Which terrain feature can be described as a linear geographic formation?

A spur is correctly identified as a linear geographic formation because it represents a ridge or hill that extends outwards from a parent mass of land, typically forming a prominent feature that protrudes in a linear fashion. This formation can often be identified on topographic maps, where it appears as a narrow extension or protrusion from elevated land.

In contrast, the other terrain features do not share the same linear characteristic. A valley is generally a low area between hills or mountains, often with a more U-shaped or V-shaped profile rather than a linear form. A hill is usually a rounded elevation without the extension element that defines spurs. A depression is simply a sunken area, which lacks any form of protrusion that would give it a linear attribute. Thus, the definition of a spur aligns perfectly with the characteristic of being a linear geographic formation, making it the correct answer.