Answer:
If my aunt were not in Dismount Fort, I might have forgotten that small town where I went to elementary school only for two years in the late 1960s.
Step-by-step explanation:
An adjective clause is a group of words with at least a verb and a subject that does not express a complete thought (they're dependent clauses) and whose function is to modify nouns; These type of clauses usually begin with a relative pronoun (who, whom, whose, that, which) or a relative adverb (when, where, why).
So, in the sentence selected, the adjective clause is "where I went to elementary school only for two years in the late 1960s" because it is a dependent clause (it does not express a complete thought on its own), it modifies or describes the noun phrase "that small town" and it begins with the relative adverb "when."