The Allman Brothers Band and RatDog will close out their joint summer run with one final show on Saturday at Red Rocks. Last night, on the penultimate evening of the tour at Charter One Pavilion in Chicago, the two groups continued their ongoing collaborations while some additional players shined as well. The ABB’s take on ‘It Hurts Me Too’ featured guest guitar from RatDog’s Mark Karan as well as bonus bass from longstanding Gov’t Mule associate Greg Rzab. After Karan and Rzab departed, Warren Haynes and Derek Trucks picked up acoustic guitars and were joined by Bob Weir on a similar instrument for a version of ‘I Shall Be Released.’ A bit later, Luther Dickinson, who is in the Midwest with the Black Crowes, emerged for the ‘One Way Out’ encore.