Columbus presented his original ship's log to the Spanish sovereigns at Barcelona upon his return in 1493. Queen Isabella ordered a copy made. The original disappeared. The copy - the so-called Barcelona copy - passed to Columbus at the start of his second voyage and remained with his family after his death in 1506. Sometime in the 1540s, the monk Bartolome de las Casas obtained the Barcelona copy and made an abstract now called the Diario, writing most of it in his own third person but preserving long passages in Columbus's own words, particularly the sections describing his movements through the Bahamas. The Barcelona copy itself vanished late in the sixteenth century. Las Casas's Diario was rediscovered in 1795 and published thirty years later. Every theory about where Columbus landed depends on this chain of copies - an original no one has seen, transcribed by a monk working from a copy made for a queen, recovered two centuries after it was written.

At least ten Bahamian islands have been proposed as the real Guanahani. San Salvador Island, formerly called Watlings Island, has held the title since 1925, when it was officially renamed based on the identification first proposed by Juan Bautista Munoz in 1793. The influential historian Samuel Eliot Morison endorsed it in 1942, and it remains the most widely accepted candidate. But Samana Cay gained prominence after a 1986 National Geographic feature revived an 1880 theory by U.S. Navy captain Gustavus Fox. The Plana Cays entered the competition in 1974 and gained a forceful advocate in researcher Keith Pickering, who argues they have "fewer and less serious problems than any of the others." Grand Turk Island was proposed as early as 1825. Cat Island held the lead through much of the eighteenth century before falling from favor. Mayaguana, Conception Island, East Caicos, Egg Island, and Lignum Vitae Cay round out the field. Each theory has its partisans, its scholarly papers, its moment of ascendancy.

Historians have used two main methods to locate Guanahani. The first traces Columbus's transatlantic route using the distances and directions recorded in the Diario, adjusted for the uncertain length of his league, the unknown speed of ocean currents in 1492, and the magnetic declination of his compass - which pointed somewhere other than true north, by an amount no one can determine precisely. Different assumptions about these variables send the endpoint to different islands. John McElroy's 1941 attempt landed near Watlings Island after applying a correction factor. Luis Marden's 1986 analysis favored Samana Cay. Keith Pickering's 2004 work using updated magnetic data pointed to the Plana Cays.

The second method follows Columbus's island-hopping track from his first landfall through the Bahamas to Cuba. The Diario describes courses, distances, coastline shapes, and harbors in enough detail to build an itinerary - but the log also contradicts itself in places. Columbus describes four coastlines at his Island III that fit Long Island almost perfectly, yet his distances and directions between islands produce tracks that no single starting point resolves without strain.

Columbus left a description that is both vivid and maddeningly vague. Guanahani was flat, green, bean-shaped, surrounded by a reef with a harbor "large enough to store all ships of Christendom" between reef and shore. It had muchas aguas - many waters - and a large laguna in the middle, a word that could mean either lagoon or pond. Most candidate islands have one or the other. On October 14, Columbus explored "the other part, which was the eastern part" by boat rather than on foot, which may or may not mean Guanahani consisted of more than one island. Juan de la Cosa's map of 1500, drawn by a man who sailed with Columbus, shows Guanahani as what appears to be a cluster of small islets rather than a single landmass. Columbus also saw a flickering light the evening before landing, roughly 35 miles from where he came ashore - meaning the light came from a different island entirely, narrowing the possibilities differently depending on which island you begin with.

Columbus mentioned Guanahani only once in the letter he wrote to his patron Luis de Santangel upon returning to Spain in 1493. That single mention, in a letter printed widely and translated across Europe, was enough to make the name famous. The Taino people who gave the island its name did not survive to see the debate. Within decades of contact, their population across the Caribbean collapsed from disease, forced labor, and violence. The name Guanahani endured because a sailor wrote it down and a printer set it in type. Five centuries later, scholars still argue over which dot of coral and sand it belonged to. The island itself - whichever one it is - remains flat, green, and ringed by reef, much as Columbus described it. The mystery persists not because the evidence is missing, but because what survives points in too many directions at once.