The Missouri River was an important artery of commerce for Native American villages of the Plains culture long before Europeans arrived. The French explorers Jacques Marquette and Louis Jolliet passed the mouth of the river in 1683 and the Canadian explorer Vérendrye visited the upper reaches of the river in 1738. David Thompson, a Canadian fur trader, explored part of the river in 1797. Meriwether Lewis and William Clark followed the Missouri on their journey (1803–6) to the Pacific Ocean and described it at length (see Lewis and Clark expedition). The first steamboat ascended the river in 1819, and hundreds more later navigated the uncertain waters to Fort Benton. Mormons bound for Utah and pioneers bound for Oregon and California followed the Missouri valley and that of the Platte overland to the West. River traffic declined with the loss of freight to the railroads after the Civil War. Although it was revitalized in the mid-20th cent., in the section below Sioux City, through the navigational improvements and flood control efforts of the Missouri River basin project, barge traffic declined in the late 20th cent. Two stretches of the river are protected as the Missouri National Recreational River (see National Parks and Monuments (table)).