What kind of damage can a gopher do to my plants and lawn in Riverside or Temecula, CA?

When I grew up in Murrieta and Temecula, CA we had gophers in our lawn – eating the lawn. Now that I have a property in Riverside I'm seeing gopher mounds in the neighbor's landscaping. I have a lawn, a few citrus trees and a flower bed. Should I be concerned about any of the plants in my yard? I mean, what do gophers eat anyway?