In 1933, Flewelling designed the Beverly Hills Post Office, the first Federal Works Project Facility, which today is listed on the National Register of Historic Places.

Its design emulated the Romanesque style of the early Italian Renaissance whose outward appearance required construction materials (concrete, brick and terra cotta) that were readily available in Southern California. The architectural detail for the interior lobby was simplified, creating a modern atmosphere. The craftsmanship of marble work, of moldings and cornices, and of ornamental metal that formed the lobby screen grilles was as much a credit to the dozens of skilled artisans as it was to Flewelling’s vision. He acknowledged the outstanding craftsmanship as “unusual in this age of mass production.”