Final answer:
The source of the allusion in the sentence is literature, with the mention of sandy white beaches and turquoise waters representing an idyllic place resembling a utopia.
Step-by-step explanation:
The source of the allusion in the sentence is literature. The mention of sandy white beaches and turquoise waters evokes the idea of an idyllic place, resembling a utopia. This is a common allusion found in literature, where authors often use the imagery of beautiful beaches and clear waters to symbolize paradise or a perfect place. By describing the Gulf of Mexico location as its own little utopia, the sentence creates a reference to this literary motif.