Each zone in the California Roseville Mission covers a different stake within the mission. Thus, the Gridley Stake is also the Gridley Zone, The Redding Stake is also the Redding Zone, etc. Each zone has within it several districts, composed of different wards.
This is the official map which all new missionaries receive in their mission packets
This is the unofficial map, with more cities listed and a higher resolution.
"Invite others to come unto Christ by helping them receive the restored gospel through faith in Jesus Christ and His Atonement, repentance, baptism, receiving the gift of the Holy Ghost, and enduring to the end." - Preach My Gospel D&C 50:14