Fortification Rock, once a landmark hill on the

Colorado River The Colorado River () is one of the principal rivers (along with the Rio Grande) in the Southwestern United States and in northern Mexico. The river, the List of longest rivers of the United States (by main stem), 5th longest in the United St ...

before it was inundated, now known as Rock Island, southernmost and tallest of the Boulder Islands in

Lake Mead Lake Mead is a reservoir formed by the Hoover Dam on the Colorado River in the Southwestern United States. It is located in the states of Nevada and Arizona, east of Las Vegas. It is the largest reservoir in the US in terms of water capacity. L ...

Clark County, Nevada Clark County is the most populous County (United States), county in the U.S. state of Nevada with 2,265,461 residents as of the 2020 United States census, 2020 census. The county is the location of the state's three largest cities, Las Vegas (t ...

. It has an elevation of 1284 feet. Fortification Rock appears on the 1861 Geological Map No. 1; Rio Colorado of the West, explored by 1st Lieut. Joseph C. Ives, which shows Fortification Rock, Ives Camp #59 and the course of the Colorado River from its mouth on the

Gulf of California The Gulf of California (), also known as the Sea of Cortés (''Mar de Cortés'') or Sea of Cortez, or less commonly as the Vermilion Sea (''Mar Vermejo''), is a marginal sea of the Pacific Ocean that separates the Baja California peninsula from ...

to Las Vegas Wash and the location of its features and other expedition camps along the way. Geological Map No. 1. Prepared by J.S. Newberry, M.D. Geologist to the Expedition. Explorations and Surveys. War Department. Map No. 1. Rio Colorado of the West, explored by 1st Lieut. Joseph C. Ives, Topl. Engrs. under the direction of the Office of Explorations and Surveys. A.A. Humphreys, Capt. Topl. Engrs. in Charge, by order of the Hon. John B. Floyd, Secretary of War. 1858. Drawn by Frhr. F.W.v. Egloffstein. Topographer to the Expedition. Topography by Frhr. F.W.v. Egloffstein. Ruling by Samuel Sartain. Lettering by F. Courtenay.
from davidrumsey.com, accessed June 12, 2015.

History

Fortification Rock, now an island, was before the building of Boulder Dam and the filling of Lake Mead, the tallest peak of a small range of hills, a landmark on the west bank of the

just above the top entrance to the Black Canyon of the Colorado. It was named by 1st Lieutenant Joseph Christmas Ives, March 11, 1858, during his 1857-1858 expedition to find the upper limit of navigation for the Colorado. It marked what he considered that highest point for

steamboat A steamboat is a boat that is marine propulsion, propelled primarily by marine steam engine, steam power, typically driving propellers or Paddle steamer, paddlewheels. The term ''steamboat'' is used to refer to small steam-powered vessels worki ...

navigation, during the June to October season of high water. He had left his steamboat ''Explorer'' behind at the mouth of the Black Canyon of the Colorado after it had struck Explorer's Rock at its mouth. While it was being repaired, he and the steamboat's captain and mate had ascended the canyon in a

skiff A skiff is any of a variety of essentially unrelated styles of small boats, usually propelled by sails or oars. Traditionally, these are coastal craft or river craft used for work, leisure, as a utility craft, and for fishing, and have a one-pers ...

portaging Portage or portaging ( CA: ; ) is the practice of carrying water craft or cargo over land, either around an obstacle in a river, or between two bodies of water. A path where items are regularly carried between bodies of water is also called a '' ...

over the rapids to camp two days later on the west riverbank at the foot of Fortification Rock, which had to him the appearance of a

fortification A fortification (also called a fort, fortress, fastness, or stronghold) is a military construction designed for the defense of territories in warfare, and is used to establish rule in a region during peacetime. The term is derived from Lati ...

. Ives climbed it to get a look at the land and course of the river upstream. Joseph C. Ives, REPORT UPON THE COLORADO RIVER OF THE WEST, EXPLORED IN 1857 AND 1858 BY LIEUTENANT JOSEPH C. IVES, CORPS OF TOPOGRAPHICAL ENGINEERS, UNDER THE DIRECTION OP THE OFFICE OF EXPLORATIONS AND SURVEYS, A. A. HUMPHREYS, CAPTAIN TOPOGRAPHICAL ENGINEERS, IN CHARGE. BY ORDER OF THE SECRETARY OF WAR, GOVERNMENT PRINTING OFFICE, WASHINGTON, 1861; PART I. GENERAL REPORT.
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References

{{authority control Landforms of Clark County, Nevada Lake islands of Nevada Colorado River