Two of the most exciting new CD's out of California could be described as underground hip-hop, though they have almost nothing else in common. And maybe that's reason enough not to describe them that way.

One is a new collaboration between a cultic Los Angeles producer called Madlib and an even more cultic rap artist called Quasimoto - two proudly subterranean weirdo geniuses who are also, as it happens, the same person.

And then there's the thrilling new CD from Turf Talk, a hard-spitting rapper from Vallejo who takes no pride in his underground status. For him, the underground isn''t a place to live, it's a place to leave.

Ever since the late 1990's, Madlib has been at the center of his own hip-hop subculture, releasing a series of dusty and dazed singles and albums. (His long résumé includes the acclaimed 2004 album "Madvillainy," a collaboration with MF Doom.) Listening to his mellow, beat-driven collages is like spending time with a pothead record-shop owner who keeps remembering something funkier or weirder or funnier that he wants you to hear.

In 2000, Madlib released "The Unseen" (Stones Throw), a free-associative album credited to Quasimoto, an id with a sped-up voice who's interested in nothing you can''t spin or inhale. One track stopped halfway through so our hero could ask a clueless clerk, "Would you happen to have any, uh, Stanley Cowell, 1970's stuff?" Like his creator, Quasimoto is a record collector first, and everything else second.

Now comes the dizzying follow-up, "The Further Adventures of Lord Quas" (Stones Throw). It's even more disjointed and unpredictable than its predecessor, thanks in part to a series of Melvin Van Peebles samples. And throughout the album, Quasimoto delivers meter-busting lyrics full of inside jokes, nonsensical leaps. "Quasimoto, all around you like V.D.'s/Only the strong survive, so eat your Wheaties," he mumbles, apropos of nothing in particular, while riding a funk beat fit for a long-gone space age. While most rappers fight to hold your attention, Quasimoto can barely hold his own; he's always getting interrupted by skits and snippets, and he never seems to mind.

As you can imagine, Quasimoto isn''t the kind of hip-hop star who appears in big-budget music videos, although there is a great low-budget one, which he made himself. It's a clip for "Rappcats Pt. 3" (found at www.rappcats.com), a track that pays tribute to pioneering rappers, famous and otherwise. For the video, he has painstakingly assembled snippets and photographs of every single one. "I take it back like L.O.N.S./Remember Daddy Fresh?/Or Maestro Fresh Wes?" he rhymes, and the faces go flickering by.

Listen to enough of this stuff and you might start hearing hip-hop the way Madlib hears it: as a collection of scratchy old records to be bent and borrowed, tweaked and transformed. His world is a place where hip-hop is history, and he has attracted lots of listeners and critics who take that notion literally. To be a Quasimoto fan you don''t have to believe that mainstream hip-hop died in the early 1990's, but it certainly doesn''t hurt. His grubby underground lair is, for those who want one, a refuge from the shiny gansgta rap that continues to dominate the pop charts.

So where does that leave Turf Talk? Not (yet) popular enough to join the mainstream, not dissident enough to be adopted by the underground, rappers like Turf Talk exist in limbo. In the booming Bay Area hip-hop scene, Turf Talk is a rising rapper, the man behind the regional hits "It's ah Slumper" and "Sav Out." But Turf Talk's most recent CD, "Turf Talk Brings the Hood Colabilation" (Sick Wid It), has earned only a fraction of the critical attention paid to Quasimoto's latest.

Turf Talk's cousin and mentor is rap artist E-40, a Vallejo hip-hop pioneer who has spent more than a decade perfecting his own idiosyncratic version of California gangsta rap: his warp-speed rhymes are full of huge, distended vowels bounded by hyper-enunciated plosives. And on his 2004 debut album, "The Street Novelist," Turf Talk showed that he had developed his own version of the Vallejo sound.

He has a high, pinched voice, less cartoonish than his cousin's and more ferocious. When he snarled, "Cookin'' and cuttin'', dumpin'' and dumpin'' on one/Figure-eightin'' and skatin'' through intersections," the rat-a-tat syllables made their own sort of sense. Whereas Quasimoto drifts back in time, Turf Talk rushes furiously forward, propelled by gleaming digital beats.

Bay Area hip-hop is enjoying an unexpected boom. And so, faced with fierce competition from hungry veterans (like Keak da Sneak and Celly Cel) and even hungrier newcomers (like Federation and the Frontline), Turf Talk wasted no time: six months after his debut, he has returned with "Hood Colabilation," featuring an hour of crazed computer music and rowdy trash-talking.

Like many rappers from his part of California, Turf Talk often multitracks his vocals so he can echo himself, which makes his lyrics sound at once clearer and woozier: "Can''t rep nothing but the Vall-e-joe (Vall-e-joe!)/7-0-7, say it backwards, ho (say it backwards, ho!)." And in "Throw It in They Face Turf," he starts with a Q and A that Quasimoto might admire: "Why your face stay mugged up?/I''unno, prob''ly ''cause I''m intoxicated and all drugged up."

In magazines and newspapers, on blogs and message boards, "underground hip-hop" isn''t usually a neutral description but a self-selecting club - one that's closed to uncouth neighborhood hustlers like Turf Talk.

And Turf Talk himself probably doesn''t care: he's planning to come up from the basement as soon as possible, anyway. His cousin E-40 is to release his new album through Lil Jon's BME Recordings, and this fall Turf Talk plans to release his third CD, about a year after his first.

If Turf Talk succeeds, lots of people will wonder where on earth he came from. If he doesn''t, most will never know he existed. But whatever happens, when Turf Talk's journey toward the mainstream (however long or short) is over, here's hoping that someone like Madlib is still around, obsessing over a new generation of old pioneers. The least Turf Talk deserves is a loving and deeply idiosyncratic collector, ready to recycle his weird old records into weird new ones.