Ask the simple question to restaurants, food vendors and see how they react and what they say …

Starbird Chicken, Sunnyvale (14 Jun 2018)
Via email on their “contact us” page. Answered on June 19. Summary: from Northern California. Depending on availability they get it from Pitman’s (Mary’s), Petaluma Poultry, Zacky Farms or Foster Farms. Delivered fresh from processor near Modesto. At a minimum, all chicken is (non-GMO) veggie fed, USDA process verified, all natural, America Humane certified, no anti-biotics. Some is free range.

Chipotle Mexican Grill, Mountain View (16 Jun 2018)
Cashier didn’t know (and seemed surprised at the question) but got the manager. Manager had to double check and said the chicken comes from Arizona.

Puesto, Santa Clara (19 Jun 2018)
Waiter said he thought the chicken was local but that since it is a new restaurant they are still locating best sources for their meats. I asked him to check with his manager. Came back and said they get their chicken from Mary’s through Sysco.