Melchior Diaz

1540: Colorado River delta first explored by Spanish explorer Melchior Diaz. He journeyed up the mouth of a river now known as the Colorado from the gulf and sends expeditions from the river to present day Imperial Valley.

His party made the first European crossing of the Colorado River, near Yuma, ARIZONA. They discovered and reported geothermal hotsprings, probably the ones near Calexico, Mexico.