military supplies had to be transported across the desert more than two hundred miles, in summer temperatures well above 100°. This was a new task for the United States Army. Even before Major Heintzelman's detachment was sent to Yuma, the War Department had considered establishing a water route to and up the Colorado River. At the same time that Major Heintzelman and his detachment left overland for Fort Yuma, Lieutenant George Horatio Derby was ordered to proceed by boat to the mouth of the Colorado in order to map all points important for its navigation. The object of the expedition was to "open a route of transportation by water to the mouth of the Gila, for the supply of the post to be established there."7
Derby was assigned to the 120-ton schooner Invincible ^ Capt. Alfred H. Wilcox, with a crew of thirteen. He left San Francisco on November i and sighted the mouth of the river on December 23, 1850. Proceeding upstream, he took soundings and charted the river for a distance of thirty miles before he was forced to anchor. An Indian was sent overland to Camp Independence with a note announcing the arrival of the party, whereupon Major Heintzelman left the fort with five men, reaching the Invincible on January 14. The army supplies were unloaded at Howard's Point on the Sonora bank and hauled overland by wagon to Camp Independence. After completing his survey of the river. Lieutenant Derby made the following report to the War Department:
... I have no hesitation in saying that it [the Colorado] may be navigated at any season of the year by a steamboat of eighteen or twenty feet beam, drawing two and a half to three feet water. A small stern-wheel boat, with a powerful engine and thick bottom,
I would respectfully suggest to be a proper . . . vessel for this navigation At the present
season (January, February and March) supplies from vessels arriving from the gulf may be landed near Arnold's point, upon the eastern bank, and a road being made from the post . . . they might be transported by wagons across in three days. It would be preferable, however, to establish a depot . . . from which a small steamboat could carry more to the post in twenty-four hours than a hundred wagons could transport in a week. Either of these methods would be far preferable to the present slow, laborious and uncertain mode of supplying by wagons and pack mules . . . from San Diego.8
The effect of the Derby report was far-reaching, first, because it expressed a conviction that the river was navigable, and secondly, because it led directly to the first step in the introduction of steam navigation on the Colorado River, the testing period. It was upon the outcome of these tests during the next decade that the success or failure of the experiment was to be determined. Meanwhile the stock of supplies at the post was reaching the point of depletion. Government action was characteristically slow, and on June 5, 1 85 1, with no relief in sight, it was necessary to abandon the Yuma post. Major Heintzelman returned to San Diego with the majority of his forces, leaving only a guard of one officer and ten men at the fort to afford protection to the ferry company.9 After the withdrawal of the troops, Indian hostilities increased, and on December 6 the remaining guard under Lieuten
