After having seen many pictures of the Lincoln Monument during his lifetime, Mr. Adams mistakenly recalled that he had actually visited the site. This best illustrates

This best illustrates source amnesia.

Explanation:

Source amnesia is a memory disorder that causes a person to remember a factual knowledge but also to distort contextual elements. The person has difficulty recalling where, when, or how they obtained such knowledge. This is related to a malfunctioning of explicit memory. In Mr. Adams's case, the distortion seems to be related as to how he obtained that knowledge. He can remember the monument, but not that he saw it through pictures. He thinks visiting the monument is how he formed that memory.