The Los Angeles Union Station Collection contains detailed records of the planning and construction phases of the project, primarily between 1930 and 1940. Most of the records are composed of correspondence between railroad executives as well as a large number of blueprints and maps for the project. While the collection has been re-housed in new folders and boxes, the materials were generally left in their original order and reflect the original filing system used at the station. As a result, folder titles and sequence appear as they did in the original files.

Beginning in the late 1920s, items in the collection document the railroad companies' legal battle to avoid construction of the station, disagreements amongst the railroads on the location and design of the terminal, as well as large number of blueprints and maps for station buildings, tracks, and surrounding areas. The most detailed records document each stage in the construction of the terminal building as well as a significant number of documents from the project's legal department. The construction files include a large number of blueprints of different sections of the terminal building as well as surrounding infrastructure (primarily street improvements and bridge construction). The construction portion of the collection also contains a substantial number of specifications for portions of the project given to subcontractors as well as information on subcontractors and vendors. The legal files in the collection include a significant collection of correspondence from the LAUPT legal department, almost 200 files on personal injury cases brought against the station, as well as a large collection of contracts signed between LAUPT and subcontractors, vendors, and lessees.

Smaller portions of the collection include files from the project's architectural committee, records of personnel issues, agreements with the City of Los Angeles, documentation of the land acquisition and vacation process, information on the U.S. postal facility constructed in conjunction with LAUPT, and agreements with local light rail companies.