Which of the following is a key indicator that an area may contain UXO?

A key indicator that an area may contain unexploded ordnance (UXO) is historical military activity in the vicinity. Areas where military operations have taken place, such as training grounds, battlefields, or even near former military bases, are more likely to have remnants of munitions that were used but not detonated. This historical context provides a significant clue; when military forces have operated in a location, the chances of munitions, such as bombs, artillery shells, or other types of ordnance being left behind, increases substantially.

While other factors, such as residential development or active construction projects, may raise awareness of potential risks, they do not specifically indicate the previous use of munitions that would lead to the presence of UXO. Flora and fauna diversity typically relates more to ecological studies and conservation efforts rather than military history. Thus, understanding the history of military engagement is crucial in identifying potential UXO presence.