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Well-wishers gather around Rep. George Miller, D-Martinez, following a press conference in which he announced his retirement in Richmond, Calif., on Monday, Jan. 13, 2014. Miller was first elected to Congress in 1974. (Kristopher Skinner/Bay Area News Group)

CONCORD -- Assemblywoman Joan Buchanan, D-Alamo, is endorsing rather than challenging state Sen. Mark DeSaulnier, D-Concord, for Contra Costa County's largest congressional district.

DeSaulnier hopes to succeed retiring Rep. George Miller of Martinez, who will leave office at the end of the year after serving 40 years in the House of Representatives.

District 11 encompasses north and central Contra Costa County, stretching from Richmond to Pittsburg along the shoreline and southward through Lamorinda, Walnut Creek, Concord, Pleasant Hill, Clayton, Alamo and Danville.

Buchanan had seriously looked at the congressional seat for herself. She and DeSaulnier both ran unsuccessfully in 2009 against then-Lt. Gov. John Garamendi for the neighboring congressional seat vacated by Ellen Tauscher.

State Sen. Mark. DeSaulnier. (Karl Mondon/Staff File)
State Sen. Mark. DeSaulnier. (Karl Mondon/Staff File)

Her departure from the District 11 field is the latest in a series of potential challengers who have instead opted to endorse the state senator.

"I'm pleased to support Mark DeSaulnier for Congress," Buchanan said in a prepared statement from his campaign. "Mark and I share a common goal of improving California's schools and making our K-12, community colleges and universities the best in the nation. I'm confident that Mark will be a strong advocate for our students and families in Congress."

The assemblywoman and former San Ramon Valley School board member will term out of office this year. Now that she has ruled out a congressional bid, she is expected to run for DeSaulnier's senate seat.

DeSaulnier terms out in 2016, but if he is elected to Congress this fall, a special election will be set for March 2015 to fill the remainder of his term.

Meanwhile, former Walnut Creek Councilman Kish Rajan, who said last week he was considering running for the seat, on Tuesday ruled out entering the race. Rajan left the City Council in 2012 when he was offered a job as the director of Gov. Jerry Brown's Office of Business and Economic Development.

"I love working for Gov. Brown and feel we are doing good things for the California economy," Rajan said. "So, I plan to stick with it."

Contact Lisa Vorderbrueggen at 925-945-4773, lvorderbrueggen@bayareanewsgroup.com, ibabuzz.com/politics or Twitter.com/lvorderbrueggen.