Democratic presidential candiate Barack Obama is about to open his first regional campaign office outside the four early primary states (Iowa, New Hampshire, Nevada and South Carolina) on Sunday right here in Oakland — two blocks from where Democratic presidential candidate Hillary Clinton is scheduled to stage a big rally a few hours later. No, he won’t be here himself.

It hadn’t been lost on journalists or political observers that the Obama operation in California thus far has been almost exclusively grassroots; there’ve been some trainings and events, but not much in the way of professional staff or offices.

Former gubernatorial candidate and state Controller Steve Westly told me today that Oakland was chosen for the office because the junior Senator from Illinois enjoys a broad base of support in the Bay Area and Northern California — remember the 10,000 to 12,000 who turned out for his March 17 rally in Oakland? — and expects that widespread backing by minority and young voters will carry him to victory in the Golden State. Oakland represents the kind of ethnically, socio-economically and otherwise diverse audience to which Obama appeals, Westly added, and efforts have been underway for weeks to secure a location; it turned out to be 436 14th Street, not far from Frank Ogawa Plaza.

But Westly wouldn’t comment on whether it’s coincidence that the office will open at 1 p.m. Sunday, three and a half hours before Clinton’s “Club44 Block Party” is to begin on Clay Street between 12th and 14th streets. “Who knows?” he said.

The Obama campaign also today announced an expanded California staff, including communications director Debbie Mesloh; she’ll be on leave from her post as communications director for San Francisco District Attorney Kamala Harris, herself an avowed Obama supporter. Mesloh previously worked as Northern California Field Director for U.S. Sen. Dianne Feinstein, D-Calif., and as press secretary for the Atlanta City Council.

Other hires include: