The definition of ephemera is "something short lived or transitory." Paper ephemera, either printed or manuscript, is produced for a specific purpose and is intended for disposal. Advertising material, blotters, business cards, calendars, forms and signs, postcards, postcards, posters, stationery, tickets, and travel passes are examples of the types of ephemera the Library collects.

The Library also has ephemera relating to industry associations and labor unions, fairs and events, and railway and technology museums. An extensive set of California rail enthusiast organization by-laws, membership lists, and excursion announcements complements the information available in the Library's holdings of club newsletters. Subject files cover topics such as movies, miniature railroads, hobos, and railroad terminology. The Library also has information about notable railroad-related personalities, including artists, writers, photographers, and collectors.

For the most part, ephemera has not been individually catalogued nor entered into searchable databases. Each document type is arranged by corporate name, and may be further subdivided by subject, date or personal name.