For a couple of laid-back surfers, Ben Harper and Jack Johnson really know how to get a crowd worked up.

Currently in the midst of their summer-long U.S. tour, Ben Harper and his band, The Innocent Criminals, have gradually built a strong following through their impassioned live performances, converting a few more fans with every stop.

Although it was pouring rain outside, you wouldn’t know it from the relaxed, beachy atmosphere inside Hilton Coliseum Saturday night.

Johnson, the opening act, played to a backdrop of palm tree silhouettes, the warm hues of the orange and purple lights perfectly providing a visual complement to his summery, acoustic-groove oriented songs. The more free-spirited individuals in the crowd took the opportunity to dance, and although Johnson’s set lacked variety, the musician/surfer/filmmaker came across as genuine.

Swaying back and forth while delivering his low, humble brand of vocals, Johnson won the crowd over with songs from his new album “On and On,” as well as 2001’s “Brushfire Fairytales.” Even the most indifferent, jaded cynic in the crowd couldn’t help but sing along to the infectious chorus of “Bubbletoes.”

Harper’s enthralling performance never gave the crowd a chance to lose interest. Drawing inspiration from musical kindred spirits Jimi Hendrix, Marvin Gaye and Bob Marley, Harper flowed effortlessly between genres while never seeming out of his element.

From his Marley-esque reggae anthem “With My Own Two Hands” to his lusty rendition of Marvin Gaye’s “Sexual Healing,” Harper wore his influences on his sleeve while still managing to carve out a distinct musical niche for himself, making it clear why he has such a devoted following.

Harper also showed musical versatility throughout the night, picking up and playing a wide variety of instruments. Even while sitting down, he commanded the attention of every pair of eyes in the coliseum as he played his trademark slide guitar, seeming to channel his soul directly through the horizontal instrument.

But as captivating a solo performer as Harper is, the unique contributions of each of the five Innocent Criminals made Saturday’s show what it was. From the funky bass lines of the mountainous, charismatic Juan Nelson to the sparkplug percussion of Leon Mobley, each musician added a different spice to the flavorful concoction that is Ben Harper and The Innocent Criminals.

The musical vibe was so contagious it prompted one fan to find her way on-stage and shake her booty with the band. Although security made a feeble attempt to remove her, it was clear she was welcome on-stage by getting down with Nelson and Mobley before diving back into the audience.

“That girl’s got guts,” said an obviously impressed Harper.

The crowd sang along fervently to “Burn One Down,” which featured the zealous hand-drumming of percussionist Mobley in the forefront. The popular pot-anthem eventually dissolved into an extended solo for Mobley as Harper challenged the crowd to a few rounds of vocal call-and-repeat, where the engrossed Ames audience did exceptionally well.

Before calling it a night, Harper came back for an encore, treating the enamored audience to a couple of intimate acoustical pieces before bringing buddy Jack Johnson on-stage for the duet “By Your Side.”

Overall, the night was an adventure through many genres and styles, and although this may not be the biggest tour of the summer in terms of numbers, it is undoubtedly one of the most diverse and musically rewarding.