In 1539, the Spanish explorer Ulloa reached the mouth of the Colorado River without knowing of the river`s existence. The actual discovery of the river`s mouth was made by Alarcon in 1540. Getting past the tidal bore, he proceeded upstream in boats pulled by ropes to a point near Lighthouse Rock. Two officers in Coronado`s expedition, Diaz and Cardenas, also reached the Colorado and Cardenas discovered the Grand Canyon.
During the 1770`s, Franciscans named the river "Colorado" on account of its red tinge during the spring melt off. General William Henry Ashley, descended the canyons of the Green River in 1825 and provided information about the upper Colorado.
With the establishment of a military post at the mouth of the Gila River for the protection of gold miners bound for the fields of California, the U.S. government grew more interested in the Colorado. Topographical engineers from the War Department explored the river and two expeditions by Major J.W. Powell in 1869 and 1871-72 provided detailed information.
The Colorado River`s hydroelectric power was harnessed by the building of the Hoover Dam during the Great Depression. Agreements have provided for the removal of so much of the water flow for irrigation and municipal purposes that the river, described in 1539 as running "with so great a rage into the land that it was a thing to be marvelled at," is now a comparative trickle.