California Democratic Rep. Dennis Cardoza announced Thursday that he will not seek reelection in 2012, a move that makes him the latest moderate Democrat to head for the exits.

“I love the people of the Central Valley, and thank them for the confidence they have placed in me for over 20 years of elective office,” Cardoza said in a statement. “While I plan to retire from public service after this term in Congress, I will energetically continue my efforts to improve California as a private citizen.”

About half of the House’s moderate Blue Dog Democratic caucus either lost or retired in 2010. Of the remaining two dozen, most of them are either retiring or facing tough reelection races post-redistricting.

Cardoza’s exit comes as little surprise, but his move does add some clarity to a still-blurry picture about who will run where in California.

The state’s new Citizens Redistricting Commission has severely overhauled the congressional map, causing a number of incumbents to make tough choices about which new districts they will run in.

Cardoza was drawn into the Democratic-leaning 16th district with Reps. Jim Costa (D) and Jeff Denham (D). His move means Costa will almost definitely run in the 16th rather than the more competitive 21st, while Denham will probably run in the Republican-leaning 10th.

Both sides have already landed recruits for the 21st, though, as state Sen. Michael Rubio (D) and Assemblyman David Valadao (R) are running.

Cardoza is the sixth House Democrat to announce his retirement, while eight others are running for other office. Republicans have no outright retirements so far, but six members are running for higher office (including Rep. Ron Paul, who has said he won’t seek reelection to his Texas House seat after his presidential campaign).