When I first moved to San Francisco, I read the novella "Trout Fishing in America" by Richard Brautigan, a San Francisco author who died tragically young. I didn't realize it at the time, but he was a frequent visitor to this library and used it as a setting for his 1970 novel "The Abortion". A few years ago they had an exhibit of his work, letters, and relationship with the library.
The often copied palladian arch featured a central arched opening with two small side openings separated by columns. The renaissance palladian arch is actually derived from earlier triumphal arches as seen in the Roman Forum two thousand years ago. The drawing at the left is the palladian arch drawn by Palladio for the Basillica in Vicenza that was completed in 1617. Like all "good" architects, I traveled to Vicenza to see the master's work.
San Francisco didn't have the funds to cover the entire front with a granite faced palladian facade like the Basillica, but as is common in many public buildings, they put it where they thought it counts the most. Set against a brick background, this singular element contrasts nicely. For a neighborhood library, it's pretty grand.