Two of the 1970s most popular bands, Chicago and the Doobie Brothers, will partner for their annual summer tour of amphitheatres beginning July 11.

The 21-date summer tour will kick off at the Anselmo Valencia Amphitheatre in Tucson and run through August 24′s show in Scranton, PA. The bands will zig-zag their way across the country over the course of the six-week excursion, picking up dates that include Denver, Atlanta and Boston along the way.

The Doobie Brothers, with original members Tom Johnston and Pat Simmons and 30-year veteran John McFee, are celebrating their 40th anniversary with a number of benchmark events. The band’s recent tour of New Zealand yielded sales of over 40,000 tickets (nearly 1 percent of the country’s population).

Four founding members of Chicago – Bobby Lamm, Lee Loughnane, James Pankow and Walt Parazider – will be on hand for this summer’s tour. The band will continue its popular “Sing With Chicago” program, a fundraiser that has already yielded over $130,000 for the American Cancer Society. Fans in each city where the band will appear can bid on a ticket package that includes the opportunity to appear onstage with the band when they perform “If You Leave Me Now.”

Chicago and Doobie Brothers tour dates, summer 2012:

Ticket information is available on the Chicago and Doobie Brothers websites.

- Michael Verity, CBS Local