That is what we discovered on Wikipedia concerning the Gully Days:

A gully is a landform created by running water, mass movement, or both, which erodes soil to a sharp angle, typically on a hillside or in river floodplains or terraces.

Gullies resemble large ditches or small valleys, but are metres to tens of metres in depth and width, are characterized by a distinct 'headscarp' or 'headwall' and progress by headward (i.e., upstream) erosion. Gullies are commonly related to intermittent or ephemeral water flow, usually associated with localised intense or protracted rainfall events or snowmelt.

Gullies can be formed and accelerated by cultivation practices on hillslopes (often gentle gradients) in farmland, and they can develop rapidly in rangelands from existing natural erosion forms subject to vegetative cover removal and livestock activity.