A quick search of the "Big Database" of Phone Exchanges showed that the "HOward" exchange was used in Stockton, CA - just a few miles down the road from Lodi where I found this tray. A little more searching found an old photo of a place in Stockton containing this comment - "3300 N. El Dorado - Kelly's Car Wash - Former Silveria's Union Service (Manual Silveria was an Ex-Mayor)". I have no idea what the reference to Falmingo means - there is a sort of notorious niteclub in Stockton called the El Flamingo but it seems to be newer than this tray.

Thanks for the info - it was fun to search it out. Now Carol can put it out at the shop as a "local" collectible.