Description

The former Mark Twain Memorial Bridge, spanning the Mississippi River between Hannibal, Missouri and Illinois, was constructed as a Public Works Administration (P.W.A.) project.

A preserved portion of the old Mark Twain Memorial Bridge remains on the west bank of the Mississippi River in the Cardiff Hill Overlook Park, A plaque exists in some concrete railing preserved in place and notes its Federal Emergency funding and was Project No. 3624. The bridge was formally dedicated by President Franklin D. Roosevelt. It served traffic from 1936 to 2000 when it was demolished and replaced by a truss bridge to the north to accommodate I-72 traffic.

Bridgehunter.com give additional details:

Opened Sept. 4, 1936; tolls removed Oct. 30, 1940; rehabilitated 1982; replaced and demolished 2000.
Builders:
Mt. Vernon Bridge Co. of Mt. Vernon, Ohio (Superstructure)
Sverdrup & Parcel of St. Louis, Missouri (Designer)
Union Bridge Co. of Buffalo, New York & Athens, Pennsylvania
(Substructure)
Design:
Subdivided Warren continuous through truss
Dimensions:
Length of largest span: 626.8 ft.
Total length: 3,507.0 ft. (0.7 mi.)
Deck width: 23.9 ft.
Vertical clearance above deck: 14.2 ft.