At the Paley Center's 2013 New York television festival, David Duchovny announced that he didn't want Gillian Anderson to work on the show because he wanted to preserve the memory of their partnership on The X Files.
In response of multiple voices asking him to invite Gillian Anderson to guest staring in Californication as a Hank's lover, Duchovny always affirmed that he'd never do it because he wanted to preserve their special relationship as Mulder and Scully.
"Californication" is a portmanteau of 'California' and 'fornication'. Its origin is bumper stickers in Oregon in the late 1970s and early 1980s that read "Don't Californicate Oregon". Red Hot Chili Peppers' 1999 album "Californication" sold over 15 million copies, and as of 2009 is their most successful record.
According to David Duchovny, ever since the show moved from being aired in the fall to being aired in the spring, creator Tom Kapinos has written every season finale as a possible series finale. This is because the shooting schedule hasn't changed that much, so when the show premieres in January, the season has been shot for months.
The poem, printed on a poster, one can see in the intro is from Chinese poet Li Po (Li Bai): Facing Wine Never refuse wine. I'm telling you, people come smiling in spring winds: peach and plum like old friends, their open blossoms scattering toward me, singing orioles in jade-green trees, and moonlight probing gold winejars. Yesterday we were flush with youth, and today, white hair's an onslaught. Bramble's overgrown Shih-hu Temple, and deer roam Ku-su Terrace ruins: it's always been like this, yellow dust choking even imperial gates closed in the end. If you don't drink wine, where are those ancient people now?
The opening episode to season 4 shows Hank's mugshot in the book store window with Mia's face publicizing the underage affair they had. There is no cut on his cheek, like he had when he was taken into jail. However, this is because the mugshot is from his season 2 arrest for assaulting an officer.