This is a Phase III, multicenter, open-label, three-arm, randomized study in participants with unresectable locally advanced or metastatic colorectal cancer (CRC) who have received at least two prior regimens of cytotoxic chemotherapy for metastatic disease. The study compares regorafenib, a standard of care therapy in this setting, to cobimetinib plus atezolizumab and atezolizumab monotherapy.