I hate to burst your bubble but this image is overflowing with logical fallacies.
Case in point: these ruins were supposedly installed during Spanish colonisation of the island, meaning they are at least
400 year old.
Now take a look at this environments vegetation -
In temperate deciduous forests a thick bark helps to limit moisture evaporation from the tree's trunk, but as you can see, the trees here have a thin and smooth bark surface, implying that the humidity of the surrounding air must be quite significant in order to reduce the need for overt moisture-retaining adaptations.
This tree bark has clearly evolved in a continuously humid atmosphere, the only places on earth having such a climate being the tropics, between the Tropic of Cancer at approximately 23°30' (23.5°) N latitude, and the Tropic of Capricorn in the southern hemisphere at 23°30' (23.5°) S latitude.
Putting the island within this area -
The only part of this region that fits the bill as being susceptable to Spanish colonisation is therefore one of the outlying islands along the coast of northern South America or Central America and perhaps the Carribean.
As this TRaP satellite data shows, every year, very high quantities of rain are present across the entire landmass of this area -
Right then, take a look at that first pic at the beginning of the post. Toward the bottom of the screen you will see a metallic grill. The only metal economically feasible and available to Spanish technology at the time would have been iron, therefore we can safely assume that that metal is indeed, Fe.
Rust is the oxide that is formed by open-air oxidation of iron. The chemical composition of rust is mainly iron(III) oxide (Fe2O3), and under wet conditions may include iron(III) oxide-hydroxide (FeO(OH)).
Also, consider that this island must be relatively small to fit narrative purposes, and therefore, regardless of the location of this iron on the island, significant wind-carried water particles from the surrounding ocean, SALT WATER PARTICLES
, will periodically come into contact with the surface of the iron.
Salt water speeds up the rusting process, and combined with 400 years of intense rainfall, one can assume that perhaps 3 or 4cm of iron by this time will have been oxidised to the structurally weak iron(III) oxide and even iron(III) oxide-hydroxide.
Such heavily oxidsed iron would be so fragile and flakey, it would have literally been blown or eroded away by now. Only small stubs would be left of any such structure installed by Spanish colonialists.
Therefore we can surmise one thing, either Naughty Dog has completely dropped the ball on this, shattering the 4th wall, or someone else has been building on the island since the Spanish - approximately within the last 50 years...