Hi Lori,

It's tough to say for sure from the photograph, but it resembles Epipactis helleborine, also known as garden helleborine.  It's a plant of European origin that has shown up in the Denver metro area as a weed of disturbed places, lawns, and gardens.  

Have you ever seen it in flower?  Helleborine is in the orchid family, and has characteristic orchid flowers that could confirm its identity.  Helleborine can regenerate from roots, but pulling it thoroughly can work to control it, as can cutting it at the soil surface repeatedly (which will starve the plant over time).  

I hope this is helpful!

Cordially,

John