Great Falls  -  Ryan Dam Park, MT.  When Lewis located the falls, he sent a man back to the main party with instructions to go upstream and set up camp.  As Lewis searched for a portage route, he came upon four other falls, with dangerous rapids and cataracts between.  The party spent nearly a month portaging their heavy equipment and supplies 18 miles around the falls.  This was a major delay.
Photo:  ©Charley Van Pelt