Thank you for the image as it clearly shows the important identification marks.
The caterpillars are the large yellow underwing, Noctua pronuba, an insect which was first noticed in Oregon during the early 2000s. They feed on plants at night, during the cool season, whenever the night-time temperatures are above 40 F. Thus, they are sometimes referred to as winter cutworms.
Since then, they have been important pests of lawns, vegetables, and many ornamental plants.
General management for caterpillars in home gardens relies on several strategies: Handpick the caterpillars; feed them to the chickens; destroy the pupae (resting stage; see page 3 in the link below) found while working the soil in the spring; or use Bt (Bacillus thuringiensis). Unfortunately, Bt is effective only when the caterpillars are less than half-grown. Those in your hand will be unaffected.
The “Large Yellow Underwing, A New Cutworm in Idaho” contains a detailed description of these sometimes voracious caterpillars, as well several images of their activities in Idaho’s agricultural fields shortly after they arrived. http://www.cals.uidaho.edu/edcomm/pdf/CIS/CIS1172.pdf.