The Keystone View Company (1892-1978) was a major distributor of stereographic images first opened in Meadville, Pennsylvania. By 1905 it was the world's largest stereographic company. By the 1920s the Keystone Company was the sole surviving major producer of conventional card-mounted views anywhere in the world. They had offices in London, Paris, Sidney, Capetown, Rio de Janeiro and Tokyo. In 1978, the company's records and inventory of negatives were donated to the UCR/California Museum of Photography at the University of California Riverside, where they are now known as the Keystone-Mast collection: https://calisphere.org/collections/11747/

https://stereoscopy.blog/2021/01/03/keystone-view-company/

https://en.wikipedia.org/wiki/Keystone_View_Company