drip line

a small but distinct linear pattern in the soil that forms when rainwater is focused to drip in certain places; they are an example of a disturbance process

A tree with a dense crown of leaves can have a drip line around its outer extent. The edge of the roof of a rock shelter can produce a drip line. Likewise, the edge of a roof can produce a drip line, if there’s nothing to divert the rainwater (e.g., a gutter).