Step-by-step explanation:
The word "desideratum" is a noun that refers to something that is desired or wanted. It represents a goal, an objective, or a thing that someone is seeking or aiming to achieve. In the given context, when the speaker says, "Those mountains heralded the approach of my desideratum," they are suggesting that the mountains are a sign or indication that they are getting closer to something they have been desiring or wanting. The mention of Alaska indicates that Alaska is the desired destination or objective the speaker has been anticipating.