinforced brick walls along downtown streets and filled the space inside with dirt.
The old first floors of buildings became basements, and the former sidewalks sank to basement level. Most storefronts were filled in, but many tunnels survive in Old Sacramento and the downtown area. The Stanford Mansion was raised twelve feet as part of the same response to flooding.