Most of the classic rockers at this weekend fest have toured the area extensively in recent years, but there’s something intriguing about seeing them all together outdoors — a sort of midlife-crisis Woodstock in the Mojave. What makes Desert Trip especially interesting is the possibility of these British and American musicians interacting onstage. Saturday’s headliners, Paul McCartney and Neil Young, have jammed on “A Day in the Life” and “Only Love Can Break Your Heart” at each other’s gigs. Friday’s assigned roommates, The Rolling Stones and Bob Dylan, have shared guitarists (Mick Taylor) and covered each other’s tunes live (“Like a Rolling Stone” and “Brown Sugar,” respectively). The Who also have remade songs by the Stones and lyrically tipped their hat to Dylan. While only Young, Dylan and McCartney continue to write compelling new material, the foreboding presence of the relatively reclusive Roger Waters raises expectations for Sunday’s finale. Also Saturday-Sunday, Oct. 8-9, and Friday-Sunday, Oct. 14-16.