County fairs are a marvel of American music, from local blues bands playing for free to heavy metal blasting from rides to ambient midway organ tunes. More historically important than carnival noise, however, is the rich thematic source material that rural and local fairs provide to a huge vein of American music.

It's no surprise that pop music about fairs is the province of roots and folk/blues-based rock, while urban forms like hip-hop, jazz and techno make only scant references. But even in the rock and R&B tradition, the depth of fair music varies. Some music touches the fair in name only, like the Replacements' alt-hit "Merry Go Round," the Ohio Players' funk smash "Love Rollercoaster," the Stooges' proto-punk disc Funhouse or the fine 2007 disc Journal by Midwestern country-rockers Booker Lee and the County Fair.

Real fair music begins with luscious, familiar, sensory details. Amusement park sensations provided favorite details for early rock/soul acts. Freddie "Boom Boom" Cannon rode the merry-go-round, the Ferris wheel and the tunnel of love at "Palisades Park"; the Drifters could "almost taste the hot dogs and french fries they sell" when they were "Under the Boardwalk"; and Brian Wilson lost his girl when he couldn't win a stuffed bear at the Beach Boys' "County Fair." This descriptive mode continued on the title track to Phil Alvin's 1994 disc County Fair 2000, where the rockabilly master inhales cotton candy, a candied apple, pink lemonade and a mustard dog.

Deeper in the fair-based music tradition, beloved sight and smell details give way to a murky, slippery sense of impermanence. Leon Russell's 1975 disc Carney isn't about carnivals, but rather references carnival themes to create a sense of doubt and unease. Marin rockers Protein joke in their 1997 song "Obligations" that age has made them forgetful, but highlight the memory that "we used to all be at the county fair / With feathered hair" as a moment of clarity. In Joe Walsh's proggy-druggy classic rock cut "County Fair," he observes that "it's a county fair picture / Part of me's there," seeing that "some of the pieces are still at the fair."

The deepest core of fair music gets it both ways, as if the very immediacy of comfortable, fleeting pleasure is a signal for dread. Something on John Wesley Harding's 2004 cut "The Night He Took Her to the Fairgrounds" is mysteriously wrong, and it's not just broken hearts on the midway. Graham Parker's 2004 track "Fairground" describes fair workers with both desire and cynicism. Parker doubts his own hopes ("Get your tight blue jeans out / And try to get them on"), wants to ask a fair worker how he feels, and wonders if a young carney "murdered that clown / and got away scot-free."

The supreme achievement in American fair music is Bruce Springsteen's "County Fair," an outtake from his early '80s Nebraska era. Here, the gooey thrills of Freddie Cannon and the Drifters merge with the darker dissatisfaction of Walsh, Protein and Parker. Springsteen is conscious enough of fair impermanence to name the free local band James Young and the Immortal Ones. As he watches fellow fairgoers stuck in traffic, he looks heavenward, and with an ominous, communal minor chord, prays that "I never have to let this moment go."

Finally, the fair-music genre is graced by Elvis Presley, with "The Fair Is Moving On" from his gospel/big-band, late-'60s "mature" period. If the Boss' "County Fair" is a triumph of classic art, the King's "The Fair Is Moving On" is better yet a triumph of plain-spoken fair music. The song begins with Presley matter-of-factly noting that "All the rides are over and done . . . and no prizes are left to be won." It seems like an obvious thrill when he later sings "the trailers will soon hit the road." But the thrill isn't really gone; "It's the last time you'll be on your own," Presley sings, tempting the audience to await the return of next summer's county fair.

The Sonoma County Fair runs now through Sunday, July 29, with plenty of live music. Free concerts include: July 18 at 8pm, Eddie Money; July 19 at 7pm, Jonas Brothers; July 23 at 8pm, Kimberley Locke; July 24 at 7pm, Pride and Joy; July 25 at 8, Blake Shelton; July 26 at 8, Melissa Manchester; July 27 at 7, batalla de grupos; July 28, 2pm to 9pm, blues festival with David Jacobs-Strain, Volker Strifler Band, Patrick Sweany, Michael Burks, Janiva Magness and John Lee Hooker Jr.; July 29 at 4pm, Mariachi Los Camperos. Sonoma County Fairgrounds, 1350 Bennett Valley Road, Santa Rosa. $7; kids under 12, free; Monday, carnival rides, $1; Tuesday before 3pm, everyone free; Tuesday and Thursday, $20 for all rides; Wednesday, seniors free. 707.545.4200. www.sonomacountyfair.com.

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