Over the weekend, RatDog and Gov’t Mule opened what promises to be one of the summer’s most collaborative co-headlining tours. On Friday the two groups appeared at Eugene, OR’s Cuthbert Amphitheatre, and Warren Haynes kicked things off by joining RatDog on ‘Masters of War,’ ‘West L.A. Fadeaway’ and ‘Iko Iko’ halfway through the group’s set. The tour continued the following night at Seattle’s WaMu Theater, where RatDog keyboardist Jeff Chimenti keyboardist Jeff Chimenti sat in with Mule on ‘Sugaree,’ while saxophonist Kenny Brooks joined the quartet for ’30/20 Blues.’ The members of Gov’t Mule then returned the favor during RatDog’s show-closing set, with Danny Louis playing keyboards on ‘Little Red Rooster’ and Haynes adding guitar to ‘Bird Song.’ This evening both bands will appear at Boise, ID’s Idaho Botanical Garden.