The coevolution of the two organisms has never been investigated but, given the ancient lineage of mountain beaver, may provide some interesting insights. Mountain beaver are strict herbivores. They are known to eat a wide range of plant species, which often includes just about all species within reach of the burrows. Herbaceous plants are eaten whole while woody plants are discarded after the bark has been peeled off for food. Clipped vegetation can often be observed near burrow systems.
Mountain beaver are voracious eaters.
Studies have shown that the majority of their active time is spent gathering, handling and eating food. They seldom venture far from their burrows, which may open directly into suitable vegetative stands. The animals forage for short distances above ground, then carry or drag the cut vegetation, which may vary in length from a few inches to several feet, to the burrow. There the material is cut into short sections at the burrow entrance and carried into the burrow to be eaten or stored. Animals may eat vegetation outside of the burrow, but most often consume it in feeding chambers which are adjacent to the nest.