Edgar Rice Burroughs 
A Princess of Mars [EPUB ebook] 

John Carter, a Confederate veteran of the American Civil War, goes prospecting in Arizona immediately after the war’s end. Having struck a rich vein of gold, he runs afoul of the Apaches. While attempting to evade pursuit by hiding in a sacred cave, he is mysteriously transported to Mars, called Barsoom by its inhabitants. Carter finds that he has great strength and superhuman agility in this new environment as a result of its lesser gravity. He soon falls in with a nomadic tribe of Green Martians, or Tharks.