Why did magellan give an area of argentina the name patagonia?

Hey There!

The name Patagonia comes from the word patagón, which was used by Magellan in 1520 to describe the Indians of the region, whom his expedition thought to be giants. It is now believed that the people he called the Patagons were Tehuelches, who tended to be taller than Europeans of the time.

The Argentine researcher Miguel Doura observed that the name Patagonia possibly derives from the ancient Greek region of modern Turkey called Paflagonia, possible home of the patagon personage in the chivalric romances Primaleon printed in 1512, ten years before Magellan arrived in these southern lands. The hypothesis was accepted and published in a 2011 New Review of Spanish Philology report. 

the answer to your question is a. the salt plains

in 1811, he led an expedition, known as the george c. sibley expedition, to improve relations with the pawnee and kansa tribes, and also to locate the rumored jefferson's salt mountain