The Forest Grass Mouse lives in a small area of the mountains of northwestern Argentina. Its back is olive-brown, and it occurs in Yungas forest and high-elevation grasslands.
It is medium-sized, with a head-and-body length of 151–203 mm. Its back is uniformly olive-brown, finely streaked with black hairs. The underside is not strongly contrasting, and the underside of the tail is slightly paler.
It lives in Yungas forests and high-elevation grasslands, as well as grasslands in the Chaco region. Breeding activity begins in early spring; individuals caught in June were reproductively inactive. Many individuals trapped in grasslands from June to October were molting.
An extinction-risk assessment has not been added yet.