Q: In this task, you're given passages that contain mentions of names of people, places, or things. Some of these mentions refer to the same person, place, or thing. Your job is to write questions that evaluate one's understanding of such references. Good questions are expected to link pronouns (she, her, him, his, their, etc.) or other mentions to people, places, or things to which they may refer. Do not ask questions that can be answered correctly without understanding the paragraph or having multiple answers. Avoid questions that do not link phrases referring to the same entity. For each of your questions, the answer should be one or more phrases in the paragraph, and it should be unambiguous.
Passage: Lorenzo Sitgreaves led the first Corps of Topographical Engineers mission across northern Arizona to the Colorado River (near modern Bullhead City, Arizona), and down its east bank to the river crossings of the Southern Immigrant Trail at Fort Yuma in 1851.The second Corps of Topographical Engineers expedition passed along and crossed the Colorado was the 1853-1854 Pacific Railroad Survey expedition along the 35th parallel north from Oklahoma to Los Angeles, led by Lt. Amiel Weeks Whipple.George A. Johnson was instrumental in getting the support for Congressional funding a military expedition up the river. With those funds Johnson expected to provide the transportation for the expedition but was angry and disappointed when the commander of the expedition Lt. Joseph Christmas Ives rejected his offer of one of his steamboats.  Before Ives could finish reassembling his steamer in the delta, George A. Johnson set off from Fort Yuma on December 31, 1857, conducting his own exploration of the river above the fort in his steamboat General Jesup.  He ascended the river in twenty one days as far as the first rapids in Pyramid Canyon, over 300 miles (480 km) above Fort Yuma and 8 miles (13 km) above the modern site of Davis Dam.  Running low on food he turned back.   As he returned he encountered Lieutenant Ives, Whipple's assistant, who was leading an expedition to explore the feasibility of using the Colorado River as a navigation route in the Southwest.  Ives and his men used a specially built steamboat, the shallow-draft U.S.S. Explorer, and traveled up the river as far as Black Canyon.  He then took a small boat up beyond the canyon to Fortification Rock and Las Vegas Wash.  After experiencing numerous groundings and accidents and having been inhibited by low water in the river, Ives declared: "Ours has been the first, and will doubtless be the last, party of whites to visit this profitless locality. It seems intended by nature that the Colorado River, along the greater portion of its lonely and majestic way, shall be forever unvisited and undisturbed."Until 1866, El Dorado Canyon was the actual head of navigation on the Colorado River. In that year Captain Robert T. Rogers, commanding the steamer Esmeralda with a barge and ninety tons of freight, reached Callville, Nevada, on October 8, 1866.  Callville remained the head of navigation on the river until July 7, 1879, when Captain J. A. Mellon in the Gila left El Dorado Canyon landing, steamed up through the rapids in Black Canyon, making record time to Callville and tied up overnight.  Next morning he to steamed up through the rapids in Boulder Canyon to reach the mouth of the Virgin River at Rioville July 8, 1879.  From 1879 to 1887, Rioville, Nevada was the high water Head of Navigation for the steamboats and the mining company sloop Sou'Wester that carried the salt needed for the reduction of silver ore from there to the mills at El Dorado Canyon.
A:
What is the last name of the person who ascended the river in twenty one days as far as the first rapids in Pyramid Canyon?