Facing a nearly $7 billion potential loss this fiscal year, The United States Postal Service selected 677 branches nationwide for either closure or consolidation, including more than a couple dozen in the Bay Area. Threatened post offices in San Francisco are the Civic Center P.O. Box Unit, the Federal Building, and the McLaren branches. Thanks to electronic communication, mail volume decreased by 9.5 billion pieces last year and is expected to fall by 28 billion pieces this year.