On November 14, 1803, at the confluence of the Ohio and Mississippi Rivers, the Corps of Discovery stayed for six days, one of the expedition's longest stops. There they saw the Mississippi for the first time, noted mistletoe on the large timber, and caught a 128 pound blue catfish. During the stay, Captain Lewis taught Captain Clark to use navigational equipment, including a compass and sextant, and because the 3rd Principal Meridian begins at the mouth of the Ohio, astronomical observations there were crucial. In 1803, President Thomas Jefferson commissioned U.S. Army officers Meriwether Lewis and William Clark to conduct an expedition to the Pacific coast through a region entirely unknown to European civilization, crossing the North American continent from the Mississippi River to the Pacific Ocean by way of the Missouri and Columbia Rivers. They left Pittsburgh on the Ohio River on August 31, 1803, on the eastern leg of the journey. The area south of Cairo in Alexander County, where the Mississippi and Ohio Rivers met, was forested with massive cottonwood and sycamore trees and thick with small cane and vines. In this area, they recorded over 178 plants and 122 animal species, including prairie chickens, Carolina parakeets, doves, swans, Canada geese, woodpeckers, and many species of ducks. Their expedition and discoveries opened the door for westward expansion and the growth of a new nation, a legacy for the last 200 years.