First, you need to identify whether you have pocket gophers or voles. I am including the URL to information to help you identify the rodent you have. I am also including the URL to each rodent that has information on control or management ideas.
Pocket gophers build a mound of dirt but there is no open hole to the tunnel. Voles have a open hole to the tunnel but may or may not build a mound of dirt.
http://extension.colostate.edu/topic-areas/natural-resources/burrowing-animals-determining-species-by-burrows-damage-6-521/ (Burrowing Rodent ID)

http://extension.colostate.edu/docs/pubs/natres/06515.pdf (Pocket Gophers)

https://extension.colostate.edu/topic-areas/natural-resources/managing-voles-in-colorado-6-507/ (Voles)

Best,
Marvin