The 6-cent Bas Obispo — Before commemorative (Scott 124) of the Canal Zone Twenty-fifth Anniversary Series appeared on August 15, 1939. The series includes scenes significant to Canal Zone history, eight titled 'Before' and eight titled 'After.'
The 6-cent stamp features a view taken in January 1910 of the diggings at the old French town site of Bas Obispo, near the intersection of the Chagres River and Gaillard Cut. The view looks south towards the Pacific and shows some of the trains and steam shovels moving soil from 'The Cut' on their way to disposal sites.
Though it had no specific function, patrons sometimes used the 6-cent stamp on double-weight ship mail letters and with other stamps to pay for postal services such as airmail or registration. Nonetheless, usage was rare since so few of these stamps (198,000) were issued and only about 68,000 sold. Collectors used many on first day covers, of which Walter G. Crosby produced many. Remainders were withdrawn from sale on February 28, 1941, and destroyed on April 12.