Is it a gopher or something else? How do I find out?

Something is digging around the periphery of my patio where the lawn starts. There is soft dirt dug up and there are some other areas where I see fresh digging. It seems like some critter has been digging a tunnel. How do I find out what it is and how do I get rid of it? I have recently planted a vegetable patch with beautiful heirloom tomatoes which are thriving, and a lot of beautiful lettuce, chard, strawberries, cucumbers etc. It would be terrible to lose it all. HELP!!!