Punk set out to overthrow the guitar hero decades ago, seeing long solos as pointless indulgences. It damaged the concept, but the species survives. Over the course of the day the gathered musicians used their electric guitars for tickle and twang, for keening and roaring, for funk rhythm and airborne melody, for conversation and competition.

Image Eric Clapton’s Crossroads Guitar Festival, at Toyota Park, outside Chicago, the third guitar marathon Mr. Clapton, left, has organized. Credit... Carlos Ortiz for The New York Times

Crossroads was a decidedly old-fashioned rock event. Every note, give or take an echo effect, was played by hand. And nearly every band welcomed guests during its set, implying that musicians can still reach back to a common foundation in the blues, even after decades of niche marketing and genre fragmentation. It wasn’t a blues festival — Chicago already has one — but largely a blues-rock festival, with Mr. Clapton, Mr. Beck, ZZ Top, Johnny Winter and Ron Wood of the Rolling Stones, who were once students and transformers of the blues, now appearing as forefathers.

Their elders and idols, like Mr. King and the 78-year-old Hubert Sumlin, Howlin’ Wolf’s longtime guitarist, played laconic, teasing, subtle solos. The blues-rockers were flashier and more brazen, qualities that long ago propelled their music into big rooms. The Robert Cray Band and Cesar Rojas and David Hidalgo of Los Lobos, showing just their bluesy side at Crossroads, soaked up blues-rock along with its blues sources when they got started in the 1970s and now sound rootsy themselves.

Funk rhythms, brittle and kinetic, are fully embraced by the youngest contingent, including Mr. Mayer, the gospel pedal steel guitarist Robert Randolph and the fierce Texas blues-rockers Doyle Bramhall II and Gary Clark Jr. Mr. Beck was up to date with them, leading a band with a thumb-popping funk bass player and using futuristic guitar-synthesizer tones in his solos, although the lessons of electric blues — the searing phrases, the tension in a melody line — have never left his playing. (He went back to unadorned blues in his spot with Mr. Clapton.)

For many of the musicians the concert’s historical sweet spot was the late 1960s and early 1970s. When not playing their own songs, they drew on Jimi Hendrix and Mr. Clapton himself. The Derek Trucks and Susan Tedeschi Band summoned the heaving, gospelly, two-drummer thrust of the Allman Brothers Band; Mr. Trucks and a guest guitarist, Warren Haynes, are both current members of the Allmans, who had to cancel their Crossroads appearance because Gregg Allman received a liver transplant last week.