If there were ever any doubt about who Taylor Swift's fan base is, one look around jam-packed Minute Maid Park Saturday night confirms how she made $45 million last year (according to Forbes magazine).

Pre-teen and teenage girls are everywhere — in homemade T-shirts emblazoned with the singer's name and her favorite number, 13, carrying handmade signs (which are confiscated at the entrance by overcautious security personnel) and singing every word of the singer's songs about mean girls and bad boyfriends at the top of their lungs.

Before the concert begins, they stand in long lines (usually with Mom but sometimes with Dad) to have their makeup done by CoverGirl representatives (Swift has a lucrative deal with the cosmetics giant), buy T-shirts and wait to use the women's restrooms. (The concert is so female-dominated that the men's rooms go virtually unused the entire evening.)

By the time Swift's thrill-packed two-and-a-half hour concert ends around 11 p.m. — after nine costume changes and just as many different guitars, an encore where the singer floats over the audience in a flying balcony amid silver confetti like Glenda the Good Witch in The Wizard of Oz, and a surprise appearance by Nelly — many of the younger girls are asleep in their parent's arms. But ask them today and they'll have memories of Swift that will likely last a lifetime.

No matter how rabid her adolescent fan base is, it takes more than screaming girls for the 21-year-old singer to rise above the level of a Disney-singer-of-the-moment into a bonafide superstar who has sold more than 20 million albums and 25 million digital tracks in the past five years, and whose new album,Speak Now, sold more than a million copies in its first week of release.

In the concert at Minute Maid Park, which attracted a sellout crowd of 42,000 and was the last stadium stop on her "Speak Now" world tour, she leaves several clues as to why she is so popular.

She exudes sincerity

Even though her show seems highly scripted, Swift manages to look like she truly is overwhelmed by the adulation. There's an intimacy that appears genuine, unless she's a really good actress. (If that's the case, she deserves an Oscar.)

Swift first appears on stage in a sparkly gold fringe dress and black boots — her porcelain skin and deep red lips magnified on two jumbo screens — with a look of wonder and amazement on her face. "Hello, Houston, Texas, I'm Taylor," she introduces herself in an aw-shucks kind-of-way, before launching into "Sparks Fly," from her new album.

Although one can imagine she said pretty much the same thing in a Lexington, Ky., show a week earlier (where the set list was virtually the same), she looks genuinely awed by her surroundings and thankful to be on stage.

Throughout the evening, she exudes a "pinch-me, I must-be-dreaming" attitude that is disarming. "It's Saturday night in Houston, Texas and you could be anywhere in the world. I thank you from the bottom of my heart for hanging out with me," she says, as the crowd roars.

With 17 songs and three encores, the show seems overly long at times, particularly during segments where dancers mindlessly perform on stage as Swift catches her breath offstage. And there's a segment where she walks the floor of the baseball stadium shaking hands with fans that seems like it will never end. But no one can complain that Swift hasn't given them their money's worth.

She knows how to write songs

While her singing is shaky at times (such songs as "The Story of Us" and "Long Live" don't sound nearly as polished live as they do on her CDs), Swift is a masterful songwriter, with sophisticated ruminations on teenage heartbreak. "My songs are mostly about loves and breakups because that's something I think about the most," she says at one point in the concert. "I'm a hopeless romantic."

Called the "poet laureate of puberty" by the Washington Post, she confirms the assessment, introducing the song, "Fearless," by telling the crowd to think about "when you've come home from the best first date in your life and you're so happy that you feel maybe fearless." It's a sentiment that anyone of any age can relate to.

One of the show's best segments comes when Swift moves to another set in the massive stadium, located closer to home plate than to the outfield (where much of the show takes place on a gigantic, multi-level, red-curtained stage). The second setting, which consists of a fake palm tree on a small island, has a more personal feeling as Swift sings "Fearless" and several other songs, including "Last Kiss," "Never Grow Up," and the beginning of "You Belong With Me," while playing the guitar or ukelele.

Stripped of the bombastic production numbers, with only her voice and guitar, she creates an intimate bond with the massive audience that says more about her success than anything else all evening.

In an extensive recent profile in New Yorker magazine, Swift says her career role models are singer-songwriters Bruce Springsteen, Kris Kristofferson and Emmy Lou Harris because "they've evolved but they've never abandoned their fans." One can imagine Swift's career taking that trajectory as she grows older.

She's pretty but approachable

Tall and a bit gangly, with crimped hair and porcelain skin, Swift has the looks of a 1930s movie star. When her face is flashed on the giant screens, one can imagine her as a silent movie star in another era. She's beautiful, but not so gorgeous as to be threatening.

During the show, she shows many moods, from prim-and-proper in a lace dress and braided hair while singing "The Story of Us" to modern-girl-with-a-fighting-spirit in a 40s-style purple sun dress and lace gloves in an extended fantasy sequence where she disrupts a wedding and runs away with the groom, while singing "Speak Now."

No matter what her persona is, she's always the girl in class who may not be the most popular, but the one you want to hang out with.

She's a role model

Though only 21, there's a bit of an "old soul" about Swift. She doesn't drink or smoke, hasn't had any brush with the law, like Lindsay Lohan, or a trip to rehab, like Demi Lovato, and seems much wiser than her years.

She even writes thank you notes.

But she doesn't come across as a goody two-shoes. While she doesn't have a permanent tattoo, in concert her lucky number, 13, is scribbled on her right hand and the Joni Mitchell lyric, "It's love's illusions I recall. I really don't know at all," runs along the length of her left arm.

It may be a tricky time professionally as Swift grows into adulthood, but she seems poised to make the transition by bringing her audience along with her on her journey.

She has a bond with her fans and her family

Before the show, Swift's mother and manager, Andrea, roams the stadium for fans and brings them up to the pit near the stage to be near the action during the concert. It adds an intimacy to the massive stadium concert and gives young girls the experience of a lifetime.

While Swift now lives in her own Nashville apartment, she retains a tight bond with her family. And she explains her Bayou City ties, telling the crowd that her mom is a Memorial High School graduate and that her aunt, Alison, lives in Houston.

She knows how to have fun

While her teen angst songs draw big sing-alongs throughout the evening, Swift seems to have the most fun when Nelly makes a surprise appearance and they launch into a sizzling duet of "Just A Dream." For a few moments, Swift transforms from teen queen to a girl just having fun.

She becomes a rapper, singing the lyrics in staccato fashion, and dances in a non-choreographed moment like a girl at a slumber party with friends. It's charming moment — and the evening's most revealing.