Golden illusion; a land or means of unbounded wealth. Orellana, lieutenant of Pizarro, pretended he had discovered a land of gold ( el dorado) between the rivers Orinoco and Amazon, in South America. Sir Walter Raleigh twice visited Guiana as the spot indicated, and published a highly-coloured account of its enormous wealth. Figuratively, a source of wit, wealth, or abundance of any kind.
The real “land of gold” is California, and not Guiana. (See Balnibarbi.)
“The whole comedy is a sort of El Dorado of wit.” —T. Moore
El Dorado (masculine), “the gilt one,” can hardly refer to a country; it seems more likely to refer to some prince; and we are told of a prince in South America who was every day powdered with gold-dust blown through a reed. If this is admitted, no wonder those who sought a golden country were disappointed.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894