Which feature would be represented by closely packed contour lines on a map?

Closely packed contour lines on a map indicate a steep slope. Contour lines represent elevation on a topographic map, and when they are densely arranged, it shows that there is a rapid change in elevation over a short horizontal distance. This means that the terrain is steep; as you move along the ground, the elevation is increasing or decreasing sharply.

In contrast, a gradual slope would have contour lines that are spaced further apart, indicating that the elevation changes more slowly over distance. A flat area would have contour lines that are either very widely spaced or nonexistent, as there is little to no change in elevation. A river valley would typically show contour lines that follow the shape of the valley, often spaced closer together on the sides but not necessarily indicating a steep slope unless they are very tightly packed, which is not a defining characteristic of valleys. Thus, the correct choice clearly illustrates the relationship between contour line spacing and slope steepness.