Which feature would suggest the presence of glacial activity in a region?

The presence of boulders scattered on the surface is indicative of glacial activity in a region. This feature is a result of processes known as glacial erratics, where boulders are transported by glaciers and deposited as the ice melts. These boulders can vary in size and composition, often differing from the surrounding rock, as they may have originated from distant locations. The distribution of these erratics provides evidence of past glacial movements and the extent of glaciation in the area.

In contrast, deep soils are generally associated with longer periods of weathering and soil formation, which might not correlate with frequently disturbed landscapes like those found under glacial influence. Flat river valleys, while they can be shaped by glacial activity, can also result from various geological processes unrelated to glaciers. Lush vegetation is typically characteristic of a stable ecosystem, which does not directly indicate past glacial activity. Thus, the scattering of boulders is the most telling sign of ice-related geological history.