only sailed from the river's mouth to Lewiston, located at the confluence of the Snake and Clearwater rivers. This stretch of the river is the easiest to navigate for watercraft since it has the least elevation change, although it still contained over 60 sets of rapids. Passenger and freight service downstream of Lewiston lasted throughout the late 19th century and persisted until the introduction of railroads in the Palouse Hills grain-growing region and ultimately, the construction of dams on the lower Snake to facilitate barge traffic, which caused the demise of both the steamboats and the railroad. Lewiston, from the confluence of the Snake and Columbia and from the mouth of the Columbia on the Pacific Ocean, became connected with Portland and other Pacific ports via steamboat service from the mouth of the Snake through the Columbia River Gorge. A commonly traveled route was from Wallula, Washington, downstream of the Snake River's mouth, upstream to Lewiston. The Oregon Steam Navigation Company launched the Shoshone at Fort Boise in 1866 which provided passenger and freight service on the upper Snake for the Boise and Owyhee mines. By the 1870s, the OSN Company, owned by the Northern Pacific Railroad, was operating seven steamboats for transporting wheat and grain from the productive Palouse region along the Snake and Columbia to lower Columbia River ports. These boats were the Harvest Queen, John Gates, Spokane, Annie Faxon, Mountain Queen, R.R. Thompson, and Wide West, all of which were built on the Columbia River. However, there were more resources along the Snake River than wheat and grain. In the 1890s, a huge copper deposit was discovered at Eureka Bar in Hells Canyon. Several ships were built specifically to transport ore from there to Lewiston: these included Imnaha, Mountain Gem, and Norma. In 1893 the Annie Faxon suffered a boiler explosion and sank on the Snake below Lewiston. River modifications Dams A total of twenty dams have been constructed along the Snake River for a multitude of different purposes, from its headwaters in the Rocky Mountains to its mouth on Lake Wallula, the reservoir formed behind McNary Dam on the Columbia River. Dams on the Snake can be grouped into three major categories. From its headwaters to the beginning of Hells Canyon, many small dams block the Snake to provide irrigation water. Between the headwaters and Hells Canyon, the first dam on the Snake, Swan Falls Dam,